Optimising Urban Micro AD Networks

Feasibility study

Optimising Urban Micro AD

Networks

Using micro anaerobic digestion to create small-scale community-based food waste recycling capability and renewable energy within urban environments

Project code: OIN001-010 Research date: March – July 2012 Date: November 2013

WRAP‟s vision is a world without waste, where resources are used sustainably. We work with businesses, individuals and communities to help them reap the benefits of reducing waste, developing sustainable products and using resources in an efficient way. Find out more at www.wrap.org.uk This report was commissioned and financed as part of WRAP‟s „Driving Innovation in AD‟ programme. The report remains entirely the responsibility of the author and WRAP accepts no liability for the contents of the report howsoever used. Publication of the report does not imply that WRAP endorses the views, data, opinions or other content contained herein and parties should not seek to rely on it without satisfying themselves of its accuracy. Document reference: [e.g. WRAP, 2006, Report Name (WRAP Project TYR009-19. Report prepared by…..Banbury, WRAP]

Written by: Rokiah Yaman, Angie Bywater, James Murcott, Guy Blanch, David Neylan, Davide Poggio, Mark Walker, Clive Andrews, Cath Kibbler

Front cover photography: Courtesy of Fernanda Costa and Camden TSB Project

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Optimising Urban Micro AD Networks 1

Executive summary

This report explored the feasibility of establishing a micro anaerobic digestion (AD) network in an urban environment. The network is designed to demonstrate a range of biogas applications including space heating and biogas upgrading for fuel cell CHP and vehicle use. The range of participating host sites spans educational, business and community sectors, further demonstrating the versatility of the technology. Research investigating technical and economic feasibility involved:

identifying and assessing potential sites;

looking at the separate subsystems;

deciding how they might be scaled or optimised;

identifying suitable, robust equipment;

assessing integration considerations between each sub-system;

identifying and assessing the monitoring and control system objectives;

ascertaining costs and quantifying operational parameters and parasitic loads; and

creating the mass energy balance and economic assessment models.

Several themes were highlighted across the technical evaluation results including the importance of:

delivering low-cost designs at small scale;

scaling technology for limited urban footprints; and

minimising parasitic loads to ensure net energy and economic gains.

The report established that many of the elements present in a larger AD system can be scaled down for use in micro AD systems, but that the overall economics of using a particular piece of equipment depend upon a number of factors, including site-specific elements, such as quantity of waste available, ability to use the digestate and existing waste disposal costs. To this end, four micro AD system configurations have been proposed for Phase 2, each of varying size and sophistication in terms of pre-digestion, gas use and digestate handling. Each host site will be equipped with full remote monitoring and control capacity to provide valuable data for a thorough evaluation for the project. The cost benefit analysis concluded the following system costs and payback periods for each site:

site 1 - £5,984 – 3.2 years;

site 2 - £18,395 – 6.4 years;

site 3 - £37,664 – 11.5 years; and

site 4 - £91,416 – 5.3 years. The concept of a micro anaerobic digestion network offers a level of coordination between sites as well as shared learning and best practice, thus enabling expertise to develop faster. The network can also buffer individual system downtime as other sites may temporarily accommodate extra feedstock. The range of participating host sites spans educational, business and community sectors, further demonstrating the versatility of the technology.


Contents

1.0 Introduction and background ....................................................................... 8 1.1 Issues addressed in the AD industry ............................................................ 8 1.2 Study objectives ......................................................................................... 8

1.2.1 Economic expectations ..................................................................... 9 1.2.2 Technical expectations ..................................................................... 9

1.3 Aims of the demonstration .......................................................................... 9 1.4 Introduction to the technology .................................................................. 10

1.4.1 What are the origins of technology? ................................................ 10 1.4.2 What has been achieved to date? .................................................... 11

1.5 How the technology and demonstration meet the WRAP DIAD II objectives .. 11 1.5.1 General benefits ............................................................................ 11 1.5.2 Waste reduction ............................................................................. 12 1.5.3 Technology development and optimisation ....................................... 12 1.5.4 Developing a market for digestate ................................................... 12 1.5.5 Disseminating information and building AD expertise ........................ 12 1.5.6 Heat use ....................................................................................... 13 1.5.7 Full-scale demonstration capacity .................................................... 13 1.5.8 Industry links ................................................................................. 13 1.5.9 Market pull .................................................................................... 13

1.6 Company/consortium ............................................................................... 13 2.0 Technology descriptions, selection and evaluations ................................... 15

2.1 Pre digestion ........................................................................................... 15 2.1.1 Technology description ................................................................... 15 2.1.2 Pre digestion technology selection - Sites 2 and 4 ............................. 16 2.1.3 Pre digestion evaluation results ....................................................... 17

2.2 Digestion ................................................................................................. 18 2.2.1 Digester technology description ....................................................... 18 2.2.2 Digester technology selection .......................................................... 18 2.2.2.1 1m3 IBC digester - Site 1 ............................................................. 18 2.2.2.2 2m3 and 6m3 Biogastronomes - Sites 2 and 3 ................................ 19 2.2.3 Digester evaluation results .............................................................. 20 2.2.3.1 1m3 IBC digester - Site 1 ............................................................ 20 2.2.3.2 2m3, 6m3 and 20m3 digesters - Sites 2 and 3 ................................ 21

2.3 Gas handling ........................................................................................... 22 2.3.1 Gas scrubbing technology description .............................................. 22 2.3.2 Gas scrubbing technology selection - Sites 2 and 3 ........................... 22 2.3.3 Gas Scrubbing technology evaluation results - Sites 2 and 3 .............. 24 2.3.4 Gas scrubbing technology selection - Site 4 ...................................... 25 2.3.5 Gas handling evaluation results - Sites 3 and 4 ................................. 28

2.4 Digestate handling ................................................................................... 29 2.4.1 Digestate handling description ........................................................ 29 2.4.2 Digestate handling technology selection ........................................... 29 2.4.3 Digestate processing technology evaluation results ........................... 30

2.5 Monitoring and control system .................................................................. 32 2.5.1 Monitoring and control system description ........................................ 32 2.5.2 Monitoring and control system technology selection .......................... 32 2.5.3 Monitoring and control system evaluation results .............................. 33

3.0 Site selection and evaluation ...................................................................... 36 3.1 Site selection ........................................................................................... 36 3.2 Site evaluation results .............................................................................. 39

4.0 Network evaluation and cost benefit analysis ............................................ 42


4.1 Inputs and outputs including energy balance and mass balance, process flow and/or other technical diagrams .......................................................................... 42 4.2 Comparison with „business as usual‟ and other technologies ........................ 44 4.3 Cost to industry/facilities including capex and opex ..................................... 46 4.4 Cost Benefit Analysis ................................................................................ 46 4.5 Environmental cost benefit analysis ........................................................... 48

5.0 Legislation .................................................................................................. 50 5.1 Regulations and legislation applicable to the wider development and/or installation of micro AD in the UK ........................................................................ 50

5.1.1 Environmental permitting ................................................................ 50 5.1.2 Exemptions ................................................................................... 50

5.2 Registering exemptions ............................................................................ 51 5.2.1 Animal By-Products Regulations ...................................................... 52 5.2.2 ABPR exemption for small-scale community composting/digestion ...... 52

6.0 Commercialisation of technology ............................................................... 54 6.1 The IP landscape ..................................................................................... 54

6.1.1 The open source route ................................................................... 54 6.1.2 Control system protection ............................................................... 55

6.2 Overview of commercialisation plans.......................................................... 55 6.3 Market research ....................................................................................... 55

6.3.1 Export potential for micro AD .......................................................... 58 6.3.2 Competitors ................................................................................... 58

6.4 Sales projections ...................................................................................... 58 6.5 Manufacturing plans ................................................................................. 59

7.0 Conclusion .................................................................................................. 60 Phase 2: Demonstrations ..................................................................................... 61 8.0 Objectives of the demonstrations ............................................................... 61 9.0 Methodology for demonstration ................................................................. 62

9.1 Delivery of the demonstration ................................................................... 62 9.2 Key project milestones for Phase 2 ............................................................ 63 9.3 Project timescale ...................................................................................... 64 9.4 Permitting & other approvals ..................................................................... 65 9.5 Feedstock sources .................................................................................... 65

10.0 Cost breakdown .......................................................................................... 66 10.1 Project finance ......................................................................................... 68

11.0 Evaluation and monitoring ......................................................................... 69 11.1 Monitor during the demonstration phase .................................................... 69

12.0 Key personnel, subcontractors and their roles ........................................... 70 13.0 Health, safety and risk ................................................................................ 72

13.1 Key H&S considerations ............................................................................ 73 Appendix 1 – Site information .............................................................................. 74 Appendix 2 – Market research tables ................................................................... 78 Appendix 3 – Control and monitoring .................................................................. 83

3.1 Control and monitoring system evaluation .................................................. 83 3.2 Selection and description of the sensors ..................................................... 83

3.2.1 Gas flow ........................................................................................ 84 3.2.2 Gas composition ...................................................................................... 84

3.2.3 pH ................................................................................................ 85 3.2.4 Current transducers ....................................................................... 85

3.3 Selection and description of the electronic hardware components................. 85 3.4 Validation of sensor data .......................................................................... 85

3.4.1 Missing data .................................................................................. 86 3.4.2 Values out of range .................................................................................. 86 3.4.3 Rate of change check ............................................................................... 86


3.4.4 Constant measurement value .................................................................... 86 3.5 The Monitoring System and Interface with the User and Cloud ..................... 86 3.6 Control system design and simulation ........................................................ 91 3.7 Simulation of the control system performance vs. „Business as usual‟ ........... 91

Appendix 4 – Gas application and scrubbing evaluations .................................... 97 4.1 CHP Units ................................................................................................ 97

4.1.1 Long-term feasibility of fuel cell CHP units ........................................ 98 4.2 Investigating gas requirements for compression and combustion ................. 99

4.2.1 Dew point limit .............................................................................. 99 4.2.2 Compression limits ......................................................................... 99 4.2.3 Combustion stability ..................................................................... 100

4.3 Gas scrubbing literature review summary by UCL collaborative programme . 101 Appendix 5 – Economic assessment ................................................................... 103 Appendix 6 – HACCP ........................................................................................... 105

Figures

Figure 1 - Breaker mill results 16 Figure 2 - 0.2m3 Biogastronomy digester 19 Figure 3 - Typical simple gas storage vessels 24 Figure 4 - Solubility of CO2 in water at atmospheric pressure versus temperature 25 Figure 5 - Larger-scale gas scrubbing system for scaling 26 Figure 6 - Scrubbing tower biomethane upgrading system 28 Figure 7 - AD Schematic - Green dotted line shows digestate post-treatment system 29 Figure 8 - Design of control system 35 Figure 9 - Proposed network sites for the Phase 2 demonstration 37 Figure 10 - Amalgamated process flow 44 Figure 11 - Project timescale 64 Figure 12 - Example algorithms for derived quantities in monitoring system 87 Figure 13 - Selected sensors for the control and monitoring system 88 Figure 14 - Modelling scenario used to test the control system 92 Figure 15 - Demand profiles 92 Figure 16 - Excess biogas production and unmet demand in all eight simulated scenarios 94 Figure 17 - AD system behaviour example 95 Figure 18 - Dew point calculations 99 Figure 19 - DEW calculations at varying temperatures 100 Figure 20 - Net calorific value (NCV) at varying CO2 percentages 100 Figure 21 - Flame Stability over Weaver speed factors 101 Figure 22 - Diagram of membrane separation process (Source: Faure et al., 2012) 102

Tables

Table 1 - Results of digestion trials at the University of Southampton carried out from November 2007 to March 2008 ...................................................................................... 20 Table 2 - Biogas composition before and after scrubbing ................................................ 24 Table 3 - Basic mass balance for the proposed sites ....................................................... 42 Table 4 - Energy balance of proposed systems .............................................................. 43 Table 5 - Local micro networks vs large centralised plants .............................................. 45 Table 6 - Performance of the controlled and uncontrolled systems .................................. 46 Table 7 - System budget prices .................................................................................... 46 Table 8 - Summary site economics ............................................................................... 48


Table 9 - Tonnes of CO2 equivalent emissions avoided ................................................... 49 Table 10 - CO2e emissions (kg/yr) through biomethane use ............................................ 49 Table 11 - Risk matrix and questionnaire ...................................................................... 52 Table 13 - Key project milestones for Phase 2 ............................................................... 63 Table 14 - Cost breakdown .......................................................................................... 66 Table 15 - Phase 2 risk assessment .............................................................................. 72 Table 16 - Site assessment details ................................................................................ 75 Table 17 - TSB Future Cities market research ................................................................ 78 Table 18 - Imperial College report ................................................................................ 80 Table 19 - LEAP 2012 food waste survey results ............................................................ 81 Table 20 - Summary of simulation results ..................................................................... 93 Table 21 - The Gamma Premio (BGP) ........................................................................... 97 Table 22 - Specific requirements at the supply point on the H network ............................ 98 Table 23 - Specific requirements at the supply point on the L network ............................ 98


Glossary

ABS – Acrylonitrile butadiene styrene, a common type of plastic.

AD – Anaerobic digestion: Biological degradation in an oxygen-free environment.

AHVLA – Animal Health Veterinary Laboratories Agency work on behalf of Defra to safeguard animal and public health.

ATEX – is a contraction of the French title of two European directives describing what equipment and work environment can be used in areas with a potentially explosive atmosphere.

BRC5 – British Retail Consortium 5, a global standard which lays down stringent criteria regarding a number of critical food safety issues.

CAPEX – Capital expenditure.

CHP – Combined Heat and Power plant. An engine which generates both heat and electricity.

CIWM – Chartered Institute of Waste Management, a professional body representing waste and resource professionals, responsible for setting professional standards.

CO2e – Carbon dioxide equivalent, a measure used in assessing greenhouse gas emissions.

DEFRA – Department for Environment, Food and Rural Affairs – the UK Government department responsible for policy and regulation on the environment, food, farming and rural affairs. Defra is responsible for part-funding the Environment Agency (see below).

Digestate – Digestate is a by-product of the anaerobic digestion process. It can be used whole, or separated into liquid and solid fractions and used on land as a fertiliser and soil conditioner.

DM – Dry matter - the dry content of an AD feedstock.

EA – Environment Agency, the UK Public Body responsible for, amongst other things, permitting for anaerobic digestion plants.

FITs – Feed in Tariffs, incentives for creating renewable energy.

GRP – glass-reinforced plastic (fibreglass).

I/O – Input/output, where input signals/data are received by a system and it also sends signals/data.

kW – kilowatt, a measure of power.

kWh – kilowatt hour, the amount of power consumed/generated over a period of one hour.

kWth – kilowatt thermal – refers to heat (thermal) power produced, eg by a CHP.

kWe – kilowatt electric – refers to electrical power produced, eg by a CHP.

LBC – London Borough of Camden.

mb – millibar, a measure of atmospheric pressure.


NOx – oxides of Nitrogen, NO and NO2, produced from nitrogen reacting with oxygen, usually during combustion.

NVZ – Nitrate Vulnerable Zone. These are EA designated areas of land subject to a number of special rules, including slurry storage and spreading times and quantities.

O&M – Operations and maintenance.

oDM – Organic dry matter – the potentially digestible portion of the dry matter of a given feedstock.

PPM – parts per million, used to quantify small masses, eg H2S in biogas.

RHI – Renewable Heat Incentives, UK government incentives to create renewable heat. SME – Small/Medium Enterprises which, in a European context, meet a certain number of conditions, one of which is that they employ fewer than 250 people. TS – The total solids in a given feedstock, made up from volatile solids and inerts. VFA – Volatile Fatty Acids, a measure of which can indicate the stability of the AD process; high levels of VFAs on food waste only digesters caused by trace element deficiency can cause a failure in the digestion process. VS – Volatile solids, a measure of what portion of the organic matter can be transformed during anaerobic digestion; technically, those solids which are lost on ignition of the dry solids of a substrate at 550oC.


1.0 Introduction and background

1.1 Issues addressed in the AD industry The importance of reducing organic waste to landfill and subsequent methane emissions is currently reflected in rising landfill tax in England, the Welsh commitment to zero waste by 2050 and the impending Scottish ban on organics to landfill. In light of this, AD has become one of the technologies of choice in managing organic resources, avoiding greenhouse gas emissions and generating base load renewable energy in the UK. While large farm-scale AD is of great environmental and economic benefit to the UK, it is not the whole solution. Urban areas such as London are, or will soon be, required to manage waste within their boundaries, with the GLA aiming for 85% self-sufficiency in waste treatment methods that enable citizens to receive environmental and economic benefits. However, despite proximity to concentrated sources of feedstocks and significant energy demands, the construction of large AD systems in urban areas is extremely problematic due to high costs, public objection, lack of land space for digesters and digestate, and the extra traffic involved in transporting feedstocks and digestate. Although some progress had been made developing smaller-scale AD technology, urban areas are still less able to benefit from a technology that could, if deployed in small decentralised networks, reduce waste miles and support local energy security due to space restrictions and high capital costs. This project aims to address these barriers by demonstrating a network of cost-effective urban micro AD systems running largely on local food and non-woody garden waste. The network would provide low-cost, low-impact waste treatment systems, a closed-loop cycle that could support communities with renewable energy and fertiliser for local food growing and urban greening projects. To fully engage with the concept and value of closed-loop sustainable organic resource management, people need to see it in action. Community-led projects with local benefits tend to have greater community participation and buy-in. The existence of such digesters would offer a huge and accessible potential educational resource, directly capable of leading to behavioural change and increasing public engagement in waste reduction and recycling. The project hopes to make a contribution to the sector by raising the visibility of AD, boosting public awareness and support for the technology and delivering multiple community benefits through the establishment of closed-loop systems.

1.2 Study objectives This study aims to pave the way for delivery of a full-scale demonstration of a range of micro AD systems and biogas applications that incorporate technology developments and modifications designed to:

feedstock conditioning/pre-digestion;

improve cost-effectiveness;

optimise operational and process efficiency;

reduce equipment footprint; and

enhance user friendliness.

In determining the economic viability of micro AD, the costs of several sizes and types of micro digester systems with mixed configurations (e.g. with and without pre-treatment) were analysed, taking into account the carbon savings of digesting the various substrates, as well as comparing the cost of AD with the current disposal costs of organics.


An assessment of the feasibility of optimising market ready technology, transferring knowledge from other sectors, and scaling larger equipment commonly used in AD or other industries was made in order to inform the design of the following sub-systems:

feedstock conditioning/pre-digestion;

digester heating and mixing;

gas collection, cleaning and use;

digestate processing; and

monitoring and control integration.

1.2.1 Economic expectations It was expected that capital and operational costs vs. the energy production for micro AD would be critical to their success as commercial entities. Therefore, the technology used for each component would have to be as simple and energy-efficient as possible. AD economics depends upon waste management savings made, income from energy production, and a modest income from digestate sales/use. Micro systems may easily access local organic waste, supplement local energy and supply local fertiliser needs, however, their scale limits profitability in these areas, while other savings and benefits remain economically invisible, despite meeting many of the legal, environmental and social objectives of urban areas. 1.2.2 Technical expectations It was expected that some components may be more scalable than others and that some low-cost options may lack operational effectiveness or have high parasitic energy requirements. Conversely, more efficient solutions may present higher costs. A „worst case‟ scenario would be that, for a particular part of the digester system, a suitably efficient and cost effective solution could not be found. From a control point of view, it was expected that the basic plant operation could be achieved using relatively cheap equipment such as micro-switches, timers, thermostats, water heaters for temperature control, and geared motors for stirring. The second level control (expert controller) would be implemented using more sophisticated and expensive sensors for gas, biogas production and pH with an algorithm based on the inputs to set the feeding rate.

1.3 Aims of the demonstration The demonstration will seek to establish the value of low-risk, robust, flexible systems across a range of settings including an ecology educational centre, a community centre/garden and a food manufacturing SME. In doing so, the project will gather valuable operational data and promote increased market penetration of micro AD. The choice of a number of digester configurations, biogas applications and the systems‟ relatively low capital cost and simplicity, will demonstrate the versatility of the technology and allow users to start with an AD plant appropriate to available feedstocks and site requirements. Showcasing the network in Kings Cross, an area undergoing a major transformation in the heart of London, ensures a high-profile accessible location from which to publicise the benefits of the technology. While the project is situated within an urban setting, the technology design will be suitable for both urban and rural environments.


To effectively manage digestate distribution, the project will utilise partners‟ existing contacts to target golf courses, city parks, allotments, community gardens and food growing networks (including Capital Growth) and green infrastructure maintenance teams including green roofs/walls and office planting. In addition, local authority distribution channels will also be employed including the NLWA (North London Waste Authority) Eco Compost Hubs. 1.4 Introduction to the technology

The term micro AD has different meanings in different contexts, with perceptions of scale being skewed upwards with the advent of the feed-in tariff. Before its introduction, „full‟ farm-scale digesters could be defined as 30m3 and upwards. Meanwhile, the ubiquitous „standard‟ Chinese digester is in the region of 6m3 and, although an appropriate farm-scale size, would likely be considered „micro‟ by many. For the purposes of this paper, the term „micro‟ will be used for digesters of 20m3 and below. This is an arbitrary figure however, as even a 20m3 digester could take a daily feed of several thousand kilograms of certain feedstocks, thus feedstock and digestate volumes require careful consideration. Such a digester could take food waste from around 400 families per day, based on WRAP‟s figures of 6-7 kg per family per week. The proposed network includes digester capacities of 1, 2, 6 and 20m3. In determining the technical feasibility of micro AD, opportunities to scale existing technology and transfer knowledge from other sectors were explored in order to find cost-effective, cold-climate solutions for:

Maceration: reducing feedstock particle size.

Pre-digestion: storage of macerated feedstock in an insulated tank to initiate hydrolysis.

Digestion: retention of feedstock in an insulated, gas tight tank where biogas is captured, and feedstock input is balanced by digestate output.

Biogas scrubbing and pressurising: removal of hydrogen sulphide, H2O and CO2 from biogas and pressurising to match gas appliance rates.

Digestate separation: simple separation of digestate into liquid and fibre constituents prior to storage and distribution.

The project also focused on establishing remote monitoring and control capability across the proposed network, designed to function over three tiers:

Tier 1: maintaining safe and effective basic operation and fault detection.

Tier 2: functioning as an „expert controller‟, assessing the current state of biological process, maintaining stable operation and meeting control objectives.

Tier 3: functioning as a „remote supervisor‟ with two-way internet communication.

The novelty of the proposed technology lies in the latter two tiers: the expert controller and the remote supervisor, as most sensors and machinery come with embedded fault detection mechanism, which signal abnormal conditions.

1.4.1 What are the origins of technology?

Today, over 25 million micro-scale biogas systems are operational worldwide. These digesters range from simple drum digesters found in warm-climate peasant farms, to the bag design used in Taiwan and Central America. In these small AD plants, equipment design is relatively „low tech‟ and no process control has been necessary, as fixed rules based on constant loading rates are sufficient. This is


acceptable, since these systems have a naturally high biological and operational robustness due to simple designs (single stage, no heating or mixing, gravity feeding), use of exclusively liquid feedstocks (animal slurries) with low biogas productivity. In contrast, during the last 15 years in the West, AD as a renewable waste-to-energy technology has centred on large, high-tech farm installations, with plants in the order of 1000m3

- 3000m3 capacity, and power units in the MW range. High capital costs and significant attendant risks have ensured that only a small segment of the agricultural sector is in a position to take advantage of this technology.

1.4.2 What has been achieved to date? As an emerging technology, micro AD in the West draws on work that spans academic, manufacturing and community sectors, with the potential for the UK to take a lead in the market. Methanogen‟s 200L, 600L and 2m3 Biogastronomy digesters have been established at several sites, their design evolving over the last three years. The Bridport Renewable Energy Group is currently trialling a low-cost DIY-assembly community digester with the potential to greatly reduce capital costs for micro hosts. Other companies offering small-scale AD solutions include Aardvark (3.2kW Powerqube) and Burdens Energy (60kW system), however, these are currently either too big and/or too expensive for widespread urban applications. This project continues the work of the Community Composting Network who, since 2008, have facilitated micro AD test builds across a range of urban & rural sites, and commissioned three reports identifying micro AD components, operational protocols, case studies and areas for uptake. The project is also informed by LEAP‟s Technology Strategy Board Report, which examined logistics for a larger urban AD network, and by a recent University College London collaboration, which highlighted design issues and opportunities relevant to micro AD.

1.5 How the technology and demonstration meet the WRAP DIAD II objectives

1.5.1 General benefits

One of the great advantages of micro AD is that it brings the technology to people and communities where the benefits can be made tangible. For example, successful commercialisation leading to the widespread establishment of micro AD networks could contribute to local:

energy security;

employment and training opportunities;

food growing initiatives; and

educational and community engagement opportunities.

Wider benefits would also include:

diversion of organic waste from landfill;

reduced carbon footprint emissions from reduction of “waste miles” through local waste treatment;

carbon reduction through local organic fertiliser production replacing artificial, fossil fuel derived fertiliser; and

compliance with requirement to treat a certain proportion of waste within the borders of London.


Incorporating an integrated network-wide control system that can monitor, supervise and support successful operation will remove the need for expensive expert operators at each site and enable valuable data gathering and evaluation to inform further design refinements.

In addition, micro AD networks would confer the following benefits in alignment with WRAP DIAD II objectives.

1.5.2 Waste reduction

A small local AD network could offer buffering capacity working hand-in-hand with large out-of-town digesters in order to successfully handle reduced waste, where such reductions have been made through various initiatives including those carried out by WRAP i.e. it is more cost effective to re-site a £40K small digester if waste is reduced, than a £10m facility operating at 80% capacity and making a loss through reduced gate fees and tariff incentives.

In areas without large-scale AD plants, micro AD networks could act as a standalone solution for low-risk, low unit cost capacity/treatment expansion, with „larger‟ modular micro AD systems such as the containerised Powerqube or the Methanogen 20m3 added in response to increased organic collections, particularly those which may not be economic to transport large distances.

1.5.3 Technology development and optimisation

The proposed pre and post digestion components utilise scaled technology or knowledge transfer to optimise the micro AD process; increasing gas yield, reducing retention time, adding value to digestate and increasing the heating value of the gas produced. The market-ready Methanogen Biogastronomy digester will be optimised for the demonstration based on evaluation of the previous two years operation to improve overall cost-effectiveness and efficiency. The proposed online control and monitoring system will supply reliable operational data, which will be used for further technology development and optimisation as well as ensuring the project leaves a valuable legacy of learning.

1.5.4 Developing a market for digestate

Since digestate can be used locally within the London urban environment, the development of a low-risk, low-volume, sustainable local market for digestate alongside network expansion will ensure it does not become „a problem‟. Small-scale growing trials during the demonstration phase will explore the use of digestate for hydroponics, aquaponics, greenhouse and vertical growing in order to further enhance the value of digestate and demonstrate its use in a wide variety of applications particularly those suitable for urban applications.

1.5.5 Disseminating information and building AD expertise

Community by Design (CbD) and the Community Composting Network (CCN) have a proven track record of disseminating information on topics including community composting, community micro AD and air quality and are currently developing a CIWM accredited micro AD training programme. The Phase 2 demonstration will include delivery of this training to all


network sites. It will also be available for other interested groups, helping to impart O&M best practice as well as building AD expertise at the micro scale. Operational and design outputs will be disseminated through the CbD and CCN websites. In addition, CbD has working relationships with a number of local universities, most recently working with MSc students on a Collaborative Environmental Systems Programme at University College London focused on micro AD.

1.5.6 Heat use

At this scale, there are several feasible options, a number of which will be demonstrated across the network to avoid heat wastage. They include digester heating, cooking, and hot water and space heating via use of a modified gas boiler and a micro CHP unit. Space heating will be applied in at least one public space as well as within a small commercial greenhouse setting. Phase 1 will also explore the feasibility of utilising heat to support intensive urban agriculture and ground heating on one of the sites.

1.5.7 Full-scale demonstration capacity

A full-scale demonstration of the proposed network within the WRAP DIAD II timescale will build on CbD‟s pilot micro AD system, which received planning permission and financial support from the London Borough of Camden in 2012. Experience gained during the planning, infrastructure construction, assembly, commissioning and operation of this system will directly support the development of a WRAP Phase 2 demonstration.

1.5.8 Industry links

The project‟s established ties to industry partners Methanogen, Alvan Blanch engineer, Guy Blanch, Aleka Designs, Microgen, Ceramic Fuel Cells and Gas Fill will ensure access to industry expertise and contacts, competent technical delivery and delivery of a commercial scale demonstration.

1.5.9 Market pull

Through the partnership‟s recent Technology Strategy Board‟s technical feasibility study and cost benefit analysis supported by the London Borough of Camden, a market pull has been identified with over twelve sites approved and evaluated in less than three months including commercial properties, street markets, entertainment venues, transport depots, supermarkets, factories, community centres, social housing estates, a city farm and park.

The proposed WRAP Phase 2 demonstration will capitalise on the substantial local interest already generated, working with three of the sites identified to embed the technology in a sympathetic, engaged community.

1.6 Company/consortium Community by Design (CbD) is a not-for-profit social enterprise dedicated to delivering tangible community benefits through projects that combine social, environmental and economic outcomes. To date, its successful track record spans community arts, health and wellbeing, environmental education, community engagement, green construction and micro AD design and feasibility studies.


In 2011, CbD formed LEAP, a cross-sector partnership with the London Wildlife Trust and the Community Composting Network‟s (CCN‟s) Micro AD steering group, which includes links with Methanogen, independent engineers and AD academics. Funded by LBC, LEAP aims to develop micro AD in order to generate green employment, training and educational opportunities and empower local communities by harnessing the growing grassroots movement towards sustainable resource management. Its pilot micro AD system is situated near Kings Cross in the heart of London.

The partnership has made UK industry links with micro CHP companies Microgen and Ceramic Fuel Cells Ltd. Microgen have already trialled their Stirling engine (found in several domestic CHP units such as Baxi‟s Ecogen) with biogas, and are keen to see a high-profile demonstration. Ceramic Fuel Cell‟s Bluegen (domestic methane fuel cell CHP) are interested in trialling their unit with a blend of natural gas and biogas. Successful demonstrations could help unlock new markets for both micro CHP and micro AD. For this project, CbD will be working with:

The Community Composting Network - instrumental in the development of micro AD in the UK since 2008;

Methanogen UK Ltd - 35 years‟ experience in digester design and engineering from large to small scales;

Alvan Blanch research engineer - Guy Blanch - Alvan Blanch are experts in materials handling including pasteurisation, maceration and liquid/solid separation;

PhD researchers from Leeds University - currently working on a parallel, multi-University, control focused community-scale micro generation project – BURD (Bridging the Urban Rural Divide);

Dr David Neylan and the Bridport Renewable Energy Group who are developing a low-cost, DIY digester made from easily obtainable components; and

Aleka Designs – specialists in electronics design, prototyping and commercialisation.


2.0 Technology descriptions, selection and evaluations Micro AD technology is fundamentally a „system‟ based engineering process, i.e. a number of sub-systems working independently, but with a level of coherence between the sub-systems to help optimise the decentralised treatment and utilisation of bio-wastes. The whole system has to be simple and robust, comply with regulations and produce sanitised effluent or digestate suitable for horticulture. The following sections describe the various sub-systems of the technology, detail equipment selections and show evaluation results for each component in turn. To progress these evaluations further, the following will be assembled, tested and monitored at Camley Street Natural Park (Site 2) between June and September 2013, i.e. before the WRAP demonstration period:

mill and pre-digester tank;

2m3 digester;

digestate settling tank and storage;

gas scrubbing (H2S, moisture and CO2); and

monitoring and control system.

As the demonstration proposal involves multiple sites, each with different system configurations, the descriptions below cover all possibilities, while individual site-specific configurations are detailed in Appendix 1. Drawings for each component can be found in the separate drawings attachment. 2.1 Pre digestion 2.1.1 Technology description Maceration and pre-digestion is entirely optional, i.e. not necessary under the T25 exemption, which will apply to all the installations in the proposed network, but where budgets allow or operational considerations require its inclusion, it offers the advantages outlined below:

increasing the surface area for reaction;

reducing the viscosity of the liquidised feedstock, allowing consistent mixing/pumping in the subsequent process stages;

minimsing water consumption levels;

increasing biogas yield per quantity of feedstock and reducing retention time by accelerating the rate-limiting step of hydrolysis; and

improving the enterprises overall profitability.

The pre-digester vessel provides useful „buffer‟ storage capacity during the collection process. Waste will no longer need storing in an aerobic environment prior to being fed into the digester, increasing potential odour leaks from storage containers and requiring further handling. Loading times can be flexible with digester feeding regimes controlled by a simple timer and pump in conjunction with a weight indicator, thus saving the operator from having to be present at every feed time. The rate of feeding can be also regulated by an advanced diagnosis of the digester state described in 2.1.5. In urban environments where space is likely to be at a premium, pre-digestion may help reduce digester size by accelerating the fermentation process. Automated pre-digestion systems can also be used to feed a number of digesters automatically on the same site, useful for sites looking to increase their collection „catchment‟ area/feedstock input quantity.


While established off-the-shelf maceration equipment is readily available for large-scale digesters and standard kitchen sink waste disposal units have been successfully deployed as pre-treatment equipment for domestic-scale digesters, this study looks at scaling the technology to suit micro applications between 1-20m3. 2.1.2 Pre digestion technology selection - Sites 2 and 4 This project will utilise cost-effective milling equipment, transferred from the agricultural equipment sector scaled down by GBBD Ltd. The mill‟s „knifeless‟ feature helps reduce damage caused by heavy contamination, e.g. cutlery, stones, etc. During maceration, water (mains, grey or recovered rainwater) can be used sparingly to dilute any incoming high solid content feestock.

Figure 1 - Breaker mill results

The feedstock will be milled through an 11mm screen and blended to a suitable viscosity. Depending on the site, it is then transferred into the pre-digestion vessel either by gravity, manual loading by container, or transfer auger screw. The horizontal, cylindrical pre-digestion vessel features a mechanical stirrer with twin blades on a central driveshaft powered by a small gear motor or hand crank option to homogenise incoming feedstock. The bottom of the vessel is configured with a grit trap enabled by a valve, which is drained regularly to prevent excessive grit build up to reduce contamination of the digester.


The vessel is insulated to minimise heat loss and aid operational performance in winter and mounted on load cells, which instantly provide the operator with a level indication, removing the need to open the equipment. The indicator provides volume/weight feedback to the control system and can be used to regulate the feed rate into the digester. The unit will be modified with „wet protection‟ to protect bearings, seals and electrical points from dirt ingress, thus enabling a confident wash down after operation to help minimise odours and insect levels. For added corrosion protection, the unit will also be hot dipped zinc galvanised to combat the corrosive nature of food waste. Maintenance is minimal due to the selection of „sealed for life‟ bearings. Wearing parts in the mill are heavy-duty, hardened steel and will require changing every two years.

2.1.3 Pre digestion evaluation results Research revealed a number of issues with reducing the size of the mill; primarily the necessary reduction in size of the inlet feed hopper and the need to keep component cost within budget to maintain economic feasibility. Site 2 has a particularly small footprint and operating head space constraints in which to locate the milling and pre-digester equipment, requiring a re-design of the feed hopper from the vertical to a horizontal position with the mounting arrangement changing from a free standing to a top-mounted unit on the pre-digestion tank. To suit the feedstock feeding regime of 35kg/day at Sites 2 and 400kg/day at Site 4, the proposed maceration mill has been scaled down from a larger agricultural version sold by Alvan Blanch Development Co Ltd for use in the feed milling industry. This equipment is usually fitted with a three-phase motor to suit larger applications, but has been resized with a smaller 1.5 kW single-phase electrical unit for Site 2, to help reduce costs and still meet the performance requirements. Site 4 will use a 3kW 3-phase unit. To avoid using large powerful pumps to cope with very small pipework sizes, it was found during testing, that pipe size dimensions cannot be scaled down to the same degree, because of high pressure, frictional levels etc. The proposed automatic weight control/feeding system should reduce expensive labour charges associated with regular digester feeding, crucial for establishing micro AD in the Western hemisphere. For example, assuming a basic typical feeding operation takes 30 minutes every day of the year, the following savings could be realised: Time (hr) 0.5 * Labour @ £6.50 ph * 365 (days per annum) = £1186. The automated weighing system / top-up pre-digester levels will need loading Time (hr) 1 * Labour @ £6.50 ph * 96 (days per annum) = £624.

Challenges were found in keeping component costs & parasitic loads low enough to achieve economic feasibility. Traditional equipment, such as loading shovels, belt conveyors are ruled out and more manual intervention is required, but has to be kept at a minimum because of staff costs. Operational parameters As the average particle size of organic waste for a 5 kW or 2 MW plant will be similar, and 12% DM content is used as a maximum recommendation to ensure a reliable pumping operation across all scales of equipment, the equipment design informed by this research is representative of the proposed scale.


2.2 Digestion 2.2.1 Digester technology description The digester forms the main component in any AD system. It is a sealed vessel containing a wet slurry, up to 15% DM, which contains a wide range of anaerobic bacteria that live on the added feedstock. The most common operating temperature is the mesophilic range between 35-40°C, as this has been found to be an optimum environment for methanogenic bacteria. The digester needs to be able to maintain and conserve this heat as this is the main energy demand. The bacteria feed off a wide variety of organic materials reducing solids to liquids and gas. The digester facilitates this by allowing adequate contact between microorganisms and substrate, usually by mixing the contents. It requires feeding to maintain the microbial populations and an equal volume of digestate has to be removed to maintain a steady volume. Methane rich biogas is produced and captured from the biological process for use as a fuel source. The digestate contains all of the nutrients from the feedstock but in a much simplified form and consequently are much more available to plants when returned to the soil. 2.2.2 Digester technology selection There are four digester sizes/types proposed for this project, each of which has been sized to the needs of a particular project: the 1m3 IBC model (Site 1), a 2m3 Biogastronome (Site 2), a 6m3 Biogastronome (Site 3) and a 20m3 system (site 4), which was used for the Burford House food waste trials, a precursor of the Ludlow digester. All are described below except for the 20m3 digester, which is established technology not needing optimisation or scaling and has therefore not been included in the technology appraisal. 2.2.2.1 1m3 IBC digester - Site 1 The IBC digester is based on a low cost, widely available, standard, Intermediate Bulk Container. It aims to increase uptake of micro AD amongst community groups and individuals on a low budget. It has an integral pallet for a forklift and can be moved or stacked while full. There is a 200mm diameter gas tight lid on top with a 50mm threaded insert and a range of discharge valves with fittings for pipes and hose at the base. They are usually constructed of HDPE plastic surrounded by a zinc steel cage. This primary tank is then modified to become a digester. Insulation comprises a 100mm Celotex layer built around the tank with particular care given to joins where foil will be cut back to avoid thermal bridging, and expanding foam used to fill around the edges. The insulation is covered with a thin sheet material and finished with aluminium angle strip ensuring the digester is easy to clean and damage resistant. A 0.5kW solar PV array with battery storage and inverter will provide the energy required for heating, supplied via electrical resistance cable external to the plastic tank, so that heat can be distributed evenly aided by the cage. This is 240V AC system with an average demand of 75W and is thermostatically controlled with the option to use a timer to restrict power usage in the daylight hours if solar PV is available. Mixing is by recirculation of digestate from bottom to top for green biomass such as grass and the reverse for denser feedstocks such as maize or food waste. This can be done


manually with a whale pump or automated with the extra electrical load, which is relatively minor compared with energy demands for heating. Gas offtake is through a tapping in the digester lid carried by gas pipe to a 1.5m3 capacity gas bladder for storage, which operates at ~150mb - enough to become inflated. The bladder can then feed a combustion source directly or fit into further gas upgrade. 2.2.2.2 2m3 and 6m3 Biogastronomes - Sites 2 and 3 The 2m3 (Site 2) and 6m3 (Site 3) digesters are part of the Biogastronomy range of insulated GRP digesters, which are based on the successful German „Blacksmith‟ design. The digester body is double skinned fibreglass, insulated with shaped 50mm PU foam. It is designed to be sited outdoors, but where heat losses or security could potentially be an issue, the digester can be placed inside a structure, with the necessary ventilation and safety equipment installed. The smallest of the range is shown below in Figure 2.

Figure 2 - 0.2m3 Biogastronomy digester

As feedstock is fed in, digestate normally simply overflows. However, for certain feedstocks, a manual or automated auger can be fitted in order to remove sludge from the unit into the digestate tank. The Biogastronomy digester can operate with or without feedstock pre-treatment in order to demonstrate the cost-effectiveness of pre-treatment options. Feedstock can be fed directly through inlet augers, manually operated on smaller systems, and automated on larger ones. These digesters are both heated and mixed with their own independent simple mixing and heating control systems provided through a control box at the side, which has an e-stop easily to hand. The mixing arm incorporates a certain amount of shredding, so that a degree of internal maceration occurs. The arm turns very slowly and operates on a timer, which can be adjusted in the control panel. There are two heat exchangers which can be used on the same heating circuit or run from independent sources. A small biogas boiler can use the biogas to provide the digester with heat. Where biogas is needed for other purposes, an electric heater can be used. The standard heat exchangers operate at a maximum of 1 bar – where the heating circuit needs to run at a higher pressure, specialist heat exchangers can be provided.


2.2.3 Digester evaluation results 2.2.3.1 1m3 IBC digester - Site 1 Previous evaluation results Digestion trials at the University of Southampton carried out from November to March 2007/08 used a pair of 30L digesters operating in the mesophilic range (37C-40C) to examine the shock loading of food.

Table 1 - Results of digestion trials at the University of Southampton carried out from November 2007 to March 2008

Test conditions Results

Feedstock; kitchen waste including cooked food, vegetable matter, paper, some meat and fish. (Ave values; TS 225.6g kg-1, VS 200.0g kg-1, VS:TS ratio 0.885).

Feeding regime; 7 day fed batch liquor only removed.

Organic loading rate; batch 4-12 g VS l-1, daily 0.5 - 2.1g VS l-1 d-1.

Biogas quality; analysed on Soton‟s Gas Chromatograph; 55%-60%.

Volumetric biogas yield; 2.5 to 12m3 m-3 per week or 0.35 to 1.75m3 m-3 per day average.

While 4g VSg VS l-1 d-1 is high if fed every day, the digesters could cope with 12g VS l-1 d-1 and even 14.66g VS l-1 d-1 if given enough time to recover.

The trial was an extension of a batch fed ryegrass trial using a 7-day feed cycle, but as food digests quicker than grass, the feed cycle could be reduced to 3 days.

The digesters were stable for 6 months without any additions while the loading and gas yield increased.

It concluded that daily feeding is not necessary; feedstock can be delivered over any increment up to a week with the advantage that no partially digested material can exit aged less than the feed cycle length - an advantage for PAS110, which checks for residual methanisation. Stage 1 results Trials were conducted to determine the Coefficient of Performance (CoP) of the IBC digester, which has to be above 1 to indicate net energy production. Evaluating COP has given key insights into optimising micro digester design as heating is the greatest parasitic load. CoP is the ratio of energy produced compared with the energy needed to run the process. As digesters reduce in size their surface area to volume ratio increases, so that more heat is lost for a given volume as the scale reduces. The COP was estimated by measuring the heat loss while the digester is maintaining temperature.


Table 2 - Stage 1 results for IBC digester to evaluate Co-efficient of Performance (CoP)

Test conditions Results

The digester, with one layer of 40 mm expanded foam with 2 layers of foil, was filled with water and maintained at 38C over for 15 days and the electrical input monitored.

The nominal value of 1 volume of methane produced per day - per digester volume was used.

It maintained 38C with an average continuous input of 75W against an average temperature of 10C. This results in a CoP of ~5.

IBC cube proved capable of energy production at a relatively low cost.

It is intended that the insulation be doubled, therefore 75W may well be improved upon, requiring modest feeding to be energy positive. Electrical heating was chosen as the thermal bridge created when heat is transferred to the digester is minimised with an electrically insulated cable. Water exchange or heat pumps have the disadvantage of being good conductors of heat out of the digester when there is no heat demand. Our experience during the trial showed that mixing is a natural part of the feeding operation that occurs when digestate is manually removed and fresh feedstock added to the digester. If this is done daily, it sufficient mixing for the digester however, if feeding and digestate removal happen only 2-3 times per week, additional manual mixing is required.

Operational parameters for the heat loss trials were representative of the full scale while the gas yield and OLR should follow laboratory tests and are usually slightly improved upon at larger scale due to the reduction of particle size relative to the digester. 2.2.3.2 2m3, 6m3 and 20m3 digesters - Sites 2 and 3 The Biogastronome digesters were originally developed as 0.2m3, .6m3 and a 2m3 stand-alone units however, once site requirements were analysed, it became clear larger units would be required, so this study included 6m3 and 20m3 designs. The largest of these, the 20m3, is 100 times bigger than the smallest; the difference affecting a number of areas including feedstock handling considerations, gas use options and methods of digestate treatment, handling and use. This study therefore ensured that equipment system interfaces were taken into account identifying all necessary site-specific modifications to the digester. For example, where pre-macerated feedstock is used, the hopper design has been modified so feed can be pumped directly without heat loss into the hopper, with secondary overflow pipework going back to the digester should the feed pump fail and attempt to overfeed the digester. Heat loss tests identified a number of areas where losses were excessive and improvements could be made. These included improving insulation on the viewing window, hopper, main bearing and through-bolts. Additionally, heat exchangers were modified so that heat losses external to the digester could be minimised. Tests also showed that feeding rate parameters of all these digesters would be the same as those identified for the 1m3 IBC digester detailed in 2.2.3.1.


The original mixing system worked with a degree of shredding, but in one direction only. The improved mixing design incorporates fully automated bi-directional operation over a wider range of timings. The digesters will maintain their inbuilt temperature and mixing control system independent of the additional proposed control and monitoring system to ensure system failure does not occur. The performance co-efficient based on the heating energy parameters in 2.2.3.1 was found to be in the region of 3.78, 5.04 and 7.56 for the 2m3, 6m3 and 20m3 digesters, respectively. 2.3 Gas handling 2.3.1 Gas scrubbing technology description Effective gas scrubbing and pressurising raises the heating value of the gas and removes corrosive elements. To achieve this, percentages of carbon dioxide (CO2) and hydrogen sulphide (H2S) are removed to concentrations less than certain operational limits (prescribed by the gas use equipment suppliers). The project will demonstrate the benefits of biogas/biomethane as a high-grade source of energy and compatibility with a wide range of off the shelf equipment including gas burners and cookers, gas boilers, micro CHP units, gas refrigerators, compression into small cylinders (for street trader use) and biomethane vehicles, comparison of which will enable cost benefit analysis. The availability of robust, low-cost gas handling systems will allow operators to use gas equipment with confidence that warranties will not be nullified. The system comprises a number of primary components including:

gas scrubbing - de-sulphurisation, de-humidification, CO2 removal;

gas storage tanks - high & low pressure; and

safety items e.g. flame traps, condensate traps, pressure relief valves, etc.

While direct biogas usage is the simplest method available, biogas is not always produced at

the time or in sufficient quantity needed to satisfy the operator‟s needs. Incorporating a

variety of storage systems will help smooth out variations in the gas production and

consumption.

Gas scrubbing is required at three sites, with different biogas production capacities, gas applications and budgets influencing the technology choice for each system. 2.3.2 Gas scrubbing technology selection - Sites 2 and 3 Gas handling components at these sites include de-sulphurisation equipment, a bell over water gasholder with a simple water washing feature to aid CO2 removal, a CO2 recovery/storage vessel, a de-humidification vessel, flame trap and particulate trap. To maximise CO2 removal the proposed design will use:

temperature change to entrain and free CO2 from the water;

pressure change; and

(potentially) additives to increase CO2 solubility such as Monoethanolamine or MEA. As the digester operating pressure is limited to 7mb, the bell of the gasometer, which rises as gas is produced, is set to maintain pressure at <7mb.


Raw biogas passes through a desulphurisation chamber on the way to the primary 1.5m gasholder, arriving above the water surface. The gasholder is connected to a secondary 200-litre CO2 recovery gasholder, from which water is moved with a submersible pump back to the primary vessel with gravity. The pump sprays this water within the headspace of the bell, increasing surface area contact between the gas and water. CO2 from the biogas dissolves in the spray, which merges with the main body of water. This drains drains into the secondary vessel where the CO2 is released from solution and diverted to atmosphere or bladder storage. The pump in the main gasholder has a Venturi attachment that moves biogas from the headspace and introduces it approximately 1m under water through fine meshed spargers to reduce the bubble size. The bubbles rise to the headspace with CO2 gas dissolving on the way. Thus, CO2 removal happens via two simultaneous methods within the primary gasholder and this scrubbing loop is continued until the methane concentration increases to the desired level. An external pump then moves the methane rich gas to 1.5m3 bladder storage at moderate pressure below 100mb, which acts as a pressure buffer, allowing downstream equipment to operate at a constant or regulated pressure. Gas demand draws gas from the bladder through the dehumidifier and gas meter where the pressure is harmonised to 23mb (Site 2) or moved on to a compression system (Site 3). Gas storage is required overnight at both sites as usage will be during the day, so there has to be space for approximately 50% of the daily yield. At site 2, the 1.5m3 gasometer provides this storage and a scrubbing solution before the gas moves on to secondary storage. At site 3, storage is provided by a gas compression and cylinder storage system provided by Gas Fill Ltd. The Gas fill unit compresses gas to 200 bar and can either refill a vehicle overnight or send compressed gas on to storage in 89 litre cylinders. Equipment for H2S and moisture removal, already developed, tested and sold by a Canadian manufacturer (part of the LEAP partnership), will be re-packaged for use in the UK by GBBD LTD using locally available components. The desulphurisation technology is based on the dry adsorption process, which uses impregnated iron particles to remove sulphide from the gas phase to the solid phase. Housed in simple vessels, the method is used in numerous processing industries. Bell over water gasholders, as shown in Figure 3, are cost effective, simple in operation and widely used in micro AD. Successful demonstration of this low cost scrubbing solution will expand the range of micro AD applications to include standard gas appliances, avoiding the need for expensive equipment at a small scale.


Figure 3 - Typical simple gas storage vessels

2.3.3 Gas Scrubbing technology evaluation results - Sites 2 and 3 An initial literature review of the scrubbing technology required for the demonstration phase was undertaken by UCL students (Bai et al, 2013), a summary of which can be found in Appendix 4. All technologies reviewed reduced the environmental impact associated with emissions of polluting gases to acceptable levels; therefore, cost and ease of operation became the deciding factors. Research focused on re-packaging the desulphurisation and de-humidification equipment and scaling CO2 reduction and recovery equipment. While Site 3 will use upgraded biomethane for use in a dual fuel vehicle, the possibility emerged of trialling a micro PEM fuel cell CHP unit at Site 2 – see Appendix 4 for details. The unit requires gas delivered at a pressure of 23mb with a minimum 90% methane content and a combined sulphur limit for H2S and CO2 of 5 mg/m³ (3.587ppm). As the Stirling engine has already been successfully trialled with biogas by manufacturer Microgen, it was decided that scrubbed gas would first be used in a Stirling engine CHP unit at Site 2 to ensure the above gas composition limits could be reliably achieved, before moving on to using the fuel cell CHP unit. At Site 3, gas scrubbed gas will be compressed for use in a vehicle. A summary of research evaluating gas composition requirements for compression and vehicle combustion can be found in Section 2.3.5, with full details in Appendix 4. Table 2 below shows the initial target composition after scrubbing using the proposed equipment at both sites.

Table 2 - Biogas composition before and after scrubbing

% before scrubbing % after scrubbing

Methane (CH4) ~ 50 to 70% ~ +85%

Carbon dioxide (CO2) ~ 25 to 50% <20%

Water (H2O) ~ 1 to 5% by volume < 0.2 mg / Litre

Hydrogen sulphide (H2S)

~ from 100 to 2000ppm or up to 2% by volume

~ from 5 ppm

Other Hydrogen (H) ~ up to 5%, Oxygen (O) ~ 1.5%, Methyl mercaptan, Ammonia (NH3)

trace


The method of absorption and release of CO2 into the water is well known; we aimed to discover how much CO2 would be removed without incurring too much extra parasitic load. The graph below shows a decrease with increased temperature. The digester operates at ~40°C where digestate would be saturated with CO2 at <1.0g per litre, but as biogas moves to the storage gasometer (average ambient temperature 10- 15°C), the solubility doubles to >2g of CO2 per litre of water.

Figure 4 - Solubility of CO2 in water at atmospheric pressure versus temperature

The gasometer contains 1500 litres of water while the 2m3 digester is expected to produce between 1m3-2m3 methane per day with 450-900 litres CO2 (55%CH4 to 45% CO2 by volume). CO2 weighs approximately 2kg/m3 in the gas phase at ambient temperature. Therefore, between 900g-1800g of CO2 needs to be absorbed in a 24-hour period within 1500 litres of water. If the capacity of the water is 2g per litre, then 1500 litres has the capacity for 3000g CO2. While other factors may interfere with the absorption/release cycle, the above calculations show there is enough water in the system to absorb the required CO2, which will be regenerated in a secondary vessel. 2.3.4 Gas scrubbing technology selection - Site 4 Like Site 3, this site will upgrade biogas to biomethane for vehicle use however, as biogas production is greater here than at the other sites, a more appropriate scrubbing solution has been scaled down from equipment previously produced by Methanogen.


Figure 5 - Larger-scale gas scrubbing system for scaling

The primary elements of the gas scrubbing system are 3 cylindrical towers of 150mm diameter constructed out of ABS pipe, which serve the following purposes: 1. & 2. Water pumping columns (Items 13 & 14). Alternately force rising and falling

columns of water to act as pumps, compressing raw biogas to an intermediate pressure. The system is driven by the primary water pump (WP1), which draws water from the falling column and forces it into the rising column. The flow of water is controlled by a rotary changeover valve (Item 4) manufactured from PVC which is actuated by a pneumatically operated piston (Item 5). This piston is signalled to change over when the rising column reaches the top of the cylinder, detected by a capacitance probe (Item 31). In the top of each column is a floating ball valve (Item 16a), which ensures no water exits from the top of the column into the intermediate pressure biogas cylinder. Two non-return valves (Item 16) in the top of each column allow gas to be alternately drawn in and then expelled. Raw biogas is drawn directly from the gasholder via the scrubbing chamber.

3. The third chamber (Item 6) is a buffer store to receive the intermediate pressure gas

from the pumping system and hold it for injection into the next stage. 4. Scrubbing tower (Item 7). When the buffer store (Item 6) reaches a set pressure,

a pressure switch (Item 35) detects this and starts the secondary pump running, opening a solenoid valve to inject gas into the base of the scrubbing tower. The secondary pump draws water from the water holding tank and pumps it into the top of the scrubbing tower, which runs at a fixed pressure. The full gas flow is allowed to rise up the tower, through the filter media (which fills the tower) while water is allowed to fill up to approximately 90% the height of the tower. External to the tower and parallel to it is the water stilling tube, which senses the true water level in the tower, so this can be detected by an immersion probe (Item 10) mounted in the top of the stilling tube. The actual liquid level and detection of it takes place within a transparent sight glass tube at the top of the stilling tube.

When the water level in the scrubbing tower reaches the detection probe, a water solenoid valve opens releasing water back to the water holding tank. This solenoid


valve is parallel to a fixed orifice (Item 12), which allows a constant rate of flow back to the water holding tank. During commissioning, the orifice size is adjusted to optimise the cycling of the water release solenoid valve. This ensures that, during normal operation, the water level in the tower remains virtually constant, with minimal operation of the solenoid. The gas exits from the top of the tower and the water exits from the bottom. The flow rate of pumps WP1 and WP2 can be adjusted and, in particular, WP2 increased in speed and pump WP1 reduced, to maximise the absorption of the carbon dioxide.

5. Scrubbed gas buffer store. The gas from the scrubber flows through a pressure

regulating valve (Item 6), designed to maintain constant exit pressure from the scrubbing tower, before entering the scrubbed gas buffer store or gas holder. It is essential to maintain a constant back-pressure on the scrubbing tower to ensure constant gas flow rate to maximise CO2 scrubbing. Gas in the buffer store will accumulate up to the maximum level, upon which a pressure switch (Item 35a) will shut down the whole process. From (11), the wet gas passes through a chiller unit. This could be a proprietary unit or manufactured from a series of gas bottles. Ice will gradually collect and will have to be defrosted. After a period of operation, the system will have to be shut down, allowed to defrost, and water expelled back to the gasholder by opening valves.


Figure 6 - Scrubbing tower biomethane upgrading system

The system can be switched on and off by pressing a start button. The primary pumping system switches off automatically when the pressure switch P2 (Item 35) reaches the set pressure. The system can also be triggered automatically using a signal from the gasholder indication high level, shutting down automatically on low gasholder level (low gas pressure). The outlet from the scrubbed gas buffer store is via a pressure-reducing valve, which reduces the outgoing pressure to typical mains gas pressure to feed into the Gas Fill compression unit. 2.3.5 Gas handling evaluation results - Sites 3 and 4 As only slight scaling of established technology is required at Site 4, research focused mainly on gas composition requirements for vehicle combustion and compatibility with the Gas Fill compression unit, which will be used at Sites 3 and 4. A summary of the findings are listed below:

the compression flow rate needs to be 2 scmh;

to satisfy combustion requirement the CO2 level in biomethane should be less than 10%;

to satisfy high pressure compression, the CO2 levels should be less than 40% for ambient temperatures no less than -10 °C;


a water dew point of less than -25 °C at normal ambient temperatures is required and lower still for severely low ambient temperatures. A commercial absorbent gas dryer will normally achieve a dew point of -40 °C; and

compression takes place in three stages with a maximum delivery pressure of 250 Barg.

Full findings, including graphs, can be found in Appendix 4. 2.4 Digestate handling 2.4.1 Digestate handling description The sludge or digestate leaving the digester is >90% of the input volume of feedstock. Theoretically, this whole digestate can be spread on the land as a fertiliser without further treatment (i.e. supernatant and solids together) with some advantages. However, as fertiliser is generally applied seasonally, digestate has to be stored until application. Post-treatment to separate solid and liquid fractions can lower the storage cost, thereby increasing safe storage time. Other advantages associated with post treatment include:

Reduction of biodegradable organics associated with bad odour (Abdullahi et al., 2008).

Making wider distribution/applications possible, particularly in urban areas as separation

produces:

- fibre, which has excellent soil conditioning and water retention properties, is high in

phosphorus and other nutrients and promotes root and shoot growth, and

- liquid, which has high levels of available nitrogen and promotes turf growth and food

growing.

The solid organic fraction can be used directly on land or matured in conventional compost bins. As vermiculture is already well practised on most community composting sites, it may be possible to integrate existing systems for further processing of digestate fibre. 2.4.2 Digestate handling technology selection Figure 7 shows a schematic of the proposed anaerobic digestion process (excluding gas use), with the green dotted lines highlighting the proposed digestate treatment. Digestate is either gravity fed or pumped into the digestate processing tank. At this stage, there is still the possibility of off-gas production, so a small amount of biogas could be recovered and sent on to the gas scrubbing system.

Figure 7 - AD Schematic - Green dotted line shows digestate post-treatment system


After leaving the digester, digestate will be dewatered into two parts; a liquid fraction (liquor) and a solid fibrous fraction (fibre). For ease of handling, it is easier to separate the liquid fraction from the solids.

Figure 8 - Water press to separate digestate fractions

An extremely simple, highly effective pressing system using mains water pressure will used to extract high levels of liquor from the fibrous fraction. This equipment has been transferred from other industry sectors, but is well suited to the micro AD community. The press is operated by top-filling the void between the outer screen and the internal bladder with digestate. After loading is completed, the bladder is inflated with water to apply pressure to the digestate. Digestate liquor is separated by force through the screen and the solid fraction remains inside awaiting removal. This is a batch process requiring manual unloading of the fibre. A post-digestion vessel will store the liquid fraction after separation, transferred by a liquid scavenge pump where gravity is not an option. 2.4.3 Digestate processing technology evaluation results

While the water-press technology was evaluated for the larger sites 3 and 4, with daily fibre yields between 15-50 kg respectively, research identified the „sedimentation process‟ as a more cost-effective alternative for the smaller sites 1 and 2, each with daily fibre yields of 2-3 kgs. Sedimentation tank – Sites 1 and 2 This simple technology has been transferred from small-scale vegetable oil processing for removing sludge (cell tissue) and can be implemented using low-cost, recycled settling tanks. They separate the low viscosity liquid fraction by means of gravity and have a steep inclined conical bottom with a large diameter valve to discharge the higher viscosity sludge fraction. An additional drain valve will be added for digestate liquor recovery in a storage vessel. Where possible at these sites, gravity will be utilised to minimise costs and complexity, otherwise simple hand pumps will be used. This technology could also be utilised on larger systems, although with some disadvantages, such as the requirement to protect the vessel


from frost / winter conditions and increased labour time removing the settled sludge and floating fibre. Water press – Sites 3 and 4 To enable successful „technology transfer‟, the press has been modified to suit the new application. The factors determining the new layout/orientation include the output position and the space/footprint restrictions, which is likely to be an issue at further urban sites. A horizontal mounting arrangement was investigated to help reduce the loading height from the digester discharge and assist manual loading of the unit, however the liquid scavenging arrangement was compromised for the minimal height gain. The press received additional modifications including the addition of an outer wrapper to help minimise odours, and a small buffer/diverter valve to the digester input, diverting the digester flow during manual removal of the solid fibrous fraction and preventing overflow. Manufacturers of this equipment quote its capacity based on the dimensions of the „pressing drum‟, rather than the actual „working volume‟ available, which is approximately half that of the drum. Once testing is underway at Site 2, (before the WRAP demonstration period) a more accurate figure will be gained by subtracting the bladder volume from the drum volume. Meanwhile, a press with a working volume of approximately 150 litres has been chosen to provide a balance between minimisation of batch change-over (operator costs), unit costs and footprint, Daily digestate production at sites 3 & 4 is approximately 150 and 500 kg/day respectively, of which we can assume a 10% solid fraction, i.e. 15 and 50 kg/day. Although the selected press capacity is less than the digestate production at Site 4, much of the liquid content is estimated to pass through the drum before pressing commences. Experimental testing was carried out on the bladder pressurisation to cut down water consumption required for each operation. To that end, the possibility of replacing water with liquid digestate (to fill the bladder) was researched, with no detrimental effects. The scavenge pump capacity was examined to investigate the possibility of locating the liquid digestate storage vessel above the press, thus utilising the same platform arrangement for storage / pressing operations. While not necessary for sites 3 and 4 where space is less restricted, it may be a useful option for sites where the footprint needs to be minimised.

A high limit switch was added to the post storage vessel, which communicates with the pre-digester transfer pump to prevent overfilling, i.e. if the post digestion vessel is full, no fresh feedstock will be transferred into the digester. This allows the digester to keep producing biogas.


2.5 Monitoring and control system 2.5.1 Monitoring and control system description Producing biogas from the potentially challenging substrates of municipal and commercial food waste could easily lead to process instability without control measures in place. Inappropriate feeding can cause accumulation of intermediate compounds resulting in biological imbalance and eventually collapse, with a burdensome restart of the digester and subsequent economic losses for the operator. Many examples of successful automatic control systems for AD exist both in academic literature and at many large-scale plants, providing blueprints for scaled micro versions. The control system takes inputs from sensors, using them to assess the operation of the plant and the state of the biological process, make decisions about the loading rate and communicate the status and any errors to the user and/or a central control system. The aim is to enable the safe, optimal and stable operation of the plant without requiring the immediate user to be an expert. Under normal conditions plants will operate mostly automatically however, expert technical help is still necessary if faults are detected, with data from sensors continuously screened and validated to check for errors and inconsistencies. Best practice dictates that monitoring is kept separate from control, so that discrepancies between the two systems can highlight potential sensor failures or systemic issues. With the increasing availability of robust, reliable and cheap sensors, programmable logic controllers (PLC) and Ethernet bridges, it is becoming viable to have process monitoring and control in a variety of situations where previously this would have economically unfeasible. Moreover, the ubiquity of Internet access enables a range of novel approaches in AD management especially relevant to small-scale networks, for instance:

rapid intervention by an expert in case of unknown process conditions or hardware faults;

leverage of knowledge from the operational data of many similar digesters (data mining);

remote updating of the diagnostic rules when new knowledge about the process becomes available; and

optimising the transport of waste/residues to the AD sites, depending on the state of the digesters.

2.5.2 Monitoring and control system technology selection A 3-tier control system was chosen with each tier assigned a particular role in the operation of the AD plant as described below:

Basic operation – Controls the everyday running of the plant and consists of mainly basic sensors for safe operation and protection of the plant from damage. This system monitors the temperature of the digester and detects faults with the subsystems e.g. stirrers, heater, feed pump, tank overflows.

Expert controller – A rule-based expert system analyses the state and trend of the biological process according to some easy to understand classifications: hydraulic overload, organic overload, organic under load, presence of toxins; trend estimator: degrading, stable, improving etc. The expert system takes this information along with other inputs such as expected biogas demand and the current biogas storage, uses the feeding pump as the main actuator to maintain a stable and efficient process.


Remote supervision – The control system has an Ethernet interface, which allows remote connections through the Internet. Therefore it is possible to collect and store operational data from several plants, and leverage the knowledge about the process behaviour under similar conditions (data mining); this also allows an informed evaluation of the impact of the technology (e.g. total waste diverted from landfill, total energy produced from biogas) by policy makers and financers. Remote experts will have access to the local microcontrollers and could eventually update the diagnostic and control rules, and the classification and composition of available substrates. Also, quick alerts would reach the managing company in case of faults, required services (such as calibration) or unknown states detected.

The main components include sensors and electronic hardware used to process signals before their output, which include a user and internet interface, control actuators and local and remote alarms. The hardware combination is designed to be modular and scalable for the various micro AD systems proposed in phase 2. Software design includes three main elements; validation of sensor data, the monitoring system/external interface and the control system. Data from sensors will be used alongside qualitative and quantitative feedback from site operators to evaluate the overall performance of the micro AD network in terms of process stability, mass, energy and carbon balance and safety. 2.5.3 Monitoring and control system evaluation results The feasibility assessment consisted of three main parts:

The control system was developed based on simulations of the AD process and peripheral components (pumps, tanks, heaters, mixers) in Simulink/MATLAB (Mathworks, USA) using tools already developed by UoL (University of Leeds) researchers. These tools were used to design and benchmark different control options in order to select the most promising configurations for the proposed scenario of a network of small-scale digesters fed with urban wastes. At this stage it was assumed that sensors could reliably and accurately detect their respective physical quantities.

A desk based study collected information about the availability, specifications, limitations and cost of the required sensors for the selected control configurations. This resulted in the selection of the most appropriate sensors for the prototype to be built in phase 2. During this stage, based on the limitations of some sensors, adjustments were made to the previous simulations in order to more accurately assess the suitability of the control configurations.

The final hardware selection was performed by Aleka Design in order to produce a hardware design. This includes a microcontroller, I/O modules, a graphical user interface, remote communication interfaces and actuators. This design along with the selected sensors will result in final design (see Technical Construction File).

The key challenge was in maintaining a balance between costs and optimal operation. Costs were kept down by determining the minimal implementation required for sufficient functionality.

Sensors/hardware A number of options were explored in terms of the control laws, and the available control actuators (feed rate, temperature, mixing etc.), and a range of sensors investigated, with particular focus on biogas flow and composition and pH (the main performance and stability indicators in AD). The primary criteria in sensor selection were to:


access parameters which allow efficient and cost-effective monitoring;

be able to withstand the potentially corrosive environment of an AD plant; and

allow relatively uninterrupted operation and low maintenance.

The final selection of electronic hardware modules resulted in a design which will be further developed in phase 2. The design consists of a PLC, an internet interface and a dedicated controller module which will allow direct use of the developed Simulink controllers. The final design of the monitoring and control process is outlined in detail below. Validation and monitoring The first processing step performed on the sensor output signals by the CuBloc PLC is validation, involving checking sensor data for the most frequently generated errors such as missing data, out of range data and constant measurement values. The validation method uses a confidence based scoring system of the sensor signals whereby an error state is triggered if the confidence falls below a certain threshold. After validation, the system manages further processing of the sensor signals and their transmission via the internet and user interfaces. The I/O Bridge makes a tiered external interface with the CuBloc PLC possible, allowing both secure access to the full control and monitoring system and public access to a limited set of data for e.g. webpages and smartphone applications. The monitoring system design involves direct transmission of appropriately averaged sensor outputs and derivation of more complex data from multiple sensor signals. The sensors have been organised to allow a variety of derived process indicators, calculation of cumulative waste addition, mass/energy/carbon balance, cumulative biogas/biomethane production, organic loading rate, specific biogas and methane production. Example algorithms to calculate these have been given in Appendix 3. A further output of the monitoring system is an assessment of the qualitative „health‟ of the digestion process1 giving the user a non-numerical assessment of the AD process based on several sensor inputs e.g. stagnant, shortage, acidifying, pre-methanisation, overload etc. Control system design A control system capable of adjusting the feedstock-loading rate was designed based on three sub-systems. These interact to meet a particular expected biogas demand and maintain the storage of biogas at its midpoint to account for variation in demand, whilst protecting the biological process and ensuring smooth and continued plant operation. The biogas demand in this case is an input to the control system, coming from either the user if they are able to specify their (e.g. daily) biogas demand, or from the Internet interface. The overall control design is shown in Figure 8 with a full description in Appendix 3. The final cascade of the expert controller uses a pH based proportional controller to drive the final control gain as suggested by Liu et al (2004), however it is thought that a better immediate indicator of process health might be biogas composition, as well as coming from a generally more reliable sensor. This will be explored in Phase 2 along with further optimisation of control system parameters based on operational data collected.

1 Implemented by a fuzzy logic based algorithm (Murnleitner et al 2002)


Figure 8 - Design of control system

The integration considerations between each sub-system and the monitoring and control system were then identified and assessed. In addition, potential sites were identified and assessed, and a suggested digester system specification drawn up.


3.0 Site selection and evaluation 3.1 Site selection During LEAP‟s previous Technology Strategy Board micro AD feasibility study the team identified twelve potential host sites. Details in Section 4.2 of the report can be downloaded here: https://connect.innovateuk.org/c/document_library/get_file?uuid=f87d1192-edfe-4885-9067-f93b99defa97&groupId=6764506 These sites were reassessed in light of this study to determine which might be included in the proposed network for the WRAP DIAD II demonstration phase. The criteria used to assess the suitability of sites in hosting a micro AD system can be found in Appendix 1 Of the original twelve, two sites were selected - The Calthorpe Project and Alara Wholefoods Ltd - for the demonstration phase based on cost, range of biogas and digestate applications and commitment to the project – see Appendix 1. The majority of sites were rejected due to costs exceeding the budget available for this project or inability to distribute/utilise digestate. The sites selected were chosen primarily for their ability to utilise all AD outputs and demonstrate the full range of biogas applications within the budget available, as well as their commitment to the project. We assessed two other sites for suitability. 1. Camley Street Natural Park was selected as it currently hosts LEAP‟s pilot system,

which can be upgraded for the demonstration phase and is in close proximity to the other sites.

2. While Loop Recycling Ltd were not included in our original proposal, their

commitment to sustainability and willingness to largely self-fund their own system (should it prove viable through our study) led us to consider their inclusion. The study in turn will benefit, by comparing economics across a wider range of system capacities. Loop is 6 miles from the other sites.

The project will seek to involve two more micro AD systems remotely as part of the monitoring and control evaluations by funding their monitoring and control systems only. This means, while not having to invest in the whole systems, the project will gain valuable additional data to compare alongside the four sites identified above. The first of these systems is manufactured by Off Grid Gas, a Canadian micro AD company; part of the LEAP partnership. The second is manufactured by Eco Comply, who have recently developed a PAS100 compliant scalable micro AD unit. While not part of the localised network, these additional data contributors will help expand the picture gained through the evaluation process.

https://connect.innovateuk.org/c/document_library/get_file?uuid=f87d1192-edfe-4885-9067-f93b99defa97&groupId=6764506



Figure 9 - Proposed network sites for the Phase 2 demonstration

The table below describes in detail the four sites chosen for the Stage 2 demonstration network including Loop Recycling, who will make a decision on whether to proceed following the conclusion of this report.

Table 4 - Details for selected sites

Site SITE DETAILS

1. The Calthorpe Project

The site An inner city oasis where people grow and learn together taking care of each other and the environment, this community garden and centre has a kitchen, workshop spaces and a well-established food growing and composting area. They offer volunteering opportunities in food growing and gardening as well as outdoor, creative, social activities for children. The Calthorpe are willing to raise match funding to augment WRAP and LEAP funding to ensure infrastructure needs are met and to support AD–related enterprise development, with established links to various charitable funding bodies. Feedstock supply The Calthorpe are interested in managing a local waste collection enterprise and have already been approached by several local businesses (coffee shops, pubs, the People‟s Supermarket) to see if they can take their organic waste – some of whom are even prepared to bring in their waste. There is also some green waste generated on-site, which could help the micronutrient balance of the feedstock, which will largely be catering food waste. Community enterprise opportunities The Calthorpe are committed to operating their own digester and developing AD-related enterprise opportunities. So far, they have sold some produce to the People‟s supermarket. With the addition of a larger polytunnel, AD-generated heat and CO2,


this commercial activity could be increased to provide local employment opportunities. Future plans include a rebuilding the centre to include a café, expanding enterprise opportunities into catering and expanding the market for produce grown on-site.

2. Camley Street Natural Park

The site An Environmental Education Centre located within an inspiring 2-acre urban nature reserve in the heart of Kings Cross, London, whose Visitor and Information Centre serves a range of functions including London Borough of Camden „Small Step‟ sustainability HUB, hub site for London Wildlife Trust volunteering operations, varied schools (KS1 and KS2 on Biodiversity and the environment) programmes and environmental community events and arts programmes. On-site activities include recycling green waste and dry recyclates, food growing, healthy eating programmes, rainwater harvesting, composting training for schools and community groups, provision of compost and liquid feeds to visiting public. They also have relationships with developers and construction firms to recycle some of their construction waste products in their volunteering programmes. Feedstock supply The Centre is responsible for maintaining the green banks along the canal from Camden Town to Islington tunnel, approximately a 3km stretch. As well as being able to collect green waste from these sites and their own 2-acre site, they will also collect pondweed from the canal and their own wildlife ponds. These sources will help balance micronutrients augmenting locally collected food waste, which will comprise at least 75% of the feedstock. Contacts from a previous survey assessing feedstock availability in the area will be used to establish a supply within a 1-mile radius. Community enterprise opportunities Using the centre‟s existing bicycles and trailers, a small local food waste collection enterprise will be piloted with income from collection fees, green tariffs and a small charge for liquid fertiliser. They are currently fundraising to rebuild their centre and hoping to incorporate a café. Like the Calthorpe, this would expand their enterprise opportunities and provide a market for food grown on-site using digestate. Their AD system would be incorporated into educational programmes addressing air quality, recycling, climate change and renewable energy generation. Also in the next 2 years, a footbridge is planned to link the Park with Kings Cross Central, the largest development site in Europe, increasing accessibility and exposure of the technology to a wider audience.

3. Alara Wholefoods

The site Established in 1975, Alara‟s commitment to sustainability and health has led them to manufacture high quality organic wholefoods. They have a factory and successful wholefood shop, both close to Kings Cross. Feedstock supply They will combine their own organic waste including 350kgs/week dry cereal grain (currently collected and taken to an AD plant approximately 60 miles away) and 85kgs green non-woody waste, with locally collected food waste. Their integral involvement in the development of the Camley Street Neighbourhood Forum will enable them to easily form relationships with the surrounding residential area and local food manufacturing units to secure feedstock, setting a framework for local food waste management.


3.2 Site evaluation results Below, results from the site evaluations are summarised showing system configurations and site ability to utilise AD products. Research led to refinements in the original system designs, in some cases, with staged approaches to gas applications evolving for a more tailored approach.

Table 5 - Summary of site evaluations

Site System design modifications

1. Calthorpe Project

System proposed 1kW solar PV array, 1m3 digester, 1.5m3 gasholder polytunnel, greenhouse and raised beds), 1m3 digestate processing/storage, monitoring and control system, space heaters. Utilising AD products Digestate will be used extensively on-site as well as there being potential for distribution to the local community. Digestate fibre would also be utilised by their on-site food growing groups.

Community enterprise opportunities The proposed polytunnel will operate on a commercial basis to grow tomatoes, a high nutrient crop, creating local training and employment opportunities in the process.

4. LOOP Recycling Ltd

The site Loop have been established for 15 years and is a one-stop shop for London based recycling. They relocated recently, but plan to remain on the new site for the long term. Passionate about the environment, they are and keen to explore ways of benefitting the environment and making economic savings in order to bring down costs for customers to encourage more recycling. One of the main barriers to food waste recycling is cost due to its weight. They currently transport organic waste 60-70 miles to an AD plant. Feedstock supply They collect 400kgs organic waste daily but could easily expand this. The waste comprises 60% mixed food waste from commercial kitchens, 20% spent grain, 15% fruit and veg and 5% bread. They would be able to target certain waste streams if necessary to optimise the AD process. They operate 5 days p/w so feeding regimes would need to take this into account. Miscellaneous

3 phase electrics;

development could take place anytime except during busy holiday periods (Easter and Xmas);

roof space for solar installation available;

main concerns about AD – financial risk, tech readiness, safety and stability of end market (digestate);

not in a hurry and willing to wait until right option emerges; and

interested in exploring the possibility of using biogas for cooling at this scale.


Currently, propane cylinders are used at £74 p/month between November and March to heat 2 polytunnels. This would be replaced with biogas, enabling them to also heat a greenhouse and raised beds. The system will be established to run over the winter months with the advantage of raw biogas adding CO2 to the atmosphere when burnt in space heaters to further support plant growth. During warmer months the system may be relocated to produce gas for hot water and cooking in the main building (as water heating has been identified as a need). The centre can then decide which application is most useful or invest in a second digester so both applications are covered. Should the digester remain in the food growing area, gas may be used in a gas refrigerator to keep harvested food fresh during the summer.


System proposed 0.6m3 pre-processing unit, 2m3 digester, 2 x 1.5m3 gasholders, gas scrubbing (CO2, H2S and moisture) unit, pressure regulator, micro CHP unit, digestate settling tank, digestate storage, monitoring and control system. Utilising AD products The Centre will utilise electricity and heat generated from the biogas for its own energy consumption, feeding surplus electricity to the grid. The possibility of trialling a micro PEM fuel cell CHP unit has emerged (under EU funding), which would be evaluated by a Brunel University PhD student. In light of this, the plant will be initially commissioned with a simple gas scrubbing system using a Stirling engine CHP unit. Once established, improvements to the scrubbing process will aim to produce biomethane to fuel cell specifications, see Appendix 4. Heat will be used for space and water heating, and indoor horticulture/food growing activities. CSNP is the local lead for Camden‟s 126 Capital Growth‟s food growing sites. They can act as a digestate distribution channel for this network as well as the other London Wildlife Trust sites in North London, which they coordinate. Excess electricity will be exported to grid. In the summer, biogas will be used for gas refrigeration. Digestate separation will take a simpler, lower cost form (settling tank) than originally planned (water press) due to space and budget considerations.

3. Alara Wholefoods

System proposed 6m3 digester, 4m3 digestate storage and water press separation unit, 5m3 gasholder, upgrading unit to biomethane (H2S, moisture, CO2 scrubbing), compression to 12 and 200 bar (Gas Fill unit), biomethane. Utilising AD products Most of the biogas will be converted to biomethane to help run a dual-fuel vehicle for their new Local to London food deliveries. The gas compressor will also compress gas in small cylinders suitable for greenhouse heating and street market trader use. A service may be developed by CbD collecting food waste and dropping off cooking fuel to street traders. Alara will utilise much of the digestate they produce using a piped irrigation delivery system in the orchard, community garden and vineyard created


from derelict land around the factory. The proposed polytunnel will also utilise a range of AD products including digestate and CO2 to enhance plant growth, and biogas to heat the space. This site also has potential to distribute digestate in other ways:

the local Forum involving residents and businesses are currently planning a greening programme, which could utilise the product;

Alara‟s work with the North London Waste Authority developing their site as a compost hub, means that over 50 local gardening groups come to collect compost, with this figure expected to rise. Surplus digestate liquor from all network sites could be brought to Alara and stored in a dispensing tank for collection by these same gardening groups; and

Alara is headquarters for the London Orchard Project, who work with Londoners and local organisations to plant and harvest fruit trees across the city, thus forming another distribution channel.

Simple de-packaging will take place on specially designed infrastructure to deal with feedstock from a neighbouring factory. Analysis of the onsite feedstock composition (mainly dry oats) resulted in a plan to distribute surplus oats to other sites to help balance micronutrients and maximise gas yield across the network.

4. Loop Recycling Ltd

System proposed Mill, pasteurising tank and transfer pump, 20m3 digester, 20m3 digestate storage and separation unit, 5m3 gasholder. Biogas option A - upgrading to biomethane (H2S, moisture, CO2 scrubbing), compression to 200 bar (Gas Fill unit), biomethane used for waste collection vehicles. Biogas option B – H2S and moisture scrubbing, 6kW biogas CHP unit. Utilising AD products The preferred use for biogas would be upgrading to biomethane for use in waste collection vehicles. Loop have:

5 x 3.5 tonne vans;

3 x Lutons with boxes;

2 x cage tippers; and

1 x 7.5 tonne lorry.

Should this option prove economically unfeasible, a second option identified would involve running a biogas CHP unit supplying electricity and heat for the warehouse and high temperature bin washing equipment. Excess electricity will be exported to the grid. Excess heat will be shared with neighbouring business units. They would need support to establish a market for digestate but have the capacity to transport it to nearby farms, golf courses etc.


4.0 Network evaluation and cost benefit analysis 4.1 Inputs and outputs including energy balance and mass balance, process flow and/or

other technical diagrams At this stage of the project, it is not possible to do detailed mass/energy balance calculations, but a basic analysis is provided in Table 3 below.

Table 3 - Basic mass balance for the proposed sites

Parameter Unit Site 1 Site 2 Site 3 Site 4

INPUTS

Food Waste - Demonstration site Kg/yr 7,300 14,600 43,800 146,000

Total Input Kg/yr 7,300 14,600 43,800 146,000

PARAMETERS

Food Waste: DM % 24% 24% 24% 24%

Food Waste: oDM % 91% 91% 91% 91%

Food Waste: specific methane yield m3/ToDM 380 380 380 380

Food Waste: methane:biogas % 60% 60% 60% 60%

Methane Yield m3/tonne FM 82 82 82 82

Biogas Yield m3/tonne FM 137 137 137 137

OUTPUTS

Food Waste: Methane Output m3 602 1,204 3,611 12,038

Food Waste: CO2 Output m3 401 803 2,408 8,026

Food Waste: Biogas Output m3 1,003 2,006 6,019 20,064

Food Waste: Methane Output kg 430 860 2,580 8,599

Food Waste: CO2 Output kg 788 1,576 4,729 15,764

Digestate - total kg 6,082 12,164 36,491 121,637

Total Output kg 7,300 14,600 43,800 146,000

Because the method of separation can vary, the digestate could be further divided down into „fibre‟ and „liquid‟ portions. On an analysis of the Ludlow digester, Banks et al (2010) found that, on a wet weight basis, the fibre weight was approximately 1% of the liquid weight and it could be assumed that similar results could be obtained here; however, the type of separation process will ultimately determine actual results. It is also recognised that a proportion of the biogas produced will contain water vapour, sulphur and possibly other substances. Again, analysis at the Ludlow food waste digester showed that, on a wet weight basis, 2% of the biogas consisted of water vapour, with carbon dioxide making up 61% and methane making up 37% of the rest. Sulphur and other substances were not analysed in this particular Banks model and is also not included here. It is envisaged that process water can be added to the systems which have front-end processing. This liquid could come through recirculation from the anaerobic digestion process itself, or rainwater could be collected and used, in order to reduce operating costs. Additionally, a certain amount of water top-up will likely be required for the scrubbing system, but this has not been included in this analysis as part of the demonstration will be to optimise and model these parameters.


Table 4 - Energy balance of proposed systems

Parameter Unit Site 1 (1m3)

Site 2 (2m3)

Site 3(6m3)

Site 4 (20m3)

ENERGY PRODUCED (GROSS)

Food Waste: Methane Output m3/yr 602 1,204 3,611 12,038

Energy value of methane MJ/yr 21,488 42,977 128,930 429,766

Energy value of methane kWh/yr 5,969 11,938 35,814 119,379

ENERGY REQUIRED

Heating energy kWh/yr 876 1,051 3,942 1,752

Mixing energy kWh/yr - 88 219 438

Digester sub-total kWh/yr 876 1,139 4,161 2,190

Pre-treatment energy kWh/yr - 1,683 - 1,155

Digester total kWh/yr 876 2,822 4,161 3,345

Pasteurisation energy kWh/yr - - - 22,002

Biomethane upgrading & compression kWh/yr - - 8,330 27,768

Separation kWh/yr - - 378 1,261

Total system energy used kWh/yr 876 2,822 12,869 54,376

Excess of energy created over use kWh/yr 5,093 9,116 22,945 65,003

Percentage of energy used / created % 14.7% 23.6% 35.9% 45.5%

It can be seen from Table 4 that the simplest system, the 1m3, has the lowest parasitic load, i.e. that required for heat only. However, this tank must be manually mixed, which is likely acceptable at this size, but possibly problematic with larger volume digesters. A large proportion of the energy required for Site 2 is due to the maceration, heating and feeding with the pre-feed tank, as well as the gas upgrading element. Sites 3 and 4 use a significant proportion of their energy in biomethane upgrading; however, in the case of Site 4, the removal of pasteurisation would improve the system to 27.1% and further removal of pre-treatment and separation would improve the parasitic load further to 26.2% and 25.1% respectively. Although feedstock is pre-heated and pre-pasteurised in systems 2 and 4 respectively, there will still be an element of heating required for the digester itself and the above model assumes a „worst case‟ scenario based on factors of heat losses due to the surface-area-to-volume ratio of these small systems and the inherent heat losses therefrom. Further insulation can improve this, or siting within an area such as a greenhouse means that the heat losses are at least usefully employed. Additionally, although outside the scope of the capex of this project, electricity consumption could be offset through the addition of solar PV or solar thermal to the systems; however, the economics of this would have to be assessed on a case-by-case basis. Figure 10 illustrates a simplified process flow for all the digester systems. Note that numbers in brackets refer to the individual systems, as each system contains differing components.


Figure 10 - Amalgamated process flow

4.2 Comparison with „business as usual‟ and other technologies In light of changing legislation and rising landfill charges, micro AD offers a sustainable solution for waste producers looking to save waste management, energy and/or fertiliser costs. A 2012 “What if” analysis2 (see footnote below) compared economic, social and environmental impacts of a local distributed micro AD network versus a large centralised AD plant. Although specific to the scale of that study, the comparisons bear relevance to this report. The table below compares the social and environmental impacts applicable to any scale of micro AD network with those of large centralised plants.

2 See section 4.1 at https://connect.innovateuk.org/c/document_library/get_file?uuid=f87d1192-edfe-4885-9067-

f93b99defa97&groupId=6764506




Table 5 - Local micro networks vs large centralised plants

Small local networks Large central plants

Network comparison

Organic waste collected locally using low/no carbon methods

Waste transported an average 20 - 60 miles for processing

Avoided waste transport costs, CO2 emissions and air pollution

Simple planning process, regulatory exemptions available

Complex planning and regulatory requirements

Reduced start up timescales and costs

Local community ownership and enterprise opportunities e.g. urban agriculture and local food waste collections

Corporate ownership

Stronger local economic and energy security, community empowerment and increased resilience to food and fuel prices rises

Small footprint, suitable for siting in urban areas

Large footprint and complex infrastructure requirements

Reduced capital (infrastructure) costs, greater flexibility in siting plants

Digestate used locally for intensive urban agriculture and greening projects

Digestate transported for farming agriculture

Less transport of imported products, fertiliser replacement value of £83/ha,3 enhanced local environment through increased greening, reduced water usage

Good flexibility if food waste volumes fluctuate over time

Inflexible to reduction of feedstock inputs4

Enables waste minimisation over time5

If one AD process fails others continue to process

More vulnerable to total system failure6

Less overall downtime as individual plant malfunctions more easily accommodated

Control and monitoring system comparison To test the performance of the control system relative to the „business as usual‟ a Simulink model of the digestion plant and control system was created.7 The performance of the

3 Wrap, Digestate & Compost in Agriculture, Bulletin 3 – March 2012 4 Large commercial digesters require a huge investment and therefore must operate over the 85% capacity in order to maximise gas production. 5 Small local AD networks could offer buffering capacity, i.e. it is more cost effective to relocate a £40K small digester if waste is reduced, than to decommission a £10m facility operating at 80% capacity and making a loss through reduced gate fees and tariff incentives. 6 AD is a microbial process and can be upset through long-term incorrect feedstock mix, lack of trace minerals, antibacterial contamination etc. A small-scale network would more easily absorb system downtime, with the network temporarily accommodating increased feedstock levels while maintenance is carried out. 7 Based upon the work of Batstone et al (2002) and Rosen et al (2006) with feedstock parameters from Bajzelj (2009)


controlled and uncontrolled (i.e. open loop) systems was compared under four biogas demand profiles. The control system advantages are summarised in Table 6 with full results in Appendix 3.

Table 6 - Performance of the controlled and uncontrolled systems

With control Without control

Protection against overloading when under a large biogas demand beyond the capability of the biological system to produce

Potential collapse and downtime of the system and difficult clean-up and restart in the event of overloading.

Feedback from biogas flow and biogas storage sensors used to control the biogas production which led to less excess biogas production

Unmonitored gas flow and storage may lead to the need to vent excess biogas more regularly.

Also, in comparison with expensive, bespoke PLC systems often used at large AD plants, hardware design based on „off the shelf‟ components commercially available in the consumer market, will allow rapid and low-cost development of custom systems for micro AD, with further cost reductions gained by replacing the modular design with a single PCB during in volume production. 4.3 Cost to industry/facilities including capex and opex It should be noted that the costs given in the Phase 2 budget are site specific and could be reduced further on a production basis, however, Table 7 outlines budget prices that are envisaged for various system elements.

Table 7 - System budget prices

Item Budget base price excluding VAT

Base Digester Systems

1m3 £1,324

2m3 £5,800

6m3 £12,000

20m3 £18,000

Ancillaries

Control systems Variable £1,270 to £2,700

Pre-feed system: mill, pump & 650l pre-digester £5,300

Pasteuriser - 1m3 £5,000

Biogas boiler £1,150

Water press separator Variable: £2,500-£3,500

Gas holders - .15m3 to 5m3 Variable: £200 -£3,500

Biomethane upgrading £2,500 - £30,000 (plus fill equipment)

4.4 Cost Benefit Analysis The figures below discuss those shown in Table 8 which are summarised from Appendix 5.


Using the model, all systems show a positive outcome; however, the 6m3 (Site 3) system shows a long payback, largely due to the overheads for the biomethane upgrading system. There are also increased operating costs due to biomethane upgrading and some infrastructure, which adds cost. If this cost is removed, the payback decreases to about 4 years. The calculations use actual Site 3 savings for disposing of existing waste. Site 4 currently take waste to an AD plant 70 miles away; their considerable savings of £185/week (£9,620/year) will be effected through savings in manpower, vehicle fuel, vehicle maintenance and gate fee reduction. Projects may be able to improve income by:

trying to add value to the digestate (which is given a fertiliser equivalent value in the illustration);

using the energy to attract the Renewable Heat Incentive and Feed in Tariff; and

the addition of some high energy feedstocks.

It is recognised that, on larger digesters, it can be challenging to obtain a good income from the sales of digestate, at least until the customers realise its value. In this model, an annualised depreciation (over 25 years) is added into the system cost, and repair levels have tried to take into account replacement values for certain parts or complete items of equipment. Any company that owns sustainable biofuel for use in road transport as it crosses the UK duty point8, regardless of its size9, is eligible to claim Renewable Transport Fuel Certificates (RTFCs), which may be traded to suppliers who are obligated to produce evidence that a certain percentage of their fuels come from renewable sources. The RTFC price is set by the market, so are variable, with a March 2013 auction price of 18p. The 6m3 (Site 3-Alara) digester would typically produce in the region of 2500kg biomethane and, assuming it can remain under the 2500kg threshold, be classified as an exempt producer. It would therefore be eligible for a net incentive of about 40 pence/kg biomethane produced. However, the 20m3 digester would produce much more than this, so would only be eligible for a net incentive of about 10 pence/kg. As a larger producer, the biomethane fuel data would need to be verified by an independent professional accountant, potentially incurring more cost to the project. The site economics in Table 8 below show the addition of the RTFC for these two sites, but does not include any potential professional fees which might be incurred for the largest digester as a non-exempt producer. It can be seen that, because of the lesser tariff and increased compliance costs, such digesters may wish to remain below the exemption limit, if other uses can be found for the biogas; however, this would have to be analysed on a case-by-case basis.

8 The excise duty point for biofuels is the time when they are (HMRC Notice 179E (August 2011)): • sent out from entered premises; • set aside; or • used as a motor fuel. 'Set aside' means the point at which it is decided that the product is going to be used as a motor fuel. This decision means that the fuel has been set aside for a chargeable use.

9 Size however has an influence on the dutiability of the biofuel produced. An exempt producer is defined as (HMRC Notice 179E (August 2011)): “If you have produced or used less than 2,500 litres of: • any biofuel, or • any other fuel substitute or additive within the last 12 months, and/or expect to produce or use less than 2,500 litres in the next 12 months, you are an exempt producer and do not need to register with us and account for duty.” 1 litre of biofuel is equivalent to 1 kg of biomethane.


Table 8 - Summary site economics

1m3 2m3 6m3 20m3

Feedstock

Feedstock (food waste) handled / day (kg) 20 40 120 400

Feedstock (food waste) handled / yr (kg) 7,300 14,600 43,800 146,000

COSTS

System Costs

Total capital cost 5,984 18,395 37,664 91,416

Annualised capital cost 239 736 1,507 3,657

Total operational costs (£/yr) 967 1,905 3,456 3,604

Total electrical cost - 282 1,287 4,228

TOTAL OPERATING COSTS (Waste handling, parts, digestate, maint, electricity)

967 2,187 4,743 7,832

TOTAL ANNUALISED COST 1,206 2,922 6,249 11,488

OFFSETS TO COSTS

Saved on disposal costs (£/yr): - - 3,000 9,620

Total recovered fertiliser value 33 66 196 652

Equivalent fuel cost (£) 3,044 5,730 5,326 17,752

Biomethane (RTFC) (£/yr) - - 1,000 860

Total Annualised Offsets 3,077 5,796 9,522 28,884

TOTAL NET INCOME (LOSS) 1,871 2,874 3,272 17,395

Simple Payback 3.2 6.4 11.5 5.3

4.5 Environmental cost benefit analysis Eunomia (2011) estimated that London creates approximately 13.5% of the England total of 7,973,887 tonnes of food waste per annum. Additionally, the overall strategic plan for London states that the city should manage its waste within its boundaries where practicable in order to improve the environment in a number of ways, including avoided waste transport. Policy in London also aims to supply 25% of its energy through renewable sources. WRAP estimates10 that every tonne of food waste reduced saves between 3.8 and 4.5 tonnes of CO2 equivalent. If this food were not wasted, the potential carbon reduction is shown in Table 9. However, even if just the CO2 emissions from removing these organics from landfill are taken into account, about 10%11 of these could be reduced, i.e. by digesting these organics, a potential 80.4 – 95.3 tonnes of CO2 equivalent could be reduced per annum.

10 Household Food and Drink Waste in the UK, Nov 2011 11 http://www.carbonindependent.org/sources_food.htm


Table 9 - Tonnes of CO2 equivalent emissions avoided

t/a 3.8 4.5

Site 1 7 28 33

Site 2 15 55 66

Site 3 44 166 197

Site 4 146 555 657

Total 212 804 953

Digesting wastes locally has a dual effect with regards to transport. The first is a reduction in food waste miles and the second is the replacement of petrol through the use of biomethane. Vehicles running on biomethane can reduce exhaust emissions of

12:

carbon monoxide (CO) by 70%;

non-methane organic gas (NMOG) by 87%;

nitrogen oxides (NOx) by 87%; and

carbon dioxide (CO2) by almost 20% below those of gasoline vehicles.

It can be seen from Table 10 that nearly 54 tonnes of CO2 equivalent13 could be reduced through replacing petrol with biomethane.

Table 10 - CO2e emissions (kg/yr) through biomethane use

Site 3 Site 4 Total

Litres of petrol 3,974 13,247 17,222

CO2e 12,459 41,531 53,990

With all sites treating a total of 211.7 tonnes of food waste per annum, the daily feed would be in the region of 578kg. Assuming a petrol vehicle doing 10km/litre (approximately 30 miles/gallon) has to do a weekly round trip to a digester/landfill 31 miles away, carbon savings of nearly 1.5 tonnes per year can be realised, plus savings about £636/year on petrol.14

12 http://www.ngvc.org/mktplace/fact.html 13 https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/3085/41.pdf 14 Based on a price of £1.45/litre

http://www.ngvc.org/mktplace/fact.html

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/3085/41.pdf


5.0 Legislation 5.1 Regulations and legislation applicable to the wider development and/or installation of

micro AD in the UK Two main sets of legislation apply when considering building food waste micro AD systems:

environmental permitting; and

Animal By-Products Regulations (under the AHVLA).

In addition, AD hosts collecting and transporting waste for a digester (unless produced on-site) are required to register with the Environment Agency as 'waste carriers‟. Community groups will need to register in the „lower tier‟. This is a one of registration and is free of charge, but failure to do so can lead to prosecution under the Waste (England and Wales) Regulations 2011. Alternatively, sites can receive feedstock from registered waste collectors. Finally, there are areas of the UK (Nitrate Vulnerable Zones – NVZs15) where nitrates must only be spread on the land at certain times of the year. The objective is to avoid such nutrients entering water courses in large quantities and is achieved by careful storage of waste until it can be safely applied to the land during dry periods. Such storage can be very expensive. 5.1.1 Environmental permitting AD is governed by:

Exemptions e.g. the T25 and U11.

Standard rules e.g. the SR2012 No 12, which allows food waste and a considerable range of other materials including up to 10 tonnes of farmyard manure throughput per day. See below for a list of wastes treatable under Standard Rule SR2010 No15.

Bespoke rules under the SI 2009 No. 3381 Environmental Permitting (England and Wales) (Amendment) (No.2) Regulations, Part 2 which contains the exemptions in detail and SI 2010 No 675 Environmental Permitting (England and Wales) Regulations.

5.1.2 Exemptions Exemptions due to scale and the low risk nature of activities recognise that small-scale/micro AD does not pose a threat to the environment, human health or the well-being of animal and plants. More than one exemption can be registered for as long as you are not having multiple permits of the same sort. Exemptions relevant to the proposed micro urban AD network sites include:

T25 – Anaerobic Digestion at premises not used for agriculture and burning of resultant biogas.

U11 – Spreading waste on non-agricultural land to confer benefit.

U10 –needed if some digestate was intended for agricultural use.

T25 summary

15

Nitrates Directive (Council Directive 91/676/EEC 0f 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources as amended by Regulations 1882/2003/EC and 1137/2008/EC) and the Nitrate Pollution Prevention Regulations 2008 (as amended by the Nitrate Pollution Prevention (Amendment) Regulations 2009).


allows biodegradable kitchen and canteen waste from municipal sources (EWC 200302) plus unsuitable for consumption and biodegradable wastes from markets to be used – see below;

total quantity waste on-site including materials in storage at any one time must not exceed 50m3;

minimum retention time 28 days;

the site must not be used for agriculture;

the gas has to be collected and burnt in an appliance to produce energy with a net rated thermal input of less than 0.4 megawatts; and

“associated prior treatment” means screening, chipping, shredding, cutting, pulverising or sorting waste for the purposes of anaerobic digestion.

Table 14 - Waste streams allowed under T25

Codes Waste types

020103 020107 170506 200201

Plant tissue waste

020106 Horse and farmyard manure only

200101 Paper and cardboard

200108 Biodegradable kitchen and canteen waste

020202 Animal tissue waste

020501 020601

Materials unsuitable for consumption or processing

200302 Biodegradable waste from markets only

U11 summary

Allows digestate produced by a T25 exempt Anaerobic Digester to be spread on non-agricultural land at a rate of 50 tonnes per hectare. You can also store up to 200 tonnes at any one time for a maximum of 12 months.

To provide, maintain or improve the soil‟s capacity as a growing medium by adding nutrients, or biomass”.

The waste is stored in a secure location prior to spreading.

At the time the spreading begins: - the land has not been frozen for 12 hours or more in the preceding 24 hours, and - the land is not waterlogged, frozen or snow-covered.

The location of any waste which is stored or land which is spread is at least 10 metres from a watercourse and 50 metres from a spring, well or borehole.

5.2 Registering exemptions The register that records exemptions will become public eventually. There is an online form but it is not easy to use. It is recommended that the electronic form be downloaded instead and posted or emailed to the EA. The link for the form is:


http://www.environment-agency.gov.uk/static/documents/Business/WEX001v02Aug10_e-form_Opt2_1.pdf 5.2.1 Animal By-Products Regulations The Animal By-Products Regulations (ABPR) are designed to protect animal and human health. AD systems are normally subject to the following:

animal by-products, including catering waste, must not be brought on to sites where farmed animals are present;

feedstock pasteurised for 1hr at 70 degrees Celsius;

maceration to 12 mm; and

digestate sent for testing to an accredited lab for indicator organisms (Salmonella and Enterobacteriaceae).

In future, if large micro AD networks are successfully realised, pasteurisation for all sites may be introduced using mobile hubs. However, all the AD plants for the proposed demonstration will be able to operate under the Low Risk Matrix Position (see below) and thus be exempt from the need to pasteurise feedstock. 5.2.2 ABPR exemption for small-scale community composting/digestion The recently introduced Home and small site composters and AD plants 'position‟ was developed by the AHVLA in association with AfOR, CCN and London Community Resource Network staff. It involves self-assessment using a risk matrix to determine if there is a requirement to register the operation with the AHVLA. Only where the activity scores too highly is registration a requirement:

Table 11 - Risk matrix and questionnaire

Question Yes No

1. Do you produce (or intend to produce) more than 10 tonnes of compost in a year?

10 0

2. Would the compost be used on: a) Horticultural Land or Parks b) Small holdings/ farms c) Domestic gardens or allotments

3: Horticultural or Parks 15: Smallholdings with animals/farms

0 Domestic gardens Allotments

3. Do farmed animals* have access to the area where the compost is made?

20 0

4. Do farmed animals* have access to the place where the compost is used?

15 0

5. Do more than 5 people have access to the area where the compost is made?**

3: Six to ten people 6: Eleven or more

0

6. Do you have (and follow) a biosecurity/ hygiene plan for your composting site?

0 4

7. Do you follow the AfoR or CCN guidance/ code of practice?

0 4

http://www.environment-agency.gov.uk/static/documents/Business/WEX001v02Aug10_e-form_Opt2_1.pdf

http://www.environment-agency.gov.uk/static/documents/Business/WEX001v02Aug10_e-form_Opt2_1.pdf


Total Score

If the score is 19 or over, you have to contact your local Animal Health and Veterinary Laboratory Agency (AHVLA) office and speak to the ABP officer. http://www.defra.gov.uk/ahvla-en/about-us/contact-us/field-services/ The proposal should be sent with a site plan (not necessarily to scale). Adopting the Community Composting Code of Practice achieves a lower score on the risk matrix. The link for risk matrix, questionnaire and guidance: http://www.defra.gov.uk/ahvla-en/disease-control/abp/compost-biogas-manure/home-small-site-composters-anaerobic-digestion-ad-plants/ Digestate distribution considerations Regarding the distribution of digestate produced under T25 and U11 exemptions, the EA are only concerned with the activities they cover rather than with product distribution methods. Therefore these exemptions would not pose a barrier to distributing or charging for digestate as long as the end users also have the relevant exemptions i.e. either a U10 for agricultural use or the U11 for non-agricultural use. However, when digestate is also produced under the ABP Low Risk Matrix position, the AHVLA requires that all end users will not be applying it to land accessible to farmed animals (these include pet pigs, pet sheep and domestic poultry). Charging a fee, even if only to cover distribution costs as a non-profit enterprise, moves the operation up the risk register as a commercial venture. It would then require application for full ABPR approval as what will be distributed is still technically classified as a waste. To proceed with digestate distribution beyond the host AD site without charging, all individuals /organisations planning to use it would need to be vetted and ideally have an agreement in place confirming that digestate would only be used on land not accessed by farmed animals. The implications for the project are that digestate could not be left for public collection, as is the case with some local authority produced compost, and all potential recipients would need to enter into a legally binding agreement as well as have a U10 or U11 exemption. Unless the agreements are worded otherwise, potentially, both distributing organisation and end user may be legally responsible for any breaches of use, despite agreements being in place.

http://www.defra.gov.uk/ahvla-en/about-us/contact-us/field-services/

http://www.defra.gov.uk/ahvla-en/disease-control/abp/compost-biogas-manure/home-small-site-composters-anaerobic-digestion-ad-plants/

http://www.defra.gov.uk/ahvla-en/disease-control/abp/compost-biogas-manure/home-small-site-composters-anaerobic-digestion-ad-plants/


6.0 Commercialisation of technology 6.1 The IP landscape From a patenting perspective, IP is relevant only to novel or inventive technology not already in the public domain. As such, all the components to be included in the proposed network are ineligible for protection, as they are either scaled versions of existing technology or exist in other sectors. Combinations of existing technology within the same field are not often patentable unless major barriers have been overcome and/or inventive steps have been taken. However, combining technologies across sectors resulting in an inventive step may be eligible. It is unlikely that patentable designs will result during this stage of the project; however, future commercialisation plans include two potentially patentable areas, detailed in 6.2. Even if applications are found to be unsuccessful, being able to use the phrase “patent pending” can be a useful commercial tool to attract investment and establish a lead and reputation in the marketplace. 6.1.1 The open source route The partnership is currently considering applying Creative Commons or open source licenses to the non-patentable AD system design and data outputs. They apply only to copyrightable material (images and text), so would in this case protect instruction manuals, assembly and installation guides and design drawings. The reasons for choosing an open source approach include the following:

the licenses are free and simple to apply for;

further optimisation and development of the technology can be managed as a collaborative, international, online open source design process, as successfully achieved by the GEK Project, describing itself as an experiment in collaborative science and open source engineering: http://www.gekgasifier.com

others are prevented from protecting the instructions and drawings, which would in turn prevent us using them in the future;

LEAP partners can still undertake to organise the manufacture and supply of systems but without monopoly; and

the technology can potentially be accessed by and benefit more people.

The main disadvantages of not having patent protection are that investors may be put off from funding something that a competitor could produce without the R&D costs. Losing control of one‟s IP could make it difficult to find a way to make revenue from the product. While a complete solution cannot be achieved as most of the technology is not patentable, the Non Commercial Creative Commons license version prohibits uses (of protected material) primarily intended for commercial advantage or profit, thus providing some legally enforceable protection against this scenario. This has the advantage of involving more people at the initial stages who can help publicise the project and technology as well as becoming a potential early adopters market. Although not strictly a form of protection, meeting CE mark requirements can act as a barrier for others wishing to copy equipment designs as substantial documentation must be submitted, which also serves as proof of due diligence should problems arise in the future.

http://www.gekgasifier.com/


Registered design protection will be sought once the visual appearance of the equipment is finalised. 6.1.2 Control system protection A different approach to protection will be taken with the control system as more options are available. Compared with open source products, proprietary software/hardware may initially look expensive, but using it ensures full control over IP and it becomes easier to develop business plans to generate revenue with the caveat that the selling price must be pitched correctly to ensure good sales and widespread uptake. The proposed data logger will be based on a proprietary solution from ioBridge Inc. with secure, encrypted links between the Server, gateway and the user‟s PC. The sensor links between the ioBridge gateway and the digester are secure within the local machine. The ioBridge Server provides public encryption keys so open source and third party software can gain controlled access to the ioBridge data feeds. Further details on each of the components involved are included in Appendix 3. 6.2 Overview of commercialisation plans The partnership aims to create the conditions to support the uptake of micro AD across a range of applications (heat, electricity, transport), and budgets (community to corporate). Strategic plans include:

demonstrating the versatility of micro AD by establishing a small network of cost-effective, efficient, robust systems, each featuring a different equipment configurations and biogas applications;

exploiting our Central London location to stimulate local and national media interest;

exploring educational opportunities as a means of publicising the technology, delivering open days and workshops for the local community, school and university groups, potential customers and industry partners;

managing an open source design process to continue optimisation of the technology, engaging international interest and input;

utilising the business plan and cost benefit analysis developed during this phase to attract further investment/funding;

developing several business models and system designs to cater for range of customers from low budget DIY community organisations and individuals to large corporate operations including hotels, hospitals, universities etc;

harnessing partner contacts to disseminate information about micro AD across corporate, public and community sectors and identifying new partnerships that may lead to wider deployment of the technology, e.g. with Waste Watch, 10:10, Local Authorities, property developers etc;

working through networks such as the Sustainable Restaurant Association and local Business Improvement Districts to publicise commercial opportunities; and

on-going market development to look at the feasibility of using digestate liquor year-round as an indoor plant food product, particularly for hydroponics and micro algae culture.

6.3 Market research

Several recent micro AD market research documents are briefly summarised in Table 12 below.


Table 12 - Market research summary

Source Findings Conclusions

The Gell Report (2008) Identified the cost of operation as the main economic constraint.

Potential shown through non-traditional economic assessment for uptake by communities whose goal is self-sufficiency.

With the emphasis on social and environmental benefits and the low return on investment, the third sector, with its not-for-profit ethos may be the most likely area for uptake.

Imperial College London Report (2011)

66,000 total potential UK customers.

8,100 potential customers in London.

6,400 properties whose cost of removal is high.

3000 properties with enough space.

2000 properties willing to install.

From the total potential customers for micro AD in the UK, 3% would be willing to install such a device in their establishment.

Of the 17% who already have organic waste collections, 86% would be willing to install micro AD if stated savings could were guaranteed.

Eco Comply market research (2012)

Digester demand would be stimulated by increasingly volatile oil and fertiliser prices.16

Estimated demand – one digester for every 10 people,17 extrapolated at 700 million units worldwide.18

The UK market was placed at over 1 million

While these figures are acknowledged as optimistic and that potential uptake will vary depending upon regional drivers, they are indicative of the potential size of the market.

16 Based on a number of data sources, including UN estimated gas demand at 31,000twh and fertiliser demand of 205.5 million tonnes (FAO 2011 official website). 17 Taking a lead from the Indian government calculations for micro AD, with 10 people roughly the size of an extended family. 18

Broken down as follows: China 130 million units, India 100 million units, Pakistan 15 million units, Bangladesh 20 million units, Rest of Asia 40 million units, Africa 300

million units, Latin America 50 million units, Rest of the world 25 million units, North America 20 million units.


units.19

TSB Future Cities Report (2012)

Twelve potential host sites were identified in 2 months including social housing flats, community centres and gardens, a transport depot, breweries, a city farm, food manufacturers, commercial properties, street markets and a school. Details are given in Appendix 3.

Interest in the technology is high as waste management costs and awareness of sustainability issues continue to rise. While a diverse market exists, with the technology able to serve multiple applications, urban siting needs extremely careful consideration, taking into account feedstock, fuel and fertiliser logistics as well as issues of odour, aesthetics, footprint and user friendliness.

19 Given the demand for replacing 1 million septic tanks and 5,000 to 100,000 new houses built each year. Demand from commercial food waste producers estimated at

60,000 units based on the number of hotels, restaurants, cafes, food production centres and supermarkets. Estimated demand for 40,000 units based on 10,000 farms and

10,000 sites to digest seaweed and marine waste (inland weed clearance) marinas, off-grid areas and hillside farming.


6.3.1 Export potential for micro AD

Utilising contacts in the international development and aid fields and profits from successful uptake of micro AD in UK/Europe, the project would seek to support deployment of the technology in developing countries where it is not yet established. Equipment costs would be minimised exporting flat-packed components in bulk and utilising local labour for assembly and installation.

20 With fewer sewage works and regulatory hurdles than advanced industrial

nations, developing countries are in a good position to reap multiple benefits. Micro AD could provide sustainable solutions to aid organisations establishing refugee camps in war torn countries or natural disaster zones,

21 and industrial, commercial, domestic or agricultural

sites where fuel costs prohibit biomass waste disposal by:

diverting sewage from local water systems to safeguard drinking water;

providing clean fuel for cooking & heating water (replacing wood and cow dung to reduce emission related health conditions) and electricity e.g. for vaccine refrigeration in hospitals or industrial/commercial use; and

Co-digesting animal, human and plant wastes to substantially reduce expensive, imported, artificial fertilisers (currently double the UK cost in some countries).

6.3.2 Competitors

There are a number of micro AD and composting competitors. Across the world, typical systems in this marketplace include: The Sino-Indian fixed domed systems, which require sufficiently skilled masons, steel and

cement. The Sino-Indian system is ubiquitous, but is sensitive to feedstock, local conditions and seasons and makes it unusable in winter in cooler climates.

Floating dome systems such as the ARTI Indian digester.

Gasification systems which require drying a woody feedstock and need a source of energy to start and maintain the operation. Gasification systems produce a liquid and the compost has a limited value. The construction of gasification systems requires high performance steels and cements, materials hard to come by in the developing world.

Bag digesters are also designed for simple construction, but are prone to puncture and temperature. It is difficult to put feedstock in or out. Bag digesters can be costly to maintain and need to be placed in a greenhouse for the best operational conditions. The same applies to plug flow units.

Digesters like those built in the UK by Methanogen UK, Muckbuster, Ch4e, React Environmental, SJS Biogas, Aardvark and SEAB.

Because CbD is an independent organisation, it can act as a centre of excellence and knowledge, aiding communities and individuals in project development through practical experience of micro AD. To this end, many of the companies above would not be competitors, but could act as suppliers for potential projects. 6.4 Sales projections Establishing digester sales projections at this stage of the demonstration is difficult because of the variability of the digester sizes and uncertainties around which sizes would be most

20 This approach, in manufacturing terms known as CKD or KD (complete knock-down or knock-down) avoids high shipping

costs and import duties associated with the supply of fully assembled units. In supporting new markets otherwise closed to low-

volume production, component costs can be lowered through increased batch sizes to offset tooling costs.

21 With currently more than 15 million refugees and 26 million internally displaced people (IDP‟s) in 52 countries around the

world, many overcrowded camps are becoming permanent homes, where people face rolling nutritional crises and outbreaks of diseases due in part, to insufficient sewage / drainage infrastructure and lack of food access.


cost-effective and practical for the UK market. However, the following table illustrates potential sales within the first three years and includes the support, consultancy, education and publishing elements identified above. Unit costs can vary depending upon infrastructure costs and gas use, but for illustrative purposes are based on the systems outlined in this project.

Table 17 - Illustrative sales projections

Item Unit Cost

Year 1 Volume

Year 1 Income

Year 2 Volume

Year 2 Income

Year 3 Volume

Year 3 Income

1m3 digester system*

£6,796

10 £67,960 30 £203,880 50 £339,800


£22,563 1 £22,563 12 £270,756 14 £315,882

6m3 digester system

£30,868 1 £30,868 12 £370,416 14 £432,152


£74,333 1 £74,333 14 £1,040,662 18 £1,337,994

Training Day Courses

£185 1 £185 4 £740 10 £1,850

Consultancy (days)

£250 20 £5000 40 £10,000 60 £15,000

Micro AD manual (ea)

£10 10 £100 50 £500 200 £2,000

TOTAL £201,009 £1,051,902 £2,444,678

6.5 Manufacturing plans

Although sales projections attempt to forecast a number of units to be sold per annum, production of hardware tends to be assembled in fixed size batches. Much of the production cost for a product is related to the time and effort required to set up the production line at the start of a batch and break it down again when the batch has been completed. For low volume production up to 100 units per batch, there are advantages to using and adapting off the shelf hardware as this can reduce development time and tooling costs. Since CbD works with suppliers of micro AD systems and ancillaries, manufacturing plans are largely in the realm of those separate businesses. However, CbD plans to work closely with these businesses in order that realistic delivery dates and suitable equipment specifications can be met.


7.0 Conclusion This report explored the feasibility of establishing a micro anaerobic digestion network in an urban environment. The network is designed to demonstrate a range of biogas applications including space heating and upgrading for fuel cell CHP and vehicle use, and includes remote monitoring and control capacity. The report has established that many of the elements present in a larger AD system can be scaled down for use in micro AD systems, but that the overall economics of using a particular piece of equipment depend upon a number of factors, including some site-specific elements, such as the ability to use the digestate and the cost of existing waste disposal. To this end, four micro AD system configurations have been proposed for Phase 2, each of varying size and sophistication in terms of pre-digestion, gas use and digestate handling. Data from the monitoring and control systems at each site will inform the evaluation of the demonstration and lead to further development of the technology and network opportunities.


Phase 2: Demonstrations

8.0 Objectives of the demonstrations The demonstration will mainly focus on the evaluation and comparison of the long-term economic, energy and technical performance of a range of digesters and peripheral components along with selected sensors including their reliability, accuracy, service and calibration requirements. Other specific aims during this period include:

determining optimum total solids content;

optimising biogas yield across all systems;

finding ways to reduce capital cost per m3 capacity to achieve targets informed by on-going market research, model the economics of cooperatively owned micro AD systems and attract investors for the technology;

optimising user friendliness and footprint and minimising odour for the urban context;

proving compliance of the technology with EA, AHVLA and Gas Safe/ATEX requirements, and establishing the legal and insurance implications;

development of a robust troubleshooting/emergency response system, to include software generated text messages and emails to alert operators in the event of malfunctions;

demonstrating digestate use and benefits to the public, ensuring it is utilised as locally as possible and expanding urban applications through trials involving hydroponics and Micro algae production;

sharing project learning online and through smart phone apps using software generated graphs and dials, engaging the public through open days and workshops;

minimising the environmental impact of the network;

working towards establishing the UK as a market leader in cold climate micro AD;

realising opportunities for data mining enabled by the monitoring system;

using data collected during the trials to optimise the control laws and/or update the control objectives to allow better management of the system; and

testing and optimising uptime of the data link and access to the cloud storage facilities.


9.0 Methodology for demonstration 9.1 Delivery of the demonstration Planning Site drawings (existing and proposed) have been produced for all participating sites. Plans will be reconfirmed or adjusted as necessary and full planning applications will be prepared and submitted. Meanwhile, suppliers will source and assemble the main components to the required specifications for each site. Once planning consents have been granted, ancillary equipment will be sourced, infrastructure construction will commence and insurance for the network will be secured. Site preparations Sites will organise dedicated operators who will receive CIWM accredited training. The training will be adjusted for the needs of each site and will incorporate commissioning, operational, risk management and decommissioning information gathered during this report period. Site agreements will inform operators of operating and monitoring requirements during the demonstration period– see Schedules 1-3 in the separate Site Agreement documents. CbD will liaise with sites on an on-going basis providing support where necessary, while maintenance and repairs will be carried out by the wider LEAP team. Network preparations Feedstock sources will be reconfirmed and arrangements appropriate for each site will be made for collections. Customers identified through digestate market research will be contacted and distribution arrangements confirmed. Assembly and commissioning periods will be staggered across sites (see project timescale below) so that each site can be attended to in turn. Once the main components have been installed, the pre-fabricated monitoring and control hardware system will be integrated, followed by a testing and commissioning phase, including siting and connection of the sensors. Gas Safe approval will be sought across the network once all the equipment is installed. Monitoring and communications Website development will take place alongside equipment installation to incorporate data feeds from the monitoring and control system, and updates covering project progress. Open days and publicity will be organised once systems are fully operational. The partnership will pool their list of contacts to publicise the project and disseminate learning as widely as possible. Continuous monitoring of the sites will be supported by laboratory analysis as outlined in the site agreements throughout the demonstration period, at the end of which, all sensor data will be evaluated along with the financial and socio-economic dynamics of the micro AD network. Results of this analysis will inform future developments and improvements to the design of equipment and the network service delivery model. Decommissioning In the event of the demonstration not evolving into a permanent scheme at the end of the period, decommissioning will take place involving de-piping and de-wiring the equipment for strip down and evaluation. However, all sites have an interest in continuing to operate the systems beyond the demonstration.


9.2 Key project milestones for Phase 2

Table 13 - Key project milestones for Phase 2

Milestone Date

Camley Street gas scrubbing installation 28/11/13

Calthorpe digester installation 04/12/13

Alara digester installation 17/01/14

Loop digester installation 28/03/14

Joint monitoring point 26/05/14


9.3 Project timescale

Figure 11 - Project timescale

A more detailed plan can be found on the separate project plan attachment.


9.4 Permitting & other approvals All network sites will operate under the T25 and U11 exemptions as the total volume of waste onsite at any one time will be under 50 tonnes and the retention time will be over 28 days. Applications for these exemptions can be made online and granted free from the EA taking five days to process. In addition, sites 1, 2 and 3 are eligible for the ABP Low Risk Matrix position. While most of the digestate produced will be used on-site, digestate that is distributed will be done so with agreements in place to ensure it is not spread where farmed animals are present. If Site 4 participates in the demonstration it will also be eligible for the T25 and U11. As it will be producing larger amounts of digestate and will need to distribute all of it on a commercial basis, pre-digestion at this site will involve pasteurisation and maceration in order to comply with ABP regulations. By time the demonstration phase begins, Community by Design will already be registered as licenced waste carriers to coordinate the collection and delivery of waste from external sources to the network sites. 9.5 Feedstock sources A number of feedstock sources have been identified to augment host sites‟ own supply. LEAP‟s 2012 food-waste survey with businesses local to the proposed network found 92% (of 25 businesses surveyed) were interested in diverting their waste to a local AD network. These sites will be contacted should the project move to the demonstration phase. The survey results can be seen in Appendix 2. In addition, three local food manufacturers/distributors have been contacted during this report period. Their descriptions have been included below as their participation in a successful micro AD project may have future implications across their chains and/or customers through positive feedback and publicity generated. Booker Group Booker‟s Development Director confirmed they “would want to support the initiative fully and look at ways to help our catering and retail customers do the same”. Booker is a FTSE 250 company and the UK's largest cash and carry operator, supplying approximately 338,000 catering businesses and over 83,000 independent retailers with 300 food depots listing over 18,000 lines of product including fresh and frozen food, beers, wines, spirits, tobacco and non-food items. Daily Fish Supplies Daily Fish always have an abundance of organic waste, which they currently send to Grimsby for processing, “and would be willing to divert an amount to the project.” They are a major supplier of fresh fish to the catering industry within the M25 area and operate from a BRC5 A-grade, EEC-approved depot employing 85 staff, with a turnover in excess of £16 million annually and are one of eight local depots serving customers throughout the UK.

IMS of Smithfield IMS would be “glad to divert some of our food waste to the project”. They generate bones, skin, tissue and out of date general meat. Their client list includes some of the biggest names in the catering industry. In 1988, they moved to a state of the art 7,500 square feet cutting facility. By 2000, the facility was at full capacity so the premises were expanded and re-modernised to house a 15,200 square feet high-grade facility.

http://www.brcglobalstandards.com/standards/food

http://www.brcglobalstandards.com/standards/food

http://www.directseafoods.co.uk/index.php/our-depots/


10.0 Cost breakdown

Table 14 - Cost breakdown

Micro AD Network – Indicative Phase 2 Budget – WRAP DIAD II

Item Cost (£) Cost in

kind (£)

Management and Admin

Project management

12000

Admin and management/indirect costs 23000 11000

Planning costs 1250

Insurance costs 2500

Site 1 - Installation - Calthorpe

0.5kW Solar PV + 2 x 110a battery + controller 1000

Digester - 1m3 1913

Gas Holder 200 litres, 3-7mbar & pipework, bell over water 500

Bladder 1.5m3 350

Biogas Boiler & installation 1650

Hot water tank (300l multi source) 2000

Monitoring: temperature, VFA, pH 3003

Settling tank 250

IBC digestate storage 150

Space heaters and pipework 340

Infrastructure including bunding, ventilation etc. 1000 1500

Low cost compression to small cylinders for heating 1500

Site 2 - Installation - Camley Street

Gas scrubbing upgrade 1500

CHP Stirling engine and installation 7500

CHP Fuel Cell 21000

Monitoring upgrade 2000

Site 3 - Installation - Alara

Digester 6m3 12350

Bladder storage 500

De-sulph & de-humidification eqpt 1880

Flame trap - approx DN10 size 50

Biomethane upgrading 7500

Gas compressor/filling unit 6500

5/10/15 gas cylinders incuding cage 2000

Small bottle storage - market trader cooking 200

Digestate water press 2500

Digestate storage - 4 x 1m3 IBCs 500

Digestate irrigation system 1500

Monitoring: temperature, VFA, pH 3223

Infrastructure including bunding, vents etc. 2000 5000

Greenhouse 3000

Biomethane vehicle 5000


Item Cost (£) Cost in

kind (£)

Site 4 - Loop

Pre-feed/pasteurisation equipment 8700

20m3 digester 18000

20m3 digestate storage 4000

Water press - digestate separation 3500

5m3 Gasholder 3500

De-sulph & de-humidification eqpt 1880

Flame trap - approx DN25 size 250

Biomethane upgrading 30000

Gas compressor/filling unit 6500

5/10/15 gas cylinders incuding cage 2000

Pipework + fittings + installation 2500

Infrastructure including bunding etc. 2500

Control and monitoring system 4233

Commissioning days 1&2 3000

Training 1500

Assembly etc

Sites 1, 2, 3 Commissioning Day 1 2400 1000

Sites 1, 2, 3 Commissioning Day 2 2400 1000

User Training per day 700 800

Site and O&M Documentation 1500 1500

Signage, touch screen monitors, vehicle graphics/design 3000

Gas regs/Gas Safe consultant 1500 500

Monitoring and evaluation

Monitoring and control system for Off Grid Gas network participation 2500

Monitoring and control system for Eco Comply network participation 2000

Ongoing monitoring and control system optimisation, data mining 2500 1000

Lab anaysis (feedstock and digestate) 3750

Additional elemental analysis 2250

Technical performance evaluation 2500 1000

Network costs

LEAP technical support 6000 6000

Travel and accommodation 2700

Website development 750

Continued digestate market development 1500

Electric bikes and trailers 2000

Educational activities, open days 1500

Operation and maintenance apprenticeships 12000 12000

Contingency (eg additional odour control, etc) 5000 2500

SUBTOTAL 142,292 186,130

VAT 28,458 37,226

TOTAL 170,750 223,356

Minus Camden match funding 198356

Minus Loop participation 115026


10.1 Project finance In the event of a successful WRAP DIAD II Phase 2 application, the demonstration would be funded through a combination of:

match funding - £25,000;

in-kind contributions - £115,026 (£198,356 with Loop involvement); and

funding requested from WRAP (£170,750).

Funding would be received through an account belonging to LEAP partner, Guy Blanch Bio Development Ltd. Match funding comes from the London Borough of Camden‟s Innovation and Development Fund, awarded to LEAP as part of a £100,000 grant over 2 years (2012-14) and allocated for the development of micro AD and related training and employment opportunities. All key partners will contribute in-kind contributions, in the form of labour and management time, as part of their commitment to the successful demonstration of micro AD. Host site partners are also committed to raising funds (detailed in site agreements) from commercial revenue, grant funding and/or CSR sources to cover some capital and running costs, and peripheral activities such as open days, digestate trials etc. Grant funding not yet secured, will be allocated to peripheral activities, thus not affecting core project delivery. Beyond the demonstration phase, the project will explore other avenues of investment such as crowd funding, which has proven successful for many emerging technologies. See the Kickstarter technology page: http://www.kickstarter.com/discover/categories/technology?ref=sidebar

http://www.kickstarter.com/discover/categories/technology?ref=sidebar


11.0 Evaluation and monitoring 11.1 Monitor during the demonstration phase The AD network will be subject to continuous online monitoring and laboratory analysis of:

feedstock composition;

digester and ambient temperatures;

gas production rate;

gas composition; and

digestate composition.

Informed by the data above, the following areas will be evaluated in order to understand their effects on biogas yield/quality, energy balance, process stability and digestate composition/quality:

automated vs. manual feeding;

pre-treatment of the feedstock;

co-digestion and feedstock variability and feeding frequency;

effect of heating the pre-digester;

seasonal/daily climate variability and ambient conditions;

use of greenhouse to house the digester;

optimisation of mixing regimes; and

recycling digestate liquor back to the pre-digester to dilute feedstock and wash down the mill.

To stimulate further system developments, additional areas will be monitored including:

required levels of operator support in maintaining the various components of the system e.g. sensor calibration, grit removal, manual monitoring etc;

levels of site owner, operator and local community engagement with the AD systems;

accessibility of data and ease of downloading data by: o the project team for analysis; o local digester operators; and o the general public.

the possibility of using electrical current measurements from the mixing motors as a proxy for total solid content (in the digester and pre-digester) will be investigated in order to optimise dilution levels;

the network‟s environmental impact including water, energy and fuel consumption as well as related emissions and CO2 savings; and

operator feedback, comments and suggestions to optimise user friendliness.


12.0 Key personnel, subcontractors and their roles Rokiah Yaman MA – Director of Communities by Design (CbD) Rokiah brings project design, management, communication and fundraising skills to her role as director of CbD, an organisation promoting greater community, economic and environmental sustainability. She led Camden‟s 2012 TSB Future Cities report and currently manages CbD‟s micro AD project LEAP with a particular interest in urban applications and enterprise opportunities. Her role in the team is project coordination, budget management, procurement, site liaison, planning and reporting.

Guy Blanch BEng (Hons) Research & Development Engineer A research engineer for Alvan Blanch (agricultural and waste handling equipment company) and other organisations, Guy is involved with export projects involving maceration and pasteurisation technology, a UK micro in-vessel composter project and has contributed to the Cwm Harry in the WRAP DIAD I report. Keen to encourage micro / small farm-scale AD biogas, particularly in Africa, he will be responsible for delivering the pre-feed, gas scrubbing and biomethane upgrading equipment for the demonstration phase. Methanogen UK Ltd – Anaerobic digestion supplier James Murcott graduated in mechanical engineering and co-founded Farmgas in 1975, developing the UK‟s first AD gas mixing system for sewage and farm based digesters and building the successful modular Farmgas „B‟ digester. He designed the popular, long-lived, plug and play WRI digester, the Fre-Energy digester de-gritting system and the Marches Biogas Agridigestore roof. His digesters have a combined operating time of over 400 years. He will be responsible for delivering the digesters and gas upgrading equipment.

Angie Bywater is a qualified project manager who has run a number of types of projects and authored several papers on AD, including the RASE report on farm digesters. She runs her own micro AD system. Angie will be responsible for systems integration and reporting. David Neylan - PhD, BEng, Environmental Engineering David has been involved with laboratory-scale AD research since 2002, gaining his PhD in Energy Crop AD at the University of Southampton. He spent several years conducting research to optimise the process biochemically and anticipate problems with long term stability of continuous systems. Recent work consulting with the Bridport Renewable Energy Group, involved investigating and implementing a micro AD demonstration project for small-scale food production and the development of a robust 1m3 system. Cath Kibbler – Coordinator - Community Composting Network (CCN) CCN have been working to introduce micro AD to its members and the wider community since 2004. In 2008, with WRAP/REalliance funding, they commissioned a two-stage micro AD report with a subsequent demonstration project including digestate trials in Newcastle. Cath developed micro AD policy and legislative channels including the Low Risk Matrix for Position with the Animal Health team at Defra and contributed to the WRAP DIAD I Cwm Harry report. She will evaluate the AfoR/CCN matrix assessment plan in action.

University of Leeds – System monitoring and control design Davide Poggio, MSc Chemical Engineering Davide is a PhD student at the University of Leeds currently working on the BURD (Bridging the Urban-Rural Divide) using a model-based approach to integrate AD with other renewable technologies for micro-grid applications in India. He was a technical advisor in Peru for 3 years, designing and installing rural micro AD systems utilising passive solar design, and a plastic tubular digester, which can be mass-produced for rural families in developing countries.


Mark Walker, PhD, MEng Mechanical Engineering Mark is a research fellow at the University of Leeds, also currently working on the BURD project. He has been researching AD since 2005, obtaining his PhD from the University of Southampton and publishing articles on a variety of AD-related topics. He has worked on several research projects developing a strong experimental background in lab-scale digester operation and monitoring with particular expertise in AD processes modelling. Mark and Davide will be responsible for evaluating the monitoring system data outputs and optimising the control system design across the demonstration network. Aleka Designs – Clive Andrews – BSc (Hons) Robotics, Control Systems and Mathematics Clive has over thirty years‟ experience with large corporations and small, specialised manufacturers. He established Aleka Designs Ltd to provide design and prototyping services with particular interest in electronic products than reduce carbon emissions and recycle waste. Recent projects include control systems for Evaporative Coolers and a water recycler for supermarket cleaning machines. Clive will work with the Leeds researchers producing the control system hardware and providing advice on moving from prototyping to full production.


13.0 Health, safety and risk

Table 15 - Phase 2 risk assessment

No Risk Impact

(1-10)

Probability

(1-10)

Mitigation strategies

Technology barriers

1 AD does not work to stated specification: Micro/small-scale AD is an emerging technology in the UK. Technical performance and business failure may occur.

I = 7-10

P = 3-6

A number of technologies from different suppliers have been included in the project, so the risk is spread and different technology suppliers have opportunities to perfect, adapt and modify their offerings at this scale in order to promote project-wide collaborative learning and minimise risk. The project would deliver training for equipment operators to ensure good practice, quality control and measure and look at optimisation strategies.

3 Lack of use for digestate: Disposal can be a problem for AD and potential users of digestate need to be made aware of its uses and benefits, i.e. market development for digestate.

I - 5-7

P = 4-6

Appropriately sized digesters will be sited where digestate can be used. Recent WRAP analysis would improve understanding and marketability of the product promoting its use locally. A large number of potential commercially interested stakeholders including green infrastructure developers, food growing networks, parks, community gardens, social horticultural projects, hydro- and aquaponics firms have been contacted with substantial interest recorded. The project would coordinate collection of surplus digestate from AD sites for local distribution.

4 Cost of CHP grid connection: one of the largest barriers for UK distributed electricity generation.

I = 3-4

P = .5-1

Micro-scale CHP minimises the necessity of upgrading existing infrastructure with the flexibility of being able to connect asynchronously on a single electrical phase. Should a CHP connection prove impossible for a particular site, proven micro-scale biomethane upgrading equipment would be used as an alternative application for the biogas.

Social/educational/cultural barriers

6 Lack of public support: A number of renewable energy projects have floundered due to public opposition, where concerns voiced about potential odour, vehicle movements, visual impact and other

I = 5-9

P = 1-4

Funding will be sought to deliver an exciting public engagement programme aiming to provide education around closed loop cycles and address specific concerns using an interactive platform and open workshops. The project seeks to involve local residents where possible in decision-making and a collaborative approach to urban future proofing.

Odour will be minimised through infrastructure design (double door system), hygiene protocols, the use of carbon filter ventilation and a 45 day feedstock retention period ensuring feedstock is fully


environmental problems.

digested. The not-for profit ESCO would be member run with strong local community links. The project would work with existing cross-sector networks to deliver its commercial and social advantages.

Most organic waste will be collected using bicycles and trailers and the aesthetic impact of AD plants will be managed by using attractive infrastructure where open to the public.

7 Resistance to Behavioural Change: particularly at collection stage and the use of digestate (covered in 3)

I - 2-8

P = 2-5

Incentives could be used to encourage „clean‟ collections, e.g. offering best-practice restaurants discounted food/flowers from local garden surplus schemes. Businesses would be offered waste audits helping reduce waste and showing how segregation can reduce residual waste disposal costs.

Financial and regulatory barriers

8 Planning permission, construction and commissioning cannot be achieved within project timescale.

I = 4-8

P = 4-5

Having already received an application for a pilot micro AD system, the local planning department are familiar with the concept of urban AD. Camden‟s planning department has an excellent track record delivering decision within set timescales.

9 The Regulatory Framework as managed by the LA, EA, AHVLA, and DEFRA

I = 7-8

P = 5-7

Engaging early with the EA and the AHVLA is crucially important. It has so far been established that:

Digesters can operate under a T25 exemption or a Standard Rule 15 depending on capacity.

Digestate can be used under a U11 exemption.

Systems can operate under the Low Risk Matrix Position created by the AHVLA and CCN.

10 The project is not self-sustaining and could not be replicated without the initial investment required by this proposal.

I = 9-10

P = 2-4

Business plans for micro AD networks and spin-off enterprises can be found in LEAP‟s TSB Future Cities Report. Other funding avenues will be explored including partnership bids with the LCRN for an ERDF food waste reduction programme.

Other urban areas wanting to replicate the same network with non-public funding/investment would benefit from FiTs and RHI. Beyond the mainstream commercial interests, the added-value of future-proofing needs to be holistically measured to gain valuable understanding on how this integration might be replicated.

13.1 Key H&S considerations See Appendix 6


Appendix 1 – Site information

1.1. Site suitability criteria The following criteria were used to assess the suitability of sites in hosting a micro AD system and to identify site-specific requirements and limitations: The sites:

main reason/s for hosting a digester;

current energy usage including seasonal fluctuations; and

available space including dimensions, existing layout and suitability, its current use, and other potential uses (to provide a cost benefit analysis if necessary).

Capacity of the site to:

provide feedstock, including details on type, amount, when produced/available, and proximity to the proposed digester location;

manage a local collection if required to augment their on-site feedstock supply;

utilise AD outputs including electricity, heat, refrigeration, biomethane, digestate (whole/liquor/fibre), taking seasonal variations into account;

operate an AD system;

store digestate for maturation;

storage to allow for variable feedstock supply and operational requirements (where single phase digestion is being considered); and

distribute digestate.

In addition, the following were assessed:

transportation distances of on-site feedstock to hub/digester, hub/off-site feedstock to digester and digestate to storage/processing/distribution;

current organic waste collection and disposal including collection frequency, segregation, Potential contaminants, gate fees and any contract issues;

any concerns about owning a digester;

site interest in financing own system for tariffs or need for external finance; and

any planned changes to site and energy/fertiliser use in future.

Planning considerations included:

conservation area locations;

flood risk;

proximity to sewers;

proximity to trees and root protection areas;

proximity to residential areas;

vehicle access; and

proximity to services (water, electricity, gas supplies).

The information gained from our survey enabled us to calculate the following for each site:

planning and equipment costs;

energy savings;

on-site feedstock mix and the need to augment the supply to minimise nutrient management and maximise outputs;

transport logistics and emissions per day/annum;

the need for caddies, bins and segregation education; and

potential waste management cost savings.


Where possible, additional details were gathered from the chosen sites including:

whether a site had single or three-phase electrics;

favoured timescale for construction and commissioning within the demonstration period;

existing site plans, tree surveys, contamination reports etc;

potential location/s for solar PV/thermal; and

site-specific requirements for access, construction, operation and maintenance.

For sites considering upgrading to biomethane for vehicle use, that following zoning issues apply:

the compressor has a 3m hazard area or Zone 2. Any electrical equipment within this area e.g digesters, gas scrubbing equipment etc. must meet Zone 2 requirements;

cylinder storage is also subject to a 3m Zone 2; and

the fuel dispenser i.e. post, nozzle and fill hose has a 20cm fill area so could be positioned either near the compressor or the cylinder storage.

1.2. Detailed site assessment summary The following table outlines the potential Phase 2 sites, the assessment findings and whether they were selected for the feasibility study.

Table 16 - Site assessment details

Site Assessment comments

Site Pros Cons/issues Decision

1. Alara Wholefoods

On-site food and green waste available plus good local links to secure additional feedstock and excellent capacity to distribute digestate. Able to utilise gas as biomethane in daily operations. Willing to underwrite food waste collection and part fund infrastructure costs.

Selected

2. Kentish Town City Farm

Good potential integration with educational activities, some feedstock on-site.

Difficult access to proposed site and infrastructure would need extensive groundworks and development to utilise AD outputs.

Rejected

3. Camden Transport Depot

Excellent opportunity to harness Camden‟s organic waste to supply existing biomethane refuelling station.

Capital costs too high for this proposal. Also, digestate distribution would require resources beyond available budget.

Rejected

4. Lithos Road Estate

On-site food and green waste potentially available. Potential to develop digestate and heat uses on-site.

Infrastructure costs may be too high for this proposal as currently no area suitable without modifications. Also, distance from selected sites makes it difficult to integrate.

Rejected


5. Camden Market

Large volumes food waste available on-site already segregated, big potential for waste management savings. Able to utilise all AD generated heat and electricity on site.

No capacity for digestate distribution without substantial support from the project, which would be unfeasible within the budget available.

Rejected

6. Maiden Lane Estate

Existing food waste collection involving residents and substantial food growing activity on-site, which could utilise some of the digestate produced and biogas for heat. Good proximity to the proposed network.

Management coordinating current food waste recycling initiative and in-vessel composter felt the site is not yet ready for a new technology.

Rejected

7. Kings Cross Central

High-profile mixed-use space which would utilise AD to manage organic waste from the entire site. Estate vehicles would be powered by biomethane and digestate would support food growing and greening on-site.

Capital costs too high for proposal and surplus digestate to require resources beyond available budget.

Rejected

8. Talacre Gardens

A neighbouring brewery could provide feedstock. Digestate would be used on-site to strengthen turf and plant growth and to support local food growing initiatives. Electricity used for park lighting, the rest along with heat, would supply adjacent sports centre.

Planning may be challenging, as site is a public park with Village Green status.

Rejected

9. Rhyl School

Good potential to utilise digestate with an extensive outdoor classroom featuring raised beds, a polytunnel and wormeries, plus a large roof suitable for food growing. Electricity and heat can be fully utilised on-site.

Planning may encounter difficulties due to location on school grounds and proximity to residential buildings.

Rejected

10. Calthorpe Project

Digestate can be utilised in established food growing area with greenhouse and polytunnels. Biogas generated heat can be used to support horticulture. Interested in managing local waste collection enterprise and distributing surplus digestate in the local community.

Proximity to residential buildings may cause planning concern so careful siting required.

Selected

11. The Roundhouse

Large volumes food waste produced on-site daily. Also, substation in close proximity to the potential AD site, from which heat could be captured to augment the AD process.

Lack of capacity to distribute digestate or utilise on-site.

Rejected

12. Hampstead Heath

Non-woody organic wastes from the parks and food waste from its 3 cafes would be included in the feedstock. Digestate would be utilised on amenity park areas. Electricity and heat utilised for site buildings.

Capital costs too high. Rejected



Currently hosting LEAP‟s first pilot micro AD system with a 2m3 digester. Additional components could be easily upgraded to demonstrate a wider commercial range of uses for biogas. Their network links enable distribution of digestate to local food growing groups. They can also utilise some digestate on-site.

Selected

14. Loop Recycling Ltd

Potential to divert the food waste they currently collect from a 60-mile journey for processing. Biogas can be utilised as either biomethane to fuel collection vehicles, or to generate heat and electricity for their commercial premises. They have capacity to locally distribute digestate produced.

May need project support to develop digestate market.

Selected


Appendix 2 – Market research tables

Table 17 - TSB Future Cities market research

Site PHASE 1 SITE DETAILS

1. Alara Wholefoods

Alara would combine their factory organic waste stream with locally collected food waste, They would utilise all AD products including digestate, CO2, electricity and heat for commercial greenhouses, growing tomatoes, a high nutrient crop, creating local training and employment in the process.

2. Kentish Town City Farm

Bringing currently disused contaminated land into use, the farm would employ digestate for land remediation1 enabling economically sustainable food production in greenhouses and development of an educational closed-loop community resource with cafe. Manure produced by farm animals would

augment locally collected food waste to balance trace minerals. Energy produced would supply the greenhouses and community space, with surplus directed to a neighbouring estate. Biogas would also be used for cooking.

3. Camden Transport

Depot

Existing Gasrec biomethane refuelling facility currently supplying 1 tonne biomethane p/w for Camden‟s own and several other local fleets. An AD plant would double capacity, supplying proposed fleet expansions (from 30 to 120). New AD infrastructure would house the extended biomethane fleet.

4. Lithos Road Estate

Housing Association estate, 180 flats with existing small orchard and a core group of residents keen to improve sustainability. Potential to expand food growing areas and develop micro enterprises producing food and collecting food waste, incentivising residents through reductions in energy costs.

Communications with UKPN have confirmed that waste heat could be captured from the neighbouring substation to minimise AD operating costs.

5. Camden Market

Large food waste volumes with 700 shops and 5 large restaurants with 700 seat capacities, some food waste currently segregated. Waste management costs between £10-20k p/a, an estimated 30% food waste. AD would help turn one of its biggest costs into an energy-generating asset.

6. Maiden Lane Estate

Council estate with active core of residents currently engaged in food growing and developing biodiversity corridor and forest garden on-site, AD would support expansion into mushroom growing, aquaponics and hydroponics, providing electricity, heat, fertiliser and CO2. Residents aim to establish a

weekly community market to generate economically sustainable enterprises, supporting residents through volunteering, training and employment. An estate with high levels of unemployment, this is particularly important for those on reduced benefits experiencing food poverty.

7. Kings Cross Central

The largest (67 acre) development site in Europe, Kings Cross is a mixed-use space which would utilise AD to manage organic waste from the entire site. As new tenants move in, it is an ideal time to implement waste management protocols diverting food waste from landfill. Businesses would benefit

from low collection costs. Estate vehicles would be powered by biomethane and digestate would support food growing and greening on-site.


8. Talacre Gardens

The only significant open space (2.4) acres for the 11,000 residents of Haverstock SOA. Some gas used for outdoor community cooking. Some electricity used for park lighting, the rest along with heat would supply adjacent sports centre. A nearby brewery would provide spent grain as

feedstock. Digestate would be used on-site to strengthen turf and plant growth and to support local food growing initiatives.

9. Rhyl School The school has an extensive outdoor classroom featuring raised beds, a polytunnel and wormeries. With a large roof suitable for food growing, they would expand their horticulture educational activities, utilising digestate to demonstrate a closed-loop system to pupils.

10. Calthorpe

Project

Community garden centre with kitchen and established food growing area keen to demonstrate closed-loop system. Interested in managing local waste

collection enterprise and operating own digester. Future plans include a new centre and café, expanding enterprise opportunities.

11. The Roundhouse

Has 2 cafes and is close to Camden Town and Chalk Farm, with large volumes food waste produced daily. They have their own on-site substation in close proximity to the potential AD site, from which heat could be captured to augment the AD process.

12. Hampstead Heath

The Corporation of London which manages the Heath would utilise AD to manage its non-woody organic wastes. Food waste from its 3 cafes would also be included in the feedstock. Digestate would be utilised on amenity park areas.


Table 18 - Imperial College report Question Posed Quantity

(N)

(%) Normalised result

(error margin = 1/((N)^0.5)

em = 16%

1. How many customers do you serve food to on a weekly basis? a. 0-50

b. 50-100 c. 100-300

d. 300+

40

0

6 13

21

0

15

34 50

0

0-31

18-50 34-66

2. How much waste do you generate on a weekly basis in the terms of bin bags? a. 0-10 b. 10-30

c. 30-80 d. 80+

40

0 3

19 18

0

8 48

44

0

0-24 32-64

18-60

3. Do you currently recycle? a. Yes b. No

40

8 32

20

80

4-36

64-96

4. How much do you currently pay for waste removal (£ per week)? a. 0-100

b. 100-200 c. 200-500

d. 500-2000

40 1

7 13

19

2 19

33 46

0-18 3-35

18-49 30-62

5. How much is your current gas bill, on a weekly basis (£)? a. 0-50 b. 50-100

c. 100-400

d. 400-1000

40

0 7

21

12

0

18 52

30

0

2-34 36-68

14-46

6. Would you be willing to install a device which converts waste food into gas that can be used for cooking? a. Yes b. No

c. Maybe

40 21

9 10

53 22

25

37-69 6-38

9-41

7. Would you be willing to separate organic waste from other waste? a. Yes, we already do

b. Yes c. No

40 10

21 9

25 53

22

9-41 38-69

6-38

8. Do you currently have enough space for a digester on your property? a. Yes

b. No

40 19

21

48 52

32-64 36-68

9. Do you currently have your food waste collected separately? a. Yes b. No

40

7 33

17 83

1-33 67-99

10. If you answered yes to 8; would you be willing to change in order to make direct savings to your gas bill? a. Yes b. No

7 6

1

86

14

em = 38% 48-100 0-52


Table 19 - LEAP 2012 food waste survey results


Interview comments MAP café „Recycling is a big concern to us. The Council has no system for commercial organic waste. Cost, of course is an issue, if separating organic waste reduced waste to landfill, the collection savings could cover food waste collection costs.

The Council only covers half of our recycling for £1200 a quarter; we have to do a second lot separately ourselves.

Camden Council Town Hall staff canteen „Food-waste collection needs to be budget neutral as we already spend £40 a week in waste collections. We have a roof garden, but it‟s underdeveloped. If developed to growing food we would be interested in bio-fertiliser (digestate).

Camden Stables Market „Waste collection costs are a major concern. I am very interested in anaerobic digestion to save waste collection costs, produce energy and support the use of carbon-neutral „green‟ energy. We currently have no man power or facility to separate the food waste from the other waste, and would like a service to help e.g. with food bins and daily collection times.‟

Kier Group „We are interested in recycling food waste to achieve better ratings in the sustainability of our operations. Reducing our waste to landfill would have a positive impact on the BREEAM outstanding rating for the completed building and help us reduce carbon from vehicle movements at site level; we want this to be part of our obligations to the Considerate Constructors Scheme in the „Good Neighbour‟ category and have a positive impact on our Corporate Responsibility targets and objectives.‟

InSpiral Restaurant „The council wouldn‟t collect our food waste so we contacted Veolia because we believe recycling is so important to our business.‟

The Lock Tavern „There's a big skip outside the pub where the bins are taken. We throw everything into a small bin in the kitchen. There‟s no space to recycle. I would love to grow some edible herbs in the terrace, but no there‟s no infrastructure in place.‟

Camden Town Brewery „Our food-waste is collected by a farmer outside London, who uses it to feed his pigs. We are interested in the potential of waste-to-energy and also to recycle waste locally if having our own digester isn‟t feasible.‟

Kings Cross HUB - social enterprise space, with café „Would local food waste recycling would mean we don't pay for collection or perhaps a reduced rate, as waste would be generating energy for someone? We already recycle food-waste and are very keen to recycle locally and be contributing to renewable energy production.‟

May Village café We don‟t recycle our food waste but we would love to. I contacted the authorities but they don‟t do it. We would certainly buy vegetables grown from food-waste fertiliser.

Karpo Restaurant ‘The owner financed a roof garden growing herbs, vegetables and fruit. It is not yet economically sustainable but we use some of the produce in our dishes. We are establishing slowly to see how it goes. We would welcome any support to maximise growing capacity in our roof-garden.‟

The Place - café located in an arts institution „We don‟t currently recycle food-waste, but have already saved waste management costs through recycling more (plastics and card) so keen to start. We are used to separating our waste to an extent so it should be easy to implement new system.‟


Appendix 3 – Control and monitoring

3.1 Control and monitoring system evaluation The main design challenge in the development of a control and monitoring system is the reduction of cost to allow feasibility of installation at micro AD sites. Traditionally, PLC (programmable logic control) systems, which are often used in large-scale AD systems, are delivered by companies offering a complete bespoke solution including hardware, programming, installation and commissioning, and the cost is very high. The type of sensors and hardware used in these large-scale AD installations cannot be transferred to small scale, due to the fixed costs involved. The design proposed here uses „off the shelf‟ components commercially available in the consumer market, which are designed to allow the rapid and low cost development of custom systems. An overview of the hardware design is shown in the auxiliary P&ID documents to this report. These show the structure of the control system, gives the main electronic hardware components, which will be used and their purpose within the system. The design is modular and scalable for the various prototype micro AD systems proposed in phase 2 in the ollowing ways:

The use of lock CuBloc relay8 allows an arbitrary number of analogue or digital inputs to be multiplexed to the main PLC meaning maximum flexibility of number of sensors and the sensor output types.

Both the internet and local user interfaces are available separately or together.

The control system is a standalone and optional extra executed on a separate Arduino Due microcontroller which uses a subset of the sensor inputs from the main monitoring system and can be deactivated if manual feeding is needed.

It is expected in larger production volumes that this modular „whole component‟ design would be replaced with the individual microcontrollers and required external electronics on a single PCB (printed circuit board) which would reduce the cost overall cost but at the expense of increased development time. The development of the design for the monitoring and control system has been broken down into the following stages which will be described in the subsequent sections;

Selection and description of the sensors.

Selection and description of the electronic hardware components.

Validation of sensor data.

The monitoring system and interface with the user and cloud.

Control system design and simulation.

3.2 Selection and description of the sensors In making the selection of the sensors for the monitoring system the primary criteria were to access the parameters which allow efficient and cost-effective monitoring of the process, to be able to withstand the potentially corrosive environment of an AD plant, to allow relatively uninterrupted operation and low maintenance. The parameters for effective monitoring of the biological process in AD could be selected from the following; biogas production, biogas composition, TS/VS, COD, alkalinity, pH, ammonia concentration, VFA concentration. Of these it is convenient to have online measurements for biogas production and composition and pH, since the other parameters require off-line analysis or expensive and/or cutting


edge sensing technology. Furthermore biogas quantity and quality allow evaluation of the economics and energy balance of the system. Further to monitoring the biological process, a number of other senses were selected to assess the non-biological parameters of the AD plant including the digester and ambient temperature, power consumption, volume of stored biogas. Finally alarm sensors for methane and hydrogen sulphide were selected to ensure safe conditions for operators and users of the AD site. 3.2.1 Gas flow Preference has been given to cost effective sensors, with adequate turndown ratio and resistance to corrosive gases (H2S). Pressure drop at the expected flow rates had to be negligible and less than the operating pressure of the digesters (20 mbar approx.). Thermal mass flow meters provide high accuracy, short response times and a wide flow range with no loss of accuracy at low flow rates. For that reason they will be installed where control is required, so to have fast and accurate measurement after the feeding events. Gas composition of the gas will be used to correct for eventual differences from the calibrated composition. Where only monitoring is require it would be of interest to test the operation of pulsed output domestic gas meters. These meters are available at much lower cost and could be used to provide a discontinuous estimate of biogas flow rate. The unknowns in this approach are the behaviour of these meters with highly humid and corrosive gasses. It is thought that with careful placement of moisture traps and/or the meter, condensation can be avoided. However the effect of corrosive gasses will be investigated as one of the outcomes of phase 2 since only anecdotal evidence supports the use of these meters in biogas applications. Flow measurements will be processed in the controller to take into account the influence of moisture content, pressure and temperature. Other gas flow measurement options, technically optimal, such as ultrasonic or wet drum-type, have been discarded for being not cost effective at this scale of operation. 3.2.2 Gas composition The control system simulations, presented in this report are based on a biogas production value; in this regard, the biogas composition sensor would be unnecessary for ensuring the process stability of the process. However, we have decided to include the biogas composition to ensure a better monitoring and accounting of the performance of the AD system. Biogas composition is an excellent indicator of process health and a reduction in the methane proportion can indicate a variety of problems with the sensitive methanogenic population within the digesters. In addition to this knowledge of the composition of biogas opens opportunities for further data processing which may be of interest to potential micro AD operators:

carbon accounting;

energy produced and/or energy balance; and

quality of biogas for optimizing biogas appliances.

Also, the proposed high-level (supervisory) control loop could be adapted considering the methane production instead of biogas production. It is proposed that during phase 2 this could be test following further simulation.


The proposed composition sensor has been selected given the materials resistance to H2S and the extensive calibration (from factory) which allows measuring CH4 and CO2 in the same instrument. Other solutions (solid state sensors) were deemed not adequate for constant CH4 exposure. Phase 2 monitoring will allow exploration of the possibility to measure only the CO2

concentration, and infer methane from a simple relationship. This would allow less costly measurement (only one CO2 infrared sensor would be enough). 3.2.3 pH

A differential type sensor has been selected, which uses three electrodes instead of the two used in conventional pH sensors. Process and reference electrodes measure the pH differentially with respect to a third ground electrode, allowing good accuracy, reduced reference junction potential, and elimination of sensor ground loops. By replacing the salt bridge and standard cell solution, these sensors can be regenerated for repeated use, allowing less downtime and maintenance. Exact lifecycle cost of the sensor would be not accurate at this stage, as it is dependent on the process conditions; however, it is expected a lifetime of at least two years given substitution of salt bridge and electrolyte every 6-12 months.

3.2.4 Current transducers

It is planned to use current transducers on the main electrical items on the AD plant to allow monitoring of the power consumption and therefore for real-time estimates of the energy balance of the plant. A further use of these sensors would be to detect faults with the electric mixing motors in the pre- and main digesters and associated pumps. Further to this it is hoped during phase 2 to investigate the ability to use the current drawn to the mixing motors as a proxy for the DM or TS content of the contained mixtures and allow a control target for liquor recirculation in the pre-digester. Knowledge of this correlation could allow better estimation of the organic loading rate and specific methane production of the digester, both of which are related to process health and performance and can be used to assess issues with the biological process.

3.3 Selection and description of the electronic hardware components

Off-the-shelf modules have been chosen for the Phase 2 stage of the project in order to reduce development time and simplify the design process. The PLC module provides a wide range of signal inputs and an easy route for expansion. The software for the module is tuned for data gathering and interfacing with external devices such as a panel, touchscreen or keypad. The internet interface provides a quick and easy route to accessing data on a cloud server.

3.4 Validation of sensor data

Effective monitoring and control of the process depends on the quality of the incoming data from the sensors. Some of the most frequent errors generated by sensors/analysers are missing data, measurement values out of range, peaks (outliers) and constant measurement values. Therefore, every time a new measurement is logged, the measurement is checked for these errors and the confidence in the value is calculated. When the confidence in the


measurement reach a minimum threshold, then the automatic control will be disabled to a safe default operation and an alarm will be triggered. Different methods are available for data validation. The following methods will be implemented in the proposed monitoring/control system. Details of the confidence functions for the various methods can be found in Olsson et al., (2005).

3.4.1 Missing data Every time a single data point is missing, the control action can be based on a default option or an estimate of the missing value can be used. Several possibilities exist for estimation of missing data (gap filling). In our case, we have selected the simplest approach of using the

value from the last measurement, which is appropriate and conservative for slow changing process as AD. Confidence decreases linearly for each consecutive value missing.

3.4.2 Values out of range

For every measured variable, it is possible to define a priori a range of values which are believed to be true. Measurement are validated when are within the working range. The defined range depends both on the sensor (full scale of the sensor) and the knowledge concerning the process monitored. The confidence in the data is set to zero when the value is out of range, and a “warning band” (with lower confidence) will be implemented for values approaching the accepted limits.

3.4.3 Rate of change check

A much higher measured value than the previous validated is usually caused by a disturbance in the sensor; it can be detected because the rate of change is much higher than the true variation in the measured variable. An accepted maximum variation (between two consecutive measurements) for each measured variables is defined a priori and based on that is possible to assign the confidence on the respective measurements.

3.4.4 Constant measurement value

A normally functioning sensor always has a small variation in its measurement value; while a constant value reported by a sensor indicates a failure or the necessity for cleaning. Therefore the confidence in the data decreases if the expected variation decrease and approach a zero confidence when the variation has nearly disappeared. The method is implemented using a running variance of a number of previous measurements. The minimum accepted variance is selected considering the measured variable and the characteristic of each sensor.

3.5 The Monitoring System and Interface with the User and Cloud

The monitoring system, in this case, refers to the processing and eventual transmission of the validated sensor data to the user and cloud interface. It is clear that the monitoring system will perform a number of functions ranging from; allowing full access to the system for authorised users to update control laws, to access raw sensor outputs, and change important parameters; to communicating important process information to public websites or mobile phone applications to allow users to remotely monitor their process. The use of the internet-cloud interface makes this possible.


The monitoring data falls into two main categories; those which come directly from sensor data, through an appropriate averaging operation and then fed to the user and internet interfaces. These include biogas flow rate, biogas composition, pH, current biogas storage level, digester temperature, ambient temperature, digester pressure, current pre-digester level (from load cells). The decision of the averaging period(s) for each sensed input will depend on a number of factors including; the nature of the physical quantity and its kinetics, the behaviour of the sensor (e.g. noise) and also whether a particular form is more informative or gives particular insight into the process e.g. biogas production in the last 24 hours, or biogas production this week.

The second category of data passed from the monitoring system is parameters derived from the either a single or multiple sensor outputs. These include the weight of waste added to the system, the process health, the energy balance, specific biogas/methane production, estimated organic loading rate. Again these values, once calculated, can be appropriately averaged to give useful information to the user e.g. weekly specific biogas rate may be an indicator of the general health of the process over that period. These values will be calculated using algorithms embedded in the CuBloc PLC. Examples for weight of waste added and weekly energy balance of are shown graphically in Figure 12. The digester health monitoring output is a qualitative state of the biological system based on the current and past sensor outputs. The algorithms used will be adapted from work by Murnleitner et al (2002) where fuzzy logic is used to detect the current state of the anaerobic digester and classify it into one of a number of categories including stagnant, shortage, acidifying pre-methanisation, overload etc.

Figure 12 - Example algorithms for derived quantities in monitoring system

(a) the calculation of weight of waste added to the add to the pre-digester

(b) calculation of process indicators; Organic Loading Rate and Specific Methane Production


Figure 13 - Selected sensors for the control and monitoring system

Variable Range Sensing

Principle Input

Output

signal

Operation &

Maintenance Notes Manufacturer Model

Cost £

(Excluding

VAT)

Methane

and

(Carbon

Dioxide)

Conc.

0-100%

(0-70%)

Non-Dispersive

Infrared (NDIR)

12 VDC

1.8W

RS232C

asynchronous

serial

4-20 mA

USB

Calibration: 2 yrs.

Maintenance: 2 yrs.

Cleaning of the

optical path and

eventual

substitution of light

source. Periodic

cleaning of filter in

sampling system.

Independent measure of

both CH4 and CO2 volume

fraction; internal

compensation for cross-

sensitivity.

Temperature and

pressure compensation.

H2S resistant.

*Pneumatic sampling

system included; with

water and particulate

removal system.

LumaSense

technologies

ANDROS

5111

666.00

*990.00

Carbon

Dioxide

Conc.

0-100% Non-Dispersive

Infrared (NDIR)

3-5 VDC 0.4-2V

Digital UART

format

Calibration: 1 yr.

Electronics embedded in

the sensor provides

linearized, temperature-

compensated output.

Output is set to 0V under

fault conditions.

Dynament TDS0054 120.00

H2S Conc. 0-10,000

ppm

Electrochemical

3 electrode cell

with potentiostat

Buffering

battery on-

board

0.2 to 2

mA/ppm

Sensor lifetime: 2

yr.

Drift: < 10 % yr-1

Discontinuous measuring.

Sensor housing, battery

and voltage protection

included.

Humidity range: 30-98%.

IT Dr. Gambert

Gmbh

I-42 202.00


Biogas

Flow

0.2–20 l

min-1

Thermal

dispersion (Mass

flow)

24 Vdc @

3.6W

4–20 mA

0 -5 V

Maintenance free.

Required: non

condensing gas

Omega FMA2812 496.00

0-6 m3 hr-1 Diaphragm -

positive

displacement

(Volumetric

flow)

N/A Pulse (every

cf)

Maintenance free.

Calibration : 1 yr.

Required: non

condensing gas

EK Metering PGM.75 77.95

pH 0 -14 Analogue

differential pH

sensor.

Glass Electrode.

Body material:

PEEK

- 0 - 0.8 V

Cleaning and

calibration: 1 month

Maintenance:

substitution salt

bridge and buffer

solution every 6-12

months.

Mounting: immersion into

tank.

Automatic temperature

compensation.

Built-in preamplifier.

To be connected to

STAMP before controller.

Hach Lange PD1P1.99 501.00

Temp. -20-70 C Thermistor

probe (10K)

Maintenance free. General purpose stainless

steel probe for air and

liquid

QTI QT06001C 20.00

Biogas

Storage

Level

0-2100 mm Draw-wire

displacement

sensor

14-27 VDC 4-20 mA Maintenance free.

IP54 protection class Micro-epsilon WPS-

2100-

MK77

187.00

60-2000

mm

Ultrasonic 10 -30 VDC 4-20 mA Maintenance free.

IP54 protection class Pepperl-Fuchs UB2000-

F42S-I-

V15

163.51

Digestate

Tank High

Level

Level Switch

Power to

electrical

motors

Primary

nominal

current:

5-50 A

Split-core

transducer

20-30 VDC 4-20mA

(RMS output)

Maintenance free.

- LEM AT-B420L 43.86


H2S in air 0-20 ppm Conductometric

- metal oxide

semiconductor

5 VDC N/A

Maintenance free.

Lifetime: 3-5 yrs.

Field calibration

available with Field

Calibrator and

Ampoules.

- General Monitors 50445-9 50.00

CH4 in air 500-10,000

ppm

Conductometric

- metal oxide

semiconductor

5 VDC N/A

Maintenance free.

- Figaro TGS 2611 30.00


3.6 Control system design and simulation A search of the literature reveals many different approaches to the control of anaerobic digestion systems of varying complexity. There is on-going debate about how best to control such a non-linear complex system using a limited set of on and off-line measurements but there is agreement that the control of AD is challenging due to the slow dynamics, the lack of actuators on the process and a lack of a reliable model of the process (Steyer et al. 2006). The situation for the control of micro AD is difficult since many of the approaches suggested in the literature require advanced sensors or off-line analysis which would be too costly. VFA is widely suggested as process indicator, and its accumulation in anaerobic digester is used as an indicator of imbalance in the process (Boe et al. 2010). However, VFA is usually measured off-line through laboratory analysis (titration or GC), and the effective detection of imbalance would require at least daily analysis (Kleyböcker et al. 2012). The cost and expertise that are required would be not cost effective at small scale. On-line detection of VFA is recently being experimented as well, improving the timely detection of imbalance. However the cost of these systems is still unviable for small scale; an example of this is the previous WRAP DIAD project investigating the use of MIR Spectroscopy for on-line VFA where the estimated cost of such a system is given as £40,000 (Murray et al. 2012). More appropriate to micro AD are the literature studies of a of controllers which use cheaper and more established sensors, for example the work of Scherer et al (2009) where only pH, gas production and composition are used in a fuzzy controller to successfully control the digestion of energy crops. The chosen control system is an adapted version of the „extremum-seeking‟ controller as described above (Liu et al. 2004). This controller was thought particularly suitable since it only requires the input of two sensors (pH and biogas production rate) and both protects the stability of the process while attempting to meet a particular demand in biogas production. The control system proposed by Liu et al (2004) includes a 2-level cascade controller with an overseeing supervisor. The cascade structure allows the controller to reject disturbances that appear in the influent such as a change in feeding composition. The purpose of the supervisor was to assess the state of the biological process and to increase, decrease or maintain the feeding rate in order to achieve the maximum possible biogas production. The flexibility of this control system is that the supervisor does not have to be used to maximise biogas production, as is shown in other research (Alferes et al. 2008; Alferes and Irizar 2010). In fact any control objective can be set by the supervisor while the cascade controller continues to protect the system stability. In our work we have developed a supervisor controller that adjusts the biogas production set-point based a combination of the expected demand from the biogas storage system and the quantity of biogas currently stored. The proposed controller allows the user of the AD system to „program‟ the digester to meet a particular varying biogas demand, which is envisaged will often be the case e.g. where the biogas demand during the weekday is much higher than at the weekend. The control system uses the single actuator of the feeding pump to meet the demand, where possible. 3.7 Simulation of the control system performance vs. „Business as usual‟

In order to test the performance of the selected control system, an existing model of an anaerobic digestion plant, created in Simulink, was modified. A graphical summary of the


model is shown in Figure 14. The digester was modelled as a CSTR using Anaerobic Digestion Model Number 1 (ADM1) (Batstone et al. 2002) using the Simulink model as described by Rosen et al (2006). Feedstock characteristics were taken from Bajzej (2009).

Figure 14 - Modelling scenario used to test the control system

Four expected biogas demand profiles were created; constant, moderate, challenging and extreme, shown in Figure 15. These were designed to having increasing difficulty for the management of the feeding regime of the digester. To increase the realism of the simulations and to test the adaptability of the control system uncertainty of +/ 50% were applied to both the feedstock composition and the actual biogas demand. The controlled AD system was compared with an „uncontrolled‟ or open loop system where the feeding rate was simply set proportional to the expected biogas demand for the following day, thus allowing comparison with a „business as usual‟ case. The controlled and uncontrolled systems were each subject to the four demand profiles totalling eight simulation scenarios. A summary of the important process parameters during the simulations is shown in Table 20.

Figure 15 - Demand profiles


In terms of the performance of the AD system when subjected to biogas demand profiles from constant to challenging there is little difference between the controlled and uncontrolled cases. The digestion process remained stable throughout the simulations and the biogas production, composition, pH and VFA concentration stayed well within acceptable ranges. The overall biogas production and waste fed to the digester over the simulation period (140 days) was similar meaning the specific biogas production remained mostly unchanged.

Table 20 - Summary of simulation results Controlled Uncontrolled

Biogas Demand

Profile Constant Moderate Challenging Extreme Constant Moderate Challenging Extreme

Biogas

Produced

(m3d

-1)

Av. 3.87 3.96 3.97 5.40 4.14 4.28 4.28 2.78

Max 7.05 7.14 7.86 8.67 6.91 6.93 7.94 10.22

Min 1.12 0.59 0.37 2.09 3.11 1.70 0.66 1.10

Biogas

production

(m3)

Total

(140

days)

551 563 565 769 590 609 609 389

Methane

(%)

Av. 54 54 54 53 53 53 54 1

Max 56 56 57 57 55 55 56 55

Min 50 50 50 51 51 51 51 0

pH Av. 7.10 7.09 7.09 6.99 7.08 7.07 7.07 3.94

Max 7.47 7.47 7.47 7.47 7.7 7.47 7.47 7.47

Min 7.04 7.03 7.02 6.95 7.05 7.03 7.00 3.76

Total VFA

(kg m-3

)

Av. 0.08 0.09 0.09 0.12 0.08 0.09 0.10 74.15

Max 0.21 0.21 0.29 0.33 0.18 0.18 0.28 104.35

Min 0.02 0.01 0.01 0.03 0.06 0.03 0.01 0.07

Number of

load events

Total 267 279 263 552 560 560 560 560

Waste fed

(kg)

Total

(140

days)

2351 2406 2418 3395 2528 2620 2621 5228

Specific

Biogas

Production

(m3 kg

-1)

av. 0.234 0.234 0.234 0.226 0.233 0.233 0.232 0.074

In terms of the performance of the AD system when subjected to biogas demand profiles from constant to challenging, there is little difference between the controlled and uncontrolled cases. The digestion process remained stable throughout the simulations and the biogas production, composition, pH and VFA concentration stayed well within acceptable ranges. The overall biogas production and waste fed to the digester over the simulation period (140 days) was similar meaning the specific biogas production remained mostly unchanged. However the case is different when the AD system was subjected to the extreme expected biogas demand profile. This represents an unfeasible demand from a 2 m3 digester at 7.28


m3 d-1. The uncontrolled system behaves as expected and the process quickly collapses, shown by the decrease in pH, biogas production and methane composition of the biogas. In reality after such a collapse the digester would require fresh inoculation in order to restart operation which would result in significant downtime. In contrast the controlled system does no collapse and instead continues to operate at high biogas production without inducing process instability. This can be seen in the pH, VFA and methane composition of the biogas results. The average biogas production of the system is less than the demand at 5.4 m3 d-1 and this demonstrates the behaviour of the „extremum‟ seeking controller which attempts to maximise biogas production whilst ensuring process stability. This represents the biggest advantage of the controlled vs. uncontrolled systems.

A further advantage of the controller can be seen in the ability of the AD system to meet the variable and unpredictable biogas demand. Figure 16 shows the excess and unmet biogas demand over the eight scenarios, represented as a percentage of the total biogas production. It can be seen that consistently the controlled scenarios result in reduced excess biogas production when compared with the uncontrolled system subject to the same biogas demand. However the unmet demand is higher in the controlled system in both moderate and challenging demand profiles which is due to the very slow response of the AD system to the actuator. It is expected that with further tuning using operational kinetic data that better performance could be achieved.

Figure 16 - Excess biogas production and unmet demand in all eight simulated scenarios

An example of the simulation data is shown in Figure 16 to further show how the control system adjusts to the biogas demand. The data shown is from the simulation of the controlled and uncontrolled systems with the challenging biogas demand profile. It can be seen that the controlled system responds to both the expected demand and current storage capacity to continuously set a biogas production set point to meet the current and future expected demand. In contrast the uncontrolled system simply follows a set pattern of loading and therefore is unable to adjust to the variability in demand.


Figure 17 - AD system behaviour example

(a) With control system

(b) Without control system

Example of the AD system behaviour with (a) and without (b) control system with the challenging biogas demand profile. Note there is no biogas production/storage set point in the uncontrolled system

References Alferes, J., J. L. García-Heras, I. Irizar, E. Roca and C. García (2008). "Integration of

equalisation tanks within control strategies for anaerobic reactors. Validation based on ADM1 simulations." Water Sci Technol 57(5): 747-752.

Alferes, J. and I. Irizar (2010). "Combination of extremum-seeking algorithms with effective hydraulic handling of equalization tanks to control anaerobic digesters." Water Sci Technol 61(11): 2825-2834.

Bajzelj, B. (2009). A comparative energy balance model of the anaerobic digestion of domestic food waste both with and without domestic sewage sludge. MSc, Imperial College London.

Batstone, D. J., J. Keller, I. Angelidaki, S. V. Kalyuzhnyi, S. G. Pavlostathis, A. Rozzi, W. T. M. Sanders, H. Siegrist and V. A. Vavilin (2002). "The IWA Anaerobic Digestion Model No 1 (ADM1)." Water Science and Technology 45(10): 65-73.

Boe, K., D. J. Batstone, J.-P. Steyer and I. Angelidaki (2010). "State indicators for monitoring the anaerobic digestion process." Water Research 44(20): 5973-5980.

Kleyböcker, A., M. Liebrich, W. Verstraete, M. Kraume and H. Würdemann (2012). "Early warning indicators for process failure due to organic overloading by rapeseed oil in one-stage continuously stirred tank reactor, sewage sludge and waste digesters." Bioresource Technology 123(0): 534-541.

Liu, J., G. Olsson and B. Mattiasson (2004). "Control of an anaerobic digester towards maximum biogas production." Water Sci Technol 50(11): 189-198.

Murnleitner, E., T. M. Becker and A. Delgado (2002). "State detection and control of overloads in the anaerobic wastewater treatment using fuzzy logic." Water Research 36(1): 201-211.

Murray, S., E. Groom and C. Wolf (2012). Use of MIR Spectroscopy for Optimisation of Biogas Plants. WRAP. Banbury, UK.

Olsson, G., M. Nielsen, Z. Yuan, A. Lynggaard-Jensen and J. Steyer (2005). "Instrumentation, Control and Automation in Wastewater Systems."

Rosen, C., D. Vrecko, K. V. Gernaey, M. N. Pons and U. Jeppsson (2006). "Implementing ADM1 for plant-wide benchmark simulations in Matlab/Simulink." Water Sci Technol 54(4): 11-19.


Scherer, P., K. Lehmann, O. Schmidt and B. Demirel (2009). "Application of a Fuzzy Logic

Control System for Continuous Anaerobic Digestion of Low Buffered, Acidic Energy Crops as Mono-Substrate." Biotechnol Bioeng 102(3): 736-748.

Steyer, J. P., O. Bernard, D. J. Batstone and I. Angelidaki (2006). "Lessons learnt from 15 years of ICA in anaerobic digesters." Water Science and Technology 53(4-5): 25-33.


Appendix 4 – Gas application and

scrubbing evaluations

4.1 CHP Units A review of micro CHP units for potential use with micro AD was made, with the two most promising contenders being the Baxi Ecogen (Stirling engine) and the Baxi Gamma Premio (PEM fuel cell). As the fuel cell CHP unit offers the most efficiency and the project may be eligible to trial a unit under EU funding, the information below was gathered.

The Gamma Premio (BGP) can utilise either low or high calorific gas. The following details were given by Baxi:

Table 21 - The Gamma Premio (BGP)

High calorific gas values Typical biomethane composition

O2 3 Mol-% CH4 96.15%

Max total S content (included odorant)

8 mg/m³ N2 0.75%

Sulphur limit for H2S and COS 5 mg/m³ CO2 2.9%

CO2 limit 2.5 Mol-% O2 0.2%

S1 < 3ppm

Electricity output is independent from heat output of the integrated auxiliary boiler, which has a modulating range from 3.4 kW up to 20.8 kW heat (depending on temperature of return flow). Electricity generation operating at optimum capacity could be in a range between 400 and 1000 W.

Depending on the lower heating value of the gas, the gas flow rate at 1Kw electricity production is approximately 3 kW gas input or 0.3m3 p/hr.

The gas flow rate cannot be fixed. However, a POWER OPERATED mode is possible, where the output is 1 kW electricity output. This mode is also limited by the heat demand.

Electricity to heat production is 1 kWe: 1.87kWth when the auxiliary boiler is not running (depending on return flow temperature). The unit cannot work without the auxiliary boiler, but heat production is dependent on heat demand.

As the unit works at 70 degree C, it is possible to turn it on and off without incurring long cool down/start up times, unlike solid oxide versions.


Table 22 - Specific requirements at the supply point on the H network

Unit Min Max

Gross calorific value kWh/m.(n) 10.28 12.81

Wobbe Index kWh/m.(n) 13.06 16.11

Pressure Barg xx.00 xx.00

Temperature °C Minus 10 38

Hydrogen sulphide content (H2S) (exclusive of COS) (as S)

mg/m.(n) - 5

Total sulphur at any time (as S) (1) mg/m.(n) - 150

Table 23 - Specific requirements at the supply point on the L network

Unit Min Max

Gross calorific value Kw/m3(n) 8.78 10.75

Wobbe Index kWh/m.(n) 11.86 13.03

Pressure Barg xx.00 xx.00

Temperature °C Minus 10 38

Hydrogen sulphide content (H2S) (exclusive of COS) (as S)

mg/m.(n) - 5

Total sulphur at any time (as S) (1) mg/m.(n) - 150

4.1.1 Long-term feasibility of fuel cell CHP units22

Numerous academic and industrial estimates place the cost of future mass-produced small stationary fuel cell systems at around $1,000 (£660) per kW, which compares well with targets set by agencies such as the US Department of Energy. Actual sale prices are currently 25–50 times higher even though mass production began three years ago.

Based on the findings of a systematic review of cost data from manufacturers in Europe, Asia and the US, along with near-term projections from manufacturers and other relevant organisations, a long-term target of $3,000–5,000 (£2000 - £3300) for 1–2 kW systems is more realistic, and could feasibly be attained by 2020 at the current rate of progress.

22 From The cost of domestic fuel cell micro-CHP systems, Imperial College London, (2012).


4.2 Investigating gas requirements for compression and combustion 4.2.1 Dew point limit If the area above in the graph below was shaded, CO2 in the shaded area would form a liquid at 0 degs C. Thus, at 35+ Bara and 100% CO2 the CO2 would turn to a liquid at a combined gas temperature of 0 degrees C as it would for values above all the other points.

Figure 18 - Dew point calculations

At 0 degrees C, the gas will remain gaseous at any pressure provided the concentration of CO2 in biomethane is less than 60%. A Lagrange curve fit was used to find a lower point, but it was unable to get the result down below 60% CO2. DEW pressures will be higher for higher gas temperatures and lower for lower gas temperatures and the compressor would run at elevated temperatures, which would push the DEW pressure even higher (moving it away from potential damage). However, there could be a problem in cold winter conditions at start up when both the compressor and gas are cold. In addition, where compressed gas is stored with high concentrations of CO2, liquid CO2 may form in the storage vessels if the temperature drops too low. This may or may not have safety implications. Allowing a margin of safety to take account of these provisos, a maximum CO2 loading in biomethane of around 40% may be acceptable, depending upon minimum design temperature for the storage.

4.2.2 Compression limits Taking the gas temperature down to -20oC, which would give a reasonable DEW margin for compression in the UK, the results shows that the limiting fraction of CO2 in biomethane for compression is a value below 40%. See graph below.


Figure 19 - DEW calculations at varying temperatures

However, compression characteristics of the gas for high-pressure storage are not the only factor that would limit the desired amount of CO2 in biomethane. A more critical percentage of CO2 would be required for stable combustion via commercial natural gas burners.

4.2.3 Combustion stability The combustion characteristics of the gas are more sensitive in respect to CO2 concentration. In plotting the Net Calorific value – the heating value of the gas when combusted, it can be seen from the graph below that the standard 50 MJ/scm falls away rapidly with greater concentrations of CO2 because there is less methane and an increasing amount of the heat is lost to heating CO2.

Figure 20 - Net calorific value (NCV) at varying CO2 percentages

More important than heat loss, is flame stability. To assess this, the gas Wobbe Nos. versus Weaver flame speed numbers graph was produced – see below.


Figure 21 - Flame Stability over Weaver speed factors

When gas is produced for combustion, an area exists within a Wobbe No. / Weaver No. diagram where stabile combustion occurs. Outside this area, combustion will have the following properties on commercial burners:

a. Not a practical gas for combustion - Weaver No. far too low. b. Incomplete combustion – Wobbe No. too high. c. Light back - Weaver No. too large. d. Lift Weaver No. too small.

It appears necessary to get the CO2 concentration below 10% to achieve a reliable gas for combustion. A stable flame is crucial to ensure that automatic burner control system work correctly and safely by ensuring that the combustion flame is guaranteed to be stable. The two points in green – below 10% CO2 satisfy the criterion. The remaining red points fall outside this criterion. Summary

To satisfy combustion requirement the CO2 level in biomethane should be less than 10%.

To satisfy high pressure compression, the CO2 levels should be less than 40% for ambient temperature no less than -10 digs C.

A water dew point of less than -25 digs C at normal ambient temperatures is required and lower still for severely low ambient temperatures. A commercial absorbent gas dryer will normally achieve a dew point of -40 digs C.

4.3 Gas scrubbing literature review summary by UCL collaborative programme For H2S removal, biological desulphurisation and iron chloride dosing have relatively low investment costs when compared with water scrubbing and carbon molecular sieves (Ryckebosch et al., 2011). Alternatively, the method of carbon molecular sieves can achieve up to 98% H2S removal, which is much more efficient than biological desulphurization and iron chloride dosing (IEA Bioenergy, 2010). As cost is the main selection criteria, technologies with lower capital costs have been chosen. Biological desulphurization (i.e. air injection into the digester) requires precise operation of an air injection pump, as overdosing of air can have a number of significantly detrimental effects on the process.


Iron chloride dosing was also a suitable candidate, as iron chloride can be directly fed into the digester slurry, with much less risk of impairing the AD process. Iron chloride removes H2S by the precipitation reaction forming FeS; equations are given below:

2Fe3+ + 3S2- → 2FeS + S

Fe2+ + S2- → FeS

However, this technology has a number of disadvantages. Its efficiency for H2S removal is low and Schomaker (2000) found that it can reduce the concentration of H2S in biogas to only 100 cm3/m3. Secondly, it has relatively high operational costs because iron chloride is expensive and has associated equipment costs of dosing pump, flow meter and isolation valve. This equipment would need regular calibration to ensure correct dosing. Thirdly, bio-chemical reactions within the digester may also affect the pH and temperature of digestion process, which may lead to a reduction in biogas production (Ryckebosch et al., 2011). Consequently, evaluation of iron chloride dosing has been suspended until funding permits further research. The UCL study recommended gas-liquid absorption membranes to remove CO2 in biogas. The operation of this technology is relatively cheap because the absorption membrane can work at atmospheric pressure (Ryckebosch et al., 2011). Figure 22 below is a schematic diagram of a typical membrane separation process, and it can be seen that the liquid absorbs the molecules from the gas stream.

Figure 22 - Diagram of membrane separation process (Source: Faure et al., 2012)

Apart from low investment and operational costs, this technology has the advantage of high efficiency in CO2 removal (Faure et al., 2012; Ryckebosch et al., 2011). Regarding the selection of the liquid, an amine solution is preferred, as it has been proven that the methane content of biogas can be upgraded from 55% to 96% in biogas by using the amine solution in this step (IEA Bioenergy, 2010). Nevertheless, this technology has two main drawbacks. Firstly, it is likely that methane losses happen throughout the entire process – approx. 10%. These losses might potentially be reduced by the utilization of recirculation, but there is a lack of sufficient experimental results data to prove this. Secondly, researchers have little operational experience in this area, which may bring unexpected problems during CO2 removal at the Camley Street Natural Park site (Ryckebosch et al., 2011).


Appendix 5 – Economic assessment

Indicative Business Case

1m3 2m3 6m3 20m3

Feedstock

Feedstock (food waste) handled / day (kg)

20 40 120 400

Feedstock (food waste) handled / yr (kg)

7,300 14,600 43,800 146,000

Costs

System costs

Control system

1,270 2,195 2,164 2,716

Pre-feed

- 5,300 - 8,700

Digester

1,324 6,150 12,350 18,600

Pasteuriser

- - - 5,000

Ancillaries

1,800 2,900 3,500 11,000

Gas use

340 1,350 17,150 42,150

Infrastructure

1,000 - 2,000 2,500

Commissioning

250 500 500 750

Total capital cost

5,984 18,395 37,664 91,416

Life of asset (years) 25 Annualised capital cost

239 736 1,507 3,657

Running costs

Standard Labour Charge (£/hr) 8.00 Operation (man-hours) (£/yr)

730 1,460 2,920 2,920

Parts

213 405 416 564

Maintenance (£/year)

24 40 120 120

Total operational costs (£/yr)

967 1,905 3,456 3,604

Electricity running cost

Electricity cost: £/kWh 0.10 Electricity use for digester heating - £/yr

- 105 394 175

Electricity use for digester mixing - £/yr

- 9 22 44

Electricity use for feedstock preparation - £/yr

- 168 - 1,106

Electricity use for separation

- - 38 126

Electricity use for biomethane upgrading

- - 833 2,777

Total electrical cost

- 282 1,287 4,228

TOTAL OPERATING COSTS (Waste handling, parts, digestate, Maint, electricity)

967 2,187 4,743 7,832

TOTAL ANNUALISED COST

1,206 2,922 6,249 11,488

Offsets to costs

Current waste handling and disposal costs

Gate fee (£/T) 15.00 - - - -

Savings on offset waste disposal

- - 3,000 9,620

Other

- - - -

Saved on disposal costs (£/yr):

- - 3,000 9,620


Digestate

Standard fertiliser value 4.46 33 66 196 652

Enhanced value-liquid (through marketing)

- - - -

Enhanced value-fibre

- - - -

Total recovered fertiliser value

33 66 196 652

Energy Biogas Produced (m3/yr)

1,003 2,006 6,019 20,064

Methane Produced (m3/yr)

602 1,204 3,611 12,038

Methane Produced (kWh/yr)

5,969 11,938 35,814 119,379

Energy savings (£/yr)

3,044 5,730 5,326 17,752

Biomethane (RTFC) Value (£/kg)

- - 0.40 0.10

Biomethane (RTFC) (£/yr)

- - 1,000 860

Equivalent fuel cost (£)

3,044 5,730 6,326 18,612

Total annualised offsets

3,077 5,796 9,522 28,884

TOTAL ANNUALNET INCOME (LOSS)

1,871 2,874 3,272 17,395

Simple Payback

3.2 6.4 11.5 5.3


Appendix 6 – HACCP

LEAP Urban micro AD network HAZARD ANALYSIS CRITICAL CONTROL POINT SHEET Location: Camden, London Compiled by: LEAP Date: May 13 Revision: VERIFICATION MONITORING CORRECTIVE ACTION RECORDS PROCESS STEP HAZARD CONTROL MEASURES CRITICAL LIMIT

CCP

Collections off

site:Collection of commercial

organic waste by company

staff

Product contaminated with

other materials not suitable

for anaerobic digestion [AD]

such as metal, plastic and glass which could

contaminate final product

• Instructions given to

business owners about what

wastes are acceptable in the

bins• Collection crews to inspect waste bins prior to

loading• Low levels of

contamination will be

removed by the crew during

collection or during on site

processing• Bins seen to

contain a high level of

contamination will be rejected

at the kerbside / customer’s

business premises• Staff

training on what is suitable for

the AD process• Readily accessible written / visual

guidelines on acceptable

levels of contamination for

businesses and collection

staff.

CCP1 Level of contamination to be

within an acceptable level

specified in site operating

procedures for domestic kerbside or trade catering

waste

Constant monitoring by

collection crew of bins as they

collect. Records will be kept

of dates and businesses with contaminated loads, to enable

monitoring and identification

of repeat offenders.

[1] Contaminated loads will

be identified and set aside and

GCC Land Services notified

to arrange collection. [2] Sticker placed on bin

indicating reasons for no

collection[3] Businesses

advised of permissible

contents of caddies, and if

contamination persists service

will be withdrawn.[4]

Periodic staff training on

waste segregation suggested

for businesses with high staff

turnover

Records kept of dates and

businesses with contaminated

loads, to enable monitoring

and identification of repeat offenders.

[1] Analysis of end product

for contaminants by approved

laboratory[2] Analysis results

reviewed by site manager[3] Visual inspection of delivered

product by processing staff

2. Delivery of organic waste

to Zone A - micro AD plant.

Kitchen residues delivered to

AD plant may be exposed to

vermin or birds.

• Catering wastes delivered in

purpose designed vehicles by

collection staff• Kitchen

residues are collected in

starch liners and transported

in 22 litre plastic caddies with

lockable lids. Even if the

buckets are knocked over the lids will not open. • Reception

of catering waste takes place

inside building with the doors

closed• The 22 litre plastic

caddies will be cleaned once

emptied and the bin storage

area will be cleaned after each

usage. Residues and

splashback will be processed

without undue delay.• Pest

control measures in place within facility – bait boxes

around the site and inside the

building• Driver to complete a

check sheet / defect report

weekly before leaving site

CCP2 Spillages either at the

collection point, en route or at

the AD site.

• All delivery vehicles will be

monitored by site staff and

any non compliance recorded

in the site diary.• Daily

records will be kept which

show the cleaning process has

been carried out.• Spillages

will be recorded

• Spillages will be cleared up.•

Site is not open to random

deliveries, only approved

customers who have been

made aware of site procedures

may drop off.• The cleaning

process is a specific

requirement of the job description. Failure to carry

out the task effectively will

result in disciplinary action.

• Spillages will be recorded.•

Daily records will be kept

which show the cleaning

process has been carried out.•

Details of all non-compliance

recorded in site diary along

with record of actions taken

All deliveries will be

monitored by site staff daily


CCP


3. Reception: Deliveries of organic waste from customers

Waste contaminated with other materials not suitable for AD

• Guidelines issued to customers who supply catering waste • Site staff to visually check load before acceptance • Low levels of contamination to be removed by site operatives• A load, which is heavily contaminated, will be rejected from site• Guidelines issued to staff for acceptable levels of contamination and training given to site operatives• Site operatives to visually inspect waste prior to processing

CCP3 Level of contamination to be within an acceptable level specified in site operating procedures for customer deliveries

Daily monitoring of catering waste by site staff and records kept in the site diary

• Loads which are heavily contaminated will not be put through the process• Non compliance report raised for repeat offenders• Waste will be rejected from site

• Details of all loads rejected will be recorded on site• Details of all non compliance recorded in site diary along with records of actions taken

• Analysis of end product for contaminants by approved laboratory• Analysis results reviewed by site manager• Visual inspection of end product on site reviewed daily by processing staff

4. Storage: Organic waste strorage at AD plants.

Kitchen residues may be exposed to vermin or birds.

• Organic waste produced onsite is stored in in plastic caddies with lockable lids or in vermin-proof sacks and transferred to digester within 48 hours. In the event of equipment failure for a period > 48 hours, waste removed to to a suitably licensed facility. • Reception of waste takes place inside a closed, vermin and bird proof building subject to pest control measures inside and out.• All organic waste delivered form off site sources will be processed upon delivery.• Housekeeping and hygiene procedures.• Preventative maintenance system to reduce processing equipment failure.• Repair and maintenance back up for processing equipment breakdown.• Process logs kept detailing deliveries and when material is processed.• Staff induction and training on procedures.

CCP4 Volume will be determined by digester daily feeding rate. If a backlog of more than 2 days' worth of feed exists, the oldest food must be disposed of to the suitably licensed facility.

• Traps will be checked daily for catch.• Daily monitoring of process logs for waste delivery and processing dates• Timetabled preventative maintenance schedule inspections and checks• Pest control inspections carried out by a contractor on a monthly basis• Daily site inspection carried out by site supervisor and findings recorded in site diary

• Non compliance notification raised in the event of failure of a critical control point.• Catering Waste will be sent off site if it cannot be processed within 48 hours.• Pest control measures increased if monitoring reveals a problem.• Retraining of site staff in procedure.• Disciplinary procedures for site staff in the event of repeat breaches.

• Records will be kept of the traps being checked, or of evidence of vermin.• Non-compliance details and actions taken recorded in site diary.

• Daily review of inspection reports by site supervisor• Weekly review of inspection reports by site manager• Contractual relationship with third party to satisfy CM 21 and to back up implementation of CCP 7 – emergency repair and maintenance


CCP 5. Routine hygiene: washing

down Zone A, storage and bin washing areas

Cross contamination of pre and post substrate through poor hygiene in Zone A.

• Prevention of cross contamination by compulsory PPE, designed site layout, and only authorised/trained personnel to work in the facility.• Inspection of Zone A before and after loading of Digester.• Preventative maintenance system to reduce processing equipment failure.• Repair and maintenance back up for processing equipment breakdown.

CCP5 • Daily site inspection carried out by site supervisor (including PPE and tools) and findings recorded in site diary.• Daily monitoring of process logs for waste delivery and processing dates.• Records kept to show cleaning has been completed in Zones A and B before and after loading the digester and the member of staff responsible.

• Non compliance notification raised in the event of failure of a critical control point• Retraining of site staff in procedure• Disciplinary procedures for site staff in the event of repeat breaches• Daily preventative maintenance schedule inspections and checks• The cleaning process must be undertaken on every collection/operation day.• Hygiene problems identified through inspections will be rectified immediately. Damaged, ineffective or contaminated PPE will be replaced immediately.

• Details of all non compliance recorded in site diary along with records of actions taken• The cleaning procedure frequency form will be filled in on every collection day. PPE will be inspected for "fit for purpose" records on a weekly basis. Personnel training records will be kept.

• Weekly review of inspection reports by site manager


Personnel will receive comprehensive training in hygiene, processing and monitoring steps.

Odour emissions and inhalation of bioaerosols

• Wastes delivered from off site sources will be processed upon arrival.• All onsite generated organic waste to be stored in either plastic lockable caddies or vermin/odour proof sacks for <48 hours.• Inspection of Zone A before and after loading of Digester.• Inspection of storage and bin washing areas after use.• Housekeeping and hygiene procedures - as soon as bins are unloaded, they will be cleaned. The storage and the bin washing areas will then be washed down immediately.• Preventative maintenance schedule in place and emergency repair and maintenance support available • Removal of stored catering waste to a suitably licensed facility in the event of equipment failure for a period > 48 hours.• Building closed during exposure of waste to air and vented, through bio-filter - negative air pressure maintained during operating times.

CCP6 Noticeable odour outside reception building.

• Daily site inspection carried out by site supervisor (including PPE and tools) and findings recorded in site diary.• Daily monitoring of process logs for waste delivery and processing dates.• Records kept to show cleaning has been completed in Zones A and B before and after loading the digester and the member of staff responsible..

• Non compliance notification raised in the event of failure of a critical control point• Waste will be sent off site if it cannot be processed within 48 hours• Retraining of site staff in procedure• Disciplinary procedures for site staff in the event of repeat breaches• Daily preventative maintenance schedule inspections and checks• Cleaning must be undertaken on every collection/operation day.• Hygiene problems identified through inspections will be rectified immediately. Damaged, ineffective or contaminated PPE will be replaced immediately. Personnel will receive comprehensive training in hygiene, processing and monitoring steps.

• Details of all non compliance recorded in site diary along with records of actions taken• The cleaning procedure frequency form will be filled in on every collection day. PPE will be inspected for "fit for purpose" records on a weekly basis. Personnel training records will be kept.

• Weekly review of inspection reports by site manager• Agreements in place with third party approved sites to take catering waste at short notice


CCP

Livestock having access to digestate after distribution

• All digestate to be contained within IBCs away with access restricted to site staff only.• Most sites will utilise digestate on site only for food growing/horticultural uses.• No despatch to agricultural pastoral uses.• Where digestate is distributed off site, legal agreements in place with all beneficiaries stating that digestate will not be used where farmed animals are present.

CCP5 Any contact between digestate and farmed animals

Records maintained on all digestate destinations.

• Re-training of distribution staff if any product found to have been used on an inappropriate site. Recall if possible.• Withholding further deliveries in the case of repeat breaches.

Waste Consignment Notes. 6. Use of Digestate

Resulting product contains residual pathogens

• All sites, including those under exemption not required to pasteurise their waste, will have routine digestate analyses carried out initially monthly, then quarterly after consistency has been proven.• Retention times and or pasteurisation settings may be adjusted accordingly.

CCP6 ABP approval criteria - salmonella absent in 25g; e.Coli within PAS110 approved limits.

Analytical records will be maintained for >2 years

Reprocess failing batch or dispose to suitably licensed facility

Analytical plus Waste Consignment Notes.

Review of analysis


7. Digester loading/feeding 1. Where a pre-feed system is fitted, ensure that the macerator cover is in place before the machine is operated. 2. On a system with direct hopper feed, ensure that the hopper lid is in place before the auger feed is activated.3. Where possible, ensure that the digester is in an enclosed building.4. Where a pasteuriser is included, loading takes place in a separate unclean area and cannot come into contact with pasteurised material.5. Spillages to be removed and cleaned in order to ensure area is clear of debris.6. Signs of vermin mean that action needs to be taken.

CCP7 No cross contamination of treated and untreated material

Log sheet for each feed of material is filled in.

In the event of cross contamination occuring in a system with a pasteuriser, the affected material will be processed through the system again.

Details of all non-conformances recorded in the site diary, along with records of actions taken.

Daily site inspections and final product analysis

8. Digester temperature Digester temperature is not within the specified limits, so feeding rate and retention time are affected.

CCP8 Digester tank is mesophilic and can operate at between 30 and 42 degrees C, but should be operating at between 38 and 42C.

Monitored through temperature probes and logged daily in site diary.

In the event of digester temperature falling, check the digester control temperature probes against the digester monitoring probes. If they are both the same and show temperature loss, heating source must be verified operational. If not the same, a probe is at fault and must be replaced.

Fault must be recorded in the site diary, along with records of actions taken.

Daily review by site supervisor; where fault is persistent, long-term corrective action must be taken.


CCP 9. Maceration/ Pasteurisation (where installed)

1. Potential for material not to be adequately pasteurised.2. Equipment breakdown

1. Temperature and time monitoring of pasteurisation.2. Feedstock is macerated to a maximum particle size of 12mm before pasteurisation.3. Preventative maintenance to reduce processing equipment failure, including regular control equipment maintenance4. Repair and maintenane backup for processing equipment breakdown5. Removal of stored catering waste to a suitable facility in the event of equipment failure for a period of >48 hours

CCP9 All waste must pass through maceration to <12mm and be pasteurised at 70C for 1 hour

Daily monitoring of process logs. Timetabled preventative maintenance schedule. Daily site inspection carried out by site supervisor, recorded in diary

Non-compliance notification raised in the event of failure of a critical control point. Material will be re-macerated and re-pasteurised within 48 hours or removed to suitable facility, depending upon nature of failure, ensuring site supervisor and site manager are informed of breach by email and upon inspection.

Details of non-compliance recorded in site diary along with records of actions taken.

Daily review of inspection reports by site supervisor. Weekly review of inspection reports by site manager.Agreements in place with third party approved sites to take such wastes at short notice.

10. Gas handling 1. Potential for harm to health2. Potential for explosion/fire3. Potential for negligent discharge to atmosphere.

1. Personal monitors must be worn when working in an enclosed spaces which could contain gas or in specified areas2. No smoking in zoned areas3. Operators to be trained on relevant equipment

CCP10 Within normal H&S specified limits

Through personal safety devices and those fitted to the equipment

1. Depending upon hazard, follow relevant health and safety guidelines for piece of equipment or limit breached

Details of non-compliance recorded in site diary along with records of actions taken.

Daily review of inspection reports by site supervisor. Weekly review of inspection reports by site manager.

Working document: for review

www.wrap.org.uk/diad

http://www.wrap.org.uk/diad

Documents

Optimising Urban Micro AD Networks