Communal Polyethylene Biogas Systems

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UPTEC F10031

Examensarbete 30 hpSeptember 2010

Communal Polyethylene Biogas

Systems

Experiences from on-farm research in rural

West Java

Isak Stoddard


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Teknisk- naturvetenskaplig fakultetUTH-enheten

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Abstract

Communal Polyethylene Biogas Systems - Experiencesfrom on-farm research in rural West Java

Isak Stoddard

In Lembang, a farming community onwestern Java, family-sized, plug-flow,polyethylene biogas systems fed with cowdung, are being used as an integratedsolution to issues related to energy,agriculture and waste management.Through simple, on-farm research andobservation, a number of key problemshave been addressed and improvementsmade to the design.

Due to the large supply of cow dung inthe area, and the potential to spread

the benefits of the technology beyondthe homes of dairy farmers, thefeasibility of developing a communal,polyethylene biogas system for severalhouseholds, has been investigated.Experiments on small model-digesterswere combined with observations of full-scale biogas systems in use. Measurementequipment and techniques wereconstructed and developed, in order tomeasure biogas production and otherrelevant process parameters. Resultsindicate that a communal system can bean appropriate choice, but only under acertain set of circumstances.

ISSN: 1401-5757, UPTEC F10031Examinator: Tomas Nybergmnesgranskare: Kjell Aleklett

Handledare: Sven Smrs


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Summary

Humanity faces a large number of global, interconnected and converging crises in both

natural and human-constructed systems. There is an urgent need for research that aims tounderstand their dynamics and find possible solutions to them. Local and contextualresearch is especially important in areas where the people will suffer the worstconsequences of the above mentioned crises. In the rural areas around the city ofLembang, on Western Java, people are experiencing an increased uncertainty in terms ofaccess to energy for cooking as well as other bare necessities. In the light of this situation,a local biogas initiative was initiated in 2007. Two years later, field work for this MasterThesis, contributed to the research activity of the initiative and helped to document thefindings of the past years.

Given the potential advantages and promises of communal solutions to problems ofregional resource scarcity, the main purpose of the study was to investigate the possibilityof developing a small-scale communal biogas system. Considering the economic situationof the local people, the systems were designed to be affordable and constructed out ofmaterials that are locally available (mainly polyethylene plastic and PVC-pipes). Thebiogas systems were analyzed both from a technical perspective, where different set-upswere used to conduct relevant experiments, and from a user perspective, where biogassystems in use were observed for a longer period of time.

Results indicate that it is fully possible to develop communal biogas systems but that theyonly should be constructed and installed given a certain set of circumstances. Regulationof gas flow, and a fair distribution of gas between connected households, turned out to bethe largest technical and operational challenge. The loading of the digester was alsoidentified as a major operational issue. In many cases a single-family system is a morereliable and wise choice.

There is a large potential for continued development and diffusion of biogas systems inthe area around Lembang. 10 % of the total energy demand for cooking could be coveredby small-scale biogas production, if all of the substrate from the many cows in the areawas used. Unfortunately, out of the 14 biogas systems that have been installed so far, amajority of them are no longer working as a result of either faulty design ormismanagement. This clearly highlights the need for further research as well astechnician training, if biogas is to become a reliable and important source of energy forcooking in Lembang.


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Table of Contents

1. Authors Note ........................................................................................................................ 42. Background ............................................................................................................................ 7

2.1 Setting the Context - Issues in Lembang ....................................................................... 72.2 The Biogas Initiative ..................................................................................................... 102.3 Purpose and Aim: Developing a Communal Biogas System ....................................... 122.4 Key Technical and Operational Issues ......................................................................... 14

3. Theory .................................................................................................................................. 193.1 The Process of Biogas Formation ................................................................................. 193.2 Biogas Production ......................................................................................................... 203.3 System Design ................................................................................................................ 28

4. Materials and Methods ........................................................................................................ 334.1 Experimental Set-ups .................................................................................................... 334.2 Measured Variables and Measuring Techniques ......................................................... 404.3 Biogas Systems in Use (Used for Observation and Evaluation) .................................. 48

5. Construction and Design: A Technical Perspective .......................................................... 515.1 Digester Dimension ....................................................................................................... 515.2 Slurry Flow .................................................................................................................... 535.3 Regulation of Gas Flow ................................................................................................. 575.4 Technically Feasible Biogas Production ...................................................................... 65

6. Installation, Operation and Maintenance: In the Eyes of The User ................................. 726.1 Available Space and Alternative Uses of The Land ..................................................... 726.2 Slurry Management ....................................................................................................... 766.3 Gas Flow Management .................................................................................................. 816.4 Balancing Biogas Production and Demand .................................................................. 85

7: Key Findings and Suggestions ............................................................................................ 957.1 Improving Single-Family Systems - Key Findings ...................................................... 957.2 Developing a Communal System .................................................................................. 977.3 When to Build a Communal System ............................................................................ 98

8. Biogas in Lembang ............................................................................................................ 1058.1 Potential for Diffusion of Biogas in Lembang ........................................................... 1058.2 Recent Development and a Look Ahead .................................................................... 110


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9. Conclusions ........................................................................................................................ 113Acknowledgements ............................................................................................................... 117Glossary .................................................................................................................................. 119References .............................................................................................................................. 125


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1. Authors Note

We live in a time of converging crisis - in both natural and human-constructed systems.Economic and social crisis are likely to increase in severity and frequency as we

experience the effects of the interlinked crises in ecological, climatic and energy systems.Most likely, we have already reached a peak in global oil production (Aleklett et al., 2010)and are quickly running out of other fossil fuels (Heinberg, 2007). Considering thecomplete dependence on fossil fuels in most agricultural and industrial processes, as wellas in the daily life and wellbeing of the majority of human beings, this is one of the mostcritical challenges of our time (and for our species throughout history).

Corresponding and parallel to the energy crisis, we are approaching a number ofinterlinked limits to growth: in human population, industrial output, food production,pollution and resource depletion (Meadows et al., 2004; Meadows et al., 1972). Buildingon this insight and the strong role of economic growth in driving us toward these limits, ithas been suggested that we are also approaching a limit to economic growth (Jackson,2009; Daly, 2010). Approaching limits (or tipping points), in a self-regulating system suchas the earth, has consequences. Climate change is just one (albeit very large) consequencewhich we are becoming more and more aware of but in many ways are completely failingto address (Hansen, 2009). Another way to approach climate change is to relate it to theconcept of interlinked planetary boundaries. Loss of biodiversity, ocean acidification anddisruption to the nitrogen cycle are other consequences of transgressing these boundaries,and which threaten the resilience of the biosphere and the stability of environmental

conditions that are conducive to human life. (Rockstrm et al., 2009)

The transition from a high-gain energy society (such as the one most humans live intoday) to a low-gain energy society1(such as the one we will most likely need to transitioninto) will require a paradigm shift of monumental proportion. Renewable energy such asbiogas, wind, geothermal, solar, wave and micro-hydro will obviously play a key role inthis transition. However, the fundamental differences of these energy sources (ascompared to fossil fuels) in terms of energy content, variability, energy return oninvestment, required infrastructure, distribution and effects on ecosystems, must be

considered. Otherwise, the renewable solutioncould end up creating new and largerproblems than it was trying to resolve (Tainter et al., 2003). Therefore, research intorenewable energy technologies, and how they affect and are affected by both natural andhuman-constructed systems, is of utmost importance in this day and age. As time isrunning short, a major push for renewable energy, such as is outlined in the recent UNreport A Global Green New Deal for climate, energy and development (UNDESA, 2009),is also of great importance. At the same time, local, traditional, indigenous knowledge as

1For definitions of high- and low gain societies, see Tainter, J. A., Allen, T. F. H., Little, A. & Hoekstra, T.W., 2003. Resource transitions and energy gain: contexts of organization. Conservation Ecology7(3): 4.


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well as local capabilities2must also be nurtured, and the advantages of bottom-updevelopment not be forgotten.

According to a national socio-economic survey in March 2007, there were more than 37

million people in Indonesia (around 17 % of the Indonesian population) living below thepoverty line (less than 2 USD of income per day) (BPS, 2007). Due to the serious problemsin food security, health and sanitation that may arise from insufficient access to energy forcooking, the Indonesian government has subsidized the price of kerosene since the 1970s.However, in the last few years, increased global oil-prices have stressed governmentexpenditure and led to heavily reduced subsidies on the price of kerosene. This hascreated large problems, mainly for the poor people of Indonesia, who have become utterlydependent on subsidized fuel for their cooking needs (Sulistyowati & Sutasurya 2008).

The poor peoples dependence on, and vulnerability to, an unstable global economy, could

be decreased by promoting small-scale, locally constructed, renewable energy technology.In order to be affordable to the intended users, and to be independent of external funding(from international or national funders, who in most cases also are more or less directlydependent on the global economy) the introduced technology must also be of low cost.Biogas systems are one of several promising renewable energy technologies which can fitthese criteria. Through rural development programs, mostly in the rural areas of centralJava, a few hundred biogas systems of various design and size have been built since theearly 1980s (Kossman & Pnitz 1999c). However, many of these systems have aconstruction and installation cost that is too high for poor people to afford. Biogas systems

made of cheap and readily available polyethylene plastic provide a possible solution to thisissue. However, there are a number of problems with these systems that are important toaddress (see section 3.3.3) - some of which have already been addressed by the biogasteam in Lembang (see section 3.3.4), the research documented in this paper (see section2.4) and some which require further attention (see section 8.2.2).

In the Background chapter of this paper, we will see that the situation of poor people inthe Indonesian rural setting is complex. The energy-situation is highly coupled with issuesof agriculture, sanitation, economic development, social stratification and environmentaldegradation. If implemented correctly, small-scale, polyethylene biogas systems could be acatalyst to the transition to a more resilient, localized and prosperous society. A key ideabehind the biogas initiative which this paper is a part of (see section 2.2) is thatcooperation and the strengthening of communal capital is a central part of such adevelopment. In the light of this, an investigation into the potential of developing acommunal polyethylene biogas system is at the core of this Masters thesis project. Themanagement of common pool resources (such as the sea, the air, the land and otherecosystems which we are directly dependent on) has within environmental discourseoften been seen as a case of the tragedy of the commons (Hardin, 1968). However, Elinor

2For a definition see, Sen, A., 1993. Capability and Well-Being. In A. Sen & M. Nussbaum, eds. The Qualityof Life. New York: Oxford University Press, pp. 30-54.


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Olstrom, political scientist and recent winner of the Nobel prize in economics,exemplifies and argues that this does not always have to be the case. Certain forms ofcooperation can lead to a successful management of local resources and resilient localecosystems (Olstrom, 1990). It is also in this spirit that this Masters thesis was carried out.

We will now take a closer look at the local context in which this project took place: therural community of Lembang, on Western Java.

Isak Stoddard

Uppsala, Maj 2010


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2. Background

The area of Lembang, and the many interconnected environmental, social and economical

issues that exist there, are introduced in section 2.1 below. A biogas initiative, that wasstarted in response to these issues, and the involved organisations are then presented insection 2.2. The Chapter then moves on to describe the purpose and aim of this paper insection 2.3. Lastly, key technical and operational issues for the development ofpolyethylene biogas systems in Lembang, are introduced in section 2.4. The structure andcontent of the main part of the paper (chapters 5, 6, and 7) is also laid out in the end ofchapter 2.4.

2.1 Sett ing th e Context - Issues in Lembang

What makes biogas an attractive option is the fact that this technology can provide

solutions to a variety of problems simultaneously. That is, if this variety of problems

exists.(Kossman & Pnitz 1999)

Bandung is one of the most densely populated areas in South Eastern Asia and also one ofthe worlds quickest growing urban areas. The larger metropolitan area of Bandung is

home to 7.4 million people. It is situated at approximately 800 meters above sea level, in abasin created when the ancient volcano known as Mount Sunda, erupted around 55,000

years ago. The crater rim is still lined with active volcanoes rising to a height of up to2,400 meters. Due to itsgeographic location and relative high altitude, Bandung and itssurrounding areas experience a rather temperate and cool climate, compared to the coastalcities of Jakarta and Surabaya. The rainy season extends from December to April andbrings cooler temperatures than the rest of the year (Lonely planet, 2007).

The area north of Bandung is a very important water catchment area. Besides providingwater for the city of Bandung, water falling in this area eventually meets up with theCitarum river, which flows all the way to Jakarta, providing water for drinking andagriculture (such as irrigation of rice fields) along the way. In this area north of Bandung,in the hills below the volcano of Tangkupan Perahu, lies the town of Lembang (see Figure2.1). Lembang is a bustling little market town with a large vegetable market and anincreasing amount of tourism. About 180,000 people inhabit the urban area of Lembang.Smaller rural communities are spread across the countryside around Lembang. The areahas experienced large economic growth in recent times, mainly driven by increasedtourism, vegetable farming and dairy farming. Vegetables and milk from Lembang are soldin Bandung as well as cities as far away as Jakarta and Bogor (Sulistyowati & Sutasurya2008).


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Figure 2.1: Map of West Java and a typical view over the Lembang area.

The large volcanic activity in the area around Lembang has resulted in very fertile soils.More than 83 % of the population in the rural areas around Lembang, are vegetablefarmers (22,000 people) and grow crops such as tomatoes, cabbage, chilis, cauliflower,corn, beans and many more. The agricultural practices are highly dependent on chemicalfertilizers and pesticides as well as manual labour (no tractors or animals are used). A manworking in the fields earns around Rp. 15,000 per day (1.5 USD)3while a woman will earnaround Rp. 10,000 (1 USD) (Sulistyowati & Sutasurya 2008). With this income they areconsidered to be below the poverty line (along with 37 million other Indonesians, or 17 %of the population) (BPS, 2007).

Dairy farming is the other major agricultural occupation in the area. According to KPSBU(a cooperative for dairy farmers in Lembang), there were more than 5,000 dairy farmers inthe area in 2006, together owning more than 12,000 cows and 3,000 calves (Cahyono,2009). A dairy farmer usually has between three and four cows. A few more prosperousdairy farmers may have more than ten. A dairy cow produces between 14 and 20 litres ofmilk per day and the price for a litre of milk is around Rp. 3,500 (0.35 USD). A calf costsRp. 3,000,000 (300 USD) and a full grown dairy cow Rp. 10,000,000 (1,000 USD)(Wahyudi, 2009). Average daily earnings for a dairy farmer are around Rp. 40,000 (4USD) (Sulistyowati & Sutasurya 2008), which is between three and four times more than avegetable farmer.

Due to very limited land availability and practical reasons, cows are stabled year round.The dung from the dairy cows is hardly ever used as a fertilizer. Dairy farmers seldomgrow vegetables and hence lack a direct incentive to use cow manure on the fields. Thequality of cow dung as a fertilizer is also perceived as low (as compared to chemicalfertilizers) and there are difficulties in handling and transport. Instead, the cow dung isplaced either in a pile next to the stables, until the rain flushes it away, or thrown directlyinto the river (see figure 2.2). The sanitary issues associated with this lack of waste

3All exchange rates retrieved fromwww.xe.comon 2009-12-20.
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the way that the technology is designed and diffused. If biogas systems are built and usedonly by dairy farmers, their economic situation will improve whereas the vegetablefarmers situation will stay the same or even worsen (being dependant on fossil fuels forboth cooking and inputs into their agricultural production).

With increased prices of cooking fuels and fossil-fuel based inputs in agriculture,vegetable farmers are experiencing an increasing economic stress. Less applied chemicalfertilizer, leads to lower yields which in turn leads to lower incomes. Besides being poorerand more vulnerable to global oil prices, vegetable farmers also lack the organisationalinfrastructure that the dairy farmers have (through the cooperative KPSBU).

2.2 The Biog as Init iat ive

In the light of the situation described above, an initiative to diffuse small-scale biogassystems in Lembang, was started in early 2007. The initiators knew that there was achance that a large-scale biogas plant would be constructed in the area. They felt that sucha solution may end up being more detrimental than helpful to the farmers in the long run,by locking them into yet another dependence on a system of which they had little controlover. Also, having witnessed and experienced the failure of a number of governmentfunded and NGO-run projects trying to diffuse green technology, the initiators felt therewas a need to investigate and better understand the dynamics of successful diffusion.Systems thinking and Innovation Diffusion Theory as developed by Rogers (2003) was

used to create a project plan and strategy that would be evaluated as the projectprogressed. The project is a collaboration consisting of four different organisations: YPBB,PESAT, KAIL and Change Agent Inc.

Yayasan Pengembangan Biosains & Bioteknologi (YPBB) is non-governmentalorganisation based in Bandung which focuses on environmental education and promotionof a more sustainable lifestyle. One of their main activities is to develop green

technology and find self-sustaining diffusion strategies for them. YPBB is the mainorganizer of the project. In the implementation of the biogas project they are in charge ofthe technical and environmental aspects. They are also in charge of developing andimproving the technology and the diffusion strategy through research and observation.

Foundation for the Development of Community Self Support (PESAT) is also a Bandung-based non-governmental organisation. PESAT involves rural communities in programs forclean-water provision and sanitation. Their approach is highly participatory and aims toimprove the communitiesoverall wellbeing and self-reliance. In the implementation ofthe biogas project, PESAT is in charge of the social and economic aspects of thetechnology. Prior to the introduction of the technology in a village (done by YPBB), theyhold several community meetings to listen and learn from the villagers about their

problems, and present biogas systems as a potential solution to some of them.


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Change Agent Inc. is a Japanese consultancy specializing in change and systems thinkingfor sustainability. They have provided a large amount of the financial resources needed forthe initial stages of the biogas project. They also have provided assistance on how to usesystems thinking and innovation diffusion theory for project planning.

Kuncup Padang Ilalang (KaiL) is a non-profit organisation specializing in increasingpersonal and organizational capacity for social transformation processes. In the biogasproject, KaiL acts as a supervisory organisation overseeing the project, assisting the projectteam in training, and coordinating with Change Agent Inc. of Japan. Lessons learned fromthe biogas project will be passed on to other projects and organisations that KaiL isworking with.

Besides these four organisations, a number of people from the village of Cicalung, wherethe first biogas system was installed, have been a crucial part in the development,

construction and installation of the biogas systems.

Between January and April of 2009, the project was really set into motion, and 15 biogassystems where constructed and installed in three different villages in the Lembang area.The villages were selected by using a number of criteria: there had to be a significantamount of cow farmers, they needed to be willing and interested in biogas, and finally, anumber of potential future biogas technicians needed to exist and be identified. Thevillages were also chosen because of their quite different social and economic dynamic,ranging from semi-urban (more competitively oriented) to rural (more cooperatively

oriented). This would hopefully lead to a better understanding of how diffusion andadoption of biogas technology works in different contexts, and the future strategies couldbe designed thereafter. For more information about these villages, and details about thebiogas systems installed, see section 4.3.

Prior to these installations, five biogas systems had been installed in the villages ofWangunharja and Cibodas in the years 2007 and 2008, a period of trying out variousconstruction methods and materials in order to improve the design. These improvementscan be read about in section 3.3.4.

These improvements were to a large extent a result of local research and observations.This research was continued and intensified in late 2008 in order to answer key questionsin regards to the construction and design of the biogas systems, before the biogas systemshave been widely diffused. This included research on: different ways to increase theprocess temperature, changing the dimension of the digester, increasing the stoveefficiency, the durability of the polyethylene plastic used for the bio-digester andconstruction of biogas lamps. This type of contextual research, which is performed inclose consultation with the users, has been called for in several studies evaluating thediffusion and impact of polyethylene biogas systems (An, 2002; An et al., 1997).


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The increasing economic stress on especially vegetable farmers in Lembang, described insection 2.1, lead the biogas project team to think about ways that the benefits of biogastechnology could be extended to include more than just dairy farmers. One promisingsolution, which also was hoped would lead to other advantages such as increased social

and economic equity, was to develop a communal biogas system that could be used byboth dairy farmers and vegetable farmers. The main objective of this thesis was toinvestigate the feasibility of developing such a system.

2.3 Purpose and Aim : Developing a Communal Biogas System

A great number of articles and papers have been written over the years saying that

community plants should be used in villages. They are more economic than individual

plants and could be of help for those people with too few livestock or too little space for

their own plant. The fact is that very few community plants have been built outside Chinaand, of those which have, only some are still working. Although there are some minor

technical difficulties, this is mainly due to sociological and managerial problems.(UnitedNations, 1984)

Considering the large amount of unused cow dung in Lembang area and the sanitaryissues associated with it, there is a need to find ways to increase the amount of dung beingprocessed and utilized. Most dairy farmers own more cows than are needed to produceinput for a biogas system of their own.The excess dung could be used to produce more

biogas and thereby spread the benefits of the technology beyond dairy farmers. This couldeither be done by building additional single-family systems or developing a communalsystem that can be used by several families at once. A communal system can be moreefficient in regards to the cost and space required for construction. Since there is a largeincome difference between dairy farmers and vegetable farmers (a factor of four), buildingcommunal systems will ensure that this gap will at least not grow any larger. Theincreased cooperation between the vegetable farmers and dairy farmers resulting from acommunal system, may also lead to a localisation of resource flows and economictransactions (e.g. fertilizer and milk is traded for vegetables). A common investment likethis may also help to increase the social capital between the families, if it is managed well.However, a communal system may also lead to problems and issues of operational,technical, economic and social nature.

Whether a biogas system is designed for one or several families, it should be efficient andadapted to the needs of the users as well as local conditions. In cooperation with the YPBBbiogas project team, a number of key operational and technical issues have been identified(see section 2.4) in order to ensure that the efficiency and appropriateness of the systemsare maximized. Therefore an underlying inquiry throughout this paper is to investigate:


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How can the construction and design of all polyethylene biogas systems including single-family systems) be improved in terms of their appropriateness and functionality in theIndonesian rural setting? (Research question 1)

Communal systems are here defined as a system that provides more than one householdwith biogas for cooking. They can be divided into two general types:

A system that is comprised of several connected (by gas- and/or slurry flow)digesters

A system that is comprised of one larger digester with gas pipes leading to thedifferent households.

Although communal systems have been designed and installed before, there has to datenot been any systems of the polyethylene-plastic digester type. This paper therefore aims

to answer the question:

Is it possible to develop a well functioning communal system with polyethylene plasticdigesters, with due consideration to key operational and technical issues of a biogassystem?(Research Question 2)In order to answer research question 2, the difficulties of developing a communal systemmust be identified and potential solutions investigated. Therefore a corollary researchquestion is:

What are the difficulties of developing a communal biogas system and how could they beovercome? (Research Question 2*)

Furthermore, if a functioning design of a communal system is found, the circumstanceswhen one should be constructed in favour of a single-family system, should beinvestigated. Therefore a third research questions is postulated:

Under which circumstances should a communal system be built instead of a single-familysystem? (Research Question 3)In order to answer research question 3, two corollary research questions were formulated:

What are the criteria and requirements when installing, operating and maintaining asingle family system, and what are they for a communal system? (Research Question 3*)

What are the potential advantages of installing communal systems and what are problemsthat could arise? (Research Question 3**)


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2.4 Key Techn ical and Operational Issues

In cooperation with the biogas project team, and in line with important considerationsmentioned in literature (United Nations, 1984), four key technical and operational issues

have been identified. These issues are all important to consider when developing acommunal biogas systems. Most of them are also crucial to the improvement of single-family systems.

Available Space and Alternative Uses of the LandAn appropriate design of a biogas system is dependent on the amount of land that isrequired for construction and installation. In many villages in the Lembang area there is ashortage of available land, and many competing uses of the land exist. The shape of theavailable land and its location in relation to the users and cow pen, also varies greatly.

Designs of biogas systems that may require less space per produced litre of biogas, or, bemore suitable to the space available, include communal systems and digesters of differentdimensions and orientation.

Slurry ManagementBy far the hardest and most time consuming task, in the operation of a biogas system, isthe transportation and handling of the slurry - both influent and effluent. How, and bywhom, this task is performed can have great implications for the functioning of thesystem. The location of the input and output in relation to the cow pen and households isalso important. For a communal system with several digesters, connecting them is of

interest since it simplifies the work of transporting slurry to and from the digesters.

Gas Flow ManagementA well managed distribution of gas flow is crucial for the functioning of a communalsystem. Each household connected to the system must be able to obtain a sufficientamount of biogas to fulfil their cooking needs throughout the day. A number of optionsfor regulating the gas flow exists and need to be investigated. The relative location ofhouseholds connected to a communal system, also has implications for gas flowmanagement and design. A difference in gas pipe lengths may lead to an uneven

distribution of gas flow due to different pressure drops in the pipes. The location ofpressure valves will also affect gas flow.

Balancing Biogas Production and DemandTo design biogas systems that are adapted to the needs of the users, biogas productionrates and the anticipated biogas demand need to be determined. An appropriate sizing ofthe digester is crucial in balancing production with consumption. The amount of cowdung and water available, the efficiency of the biogas production process and ways toincrease this efficiency should be taken into consideration. The consumption patterns offamilies also need to be studied. The quantification of these parameters helps to determine

how many cows, and what size of biogas system is needed to supply one or more familieswith sufficient amounts of biogas for cooking.


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An understanding of the social, economical and cultural aspects is highly important (notleast for communal systems) to get the systems to be operational and maintained correctly.These aspects are also much intertwined with the above technical and operational issues.

Due to this papers limited scope, we will not delve deeply into these issues. However,chapter 6 is based on observations from the villages of Pasir Angling and Cireyod, andhighlights some of the issues that can arise in the interface of the user and the technology,when the systems are being used. Chapter 8 also brings some clarity to the economicsituation of the farmers.

The technical and operational issues mentioned above are all tied to three importantstages of the biogas system development process: (1) construction and design, (2)Installation and (3) Operation and Maintenance. Chapter 5 deals with the technical issuesthat affect the construction and design of the biogas system. The methodology for this

chapter is mainly experiments and the data is quantitative. Chapter 6 deals withoperational issues and is based mostly on observation of systems in use and discussionswith users. The data for this chapter is mostly of qualitative nature. Chapter 7 ties the twopreceding chapters together by summarizing how it is possible to improve single familysystems, suggestions on how to develop communal systems and under whichcircumstances such a system should be built. Figure 2.3 provides an overview and outlineof chapters 5, 6, 7. Chapter 8 takes a look ahead at the potential to diffuse biogas systemsin Lembang and future needed research.

Figure 2.3: An overview and outline of chapters 5, 6 and 7.


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Each technical and operational issue includes a number of questions that are ofimportance to either single-family systems, communal systems or both. The followingfigures provide an overview of each issue, the questions belonging to each one and wherein chapters 5 and 6 they are presented.

Figure 2.4: Overview of the key technical and operational issue Available Space and Alternative Uses of theLand.

Figure 2.5: Overview of the key technical and operational issue Slurry Management.


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Figure 2.6: Overview of the key technical and operational issue Gas Flow Management.

Figure 2.7: Overview of the key technical and operational issue Balancing Biogas Production and Demand.

A high interdependence exists between several of the issues. Some overlap is thereforeimpossible to avoid. For example, the distance between the houses that are to beconnected to a communal system has implications for all four issues. Furthermore, therelationship between the issues is not immediately apparent. Therefore, a decision makingdiagram for developing communal biogas systems was constructed and can be seen inFigure 2.8. The diagram also serves as a conceptual framework for this thesis. The issue

Balancing biogas production and demand can be seen as one of the main goals whendeveloping a functional biogas system and is therefore placed at the bottom of the figure.However, many of the other boxes (e.g. Demand and Supply) are also directly connectedto this issue.


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Figure 2.8: Decision making diagram and conceptual framework for the development of a communal biogassystem. The four key issues can be identified more or less clearly. The boldest arrows symbolize the maincausal connections in developing a functional communal system. The medium bold arrows are necessaryfeedback mechanisms and the narrowest arrows are important factors affecting the final outcome.

The issue Available space and alternative uses of the land canbe found in several placesin Figure 2.8. Slurry management and gas flow management come in as important factorsaffecting the final goal (which is to balance the biogas production from all digesters withthe biogas demand of all households). That iterative character of the process is symbolizedby the many feedbacks (the medium bold arrows in Figure 2.8).


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3. Theory

The very long history of biogas formation and the three main stages that it involves aredescribed in section 3.1. Biogas formation here refers to the natural microbiological

process. Biogas production, on the contrary, refers the controlled digestion of organicmaterial to fulfil human needs (such as producing biogas for fuel and treating organicwaste). The history of biogas production and key physical and environmental processparameters are introduced in section 3.2. In section 3.3, the design of biogas systems areexplained and discussed. The focus is on the system design used in the Lembang area, itsshortcomings, and the improvements that the biogas project team has made to this designin the last few years.

3.1 The Process of B iogas Form ation

3.1.1 History

Methane producing bacteria, also known as methanogens, are some of the oldest life formson earth. Several billion years ago, long before cyanobacteria evolved and created anoxygen rich atmosphere by inventing photosynthesis, methanogens dominated life onearth. Today methanogens are found in the anaerobic environments that still remain from deposits deep in the earths crust (where they convert plant-material to oil andnatural gas) to the bowels of herbivores (where they are an essential component in the

digestion process). (Nrretranders, 1994)

3.1.2 The Three Stages of Biogas Formation

Biogas is a product of a microbiological process, known as anaerobic digestion, in whichorganic material is decomposed in an anaerobic environment (Ek, 2007). Methanogens are

just one of the micro-organisms involved in this process. Fermentative and acetogenicbacteria also play a key role in the process, by splitting organic material and providing afavourable environment for the methanogens. There are essentially three stages to biogasformation: hydrolysis, acidification and methanogenesis (see Figure 3.1).


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Figure 3.1: The three stages of biogas formation: hydrolosis (Stage I), acidification (Stage II) andmethanogenesis (Stage III) (Kossman & Pnitz 1999a).

In the first stage (hydrolysis), fermentative bacteria decompose the long, complex chainsof carbohydrates, protein and fats into shorter chains. E.g. proteins are split into peptidesand amino acids, polysaccharides are converted to monosaccharides. In the followingstage (acidification), acetogenic bacteria converts the intermediates of fermentativebacteria into acetic acid, hydrogen and carbon dioxide. They require carbon and oxygenfor this process, effectively removing oxygen from the process and creating the anaerobicenvironment that is essential for methanogens. In the third stage (methanogenesis),methanogens use the newly produced compounds of low molecular weight, such as acetic

acid, hydrogen and carbon dioxide, to form biogas. (Kossman & Pnitz 1999a) Biogas is amixture of essentially methane and carbon dioxide. However, traces of hydrogen sulphide,ammonia and oxygen in the biogas may also be found at times (Gustavsson, 2000).

3.2 Biog as Product io n

The biogas formation process can under controlled circumstances provide humans with avaluable source of energy. In contrast to aerobic digestion processes (such as composting),anaerobic digestion is characterised by small heat emissions (Gustavsson, 2000). Much of

the energy stored in the biomass is transferred to the methane and released whencombusted. Consequently, anaerobic digestion is very suitable for the extraction ofenergy.

3.2.1 History of Biogas Production

The burning behaviour of biogas was first investigated in the 1770s by the Italianphysicist Allesandro Volta. More than a century later, the French chemist andmicrobiologist Louis Pasteur conducted research on biogas from animal residues and

proposed that horse dung should be used to produce biogas for street lighting (Kossman &Pnitz 1999a). Today, biogas is used extensively throughout the world as a source of


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renewable energy. In more industrialized countries, large scale biogas facilities are used toprocess organic waste as well as produce transport fuel and electricity, in both rural andurban areas. In less industrialized parts of the world, biogas is used mainly for cooking andlighting, and especially in rural areas. Two countries stand out in this regard: China and

India. By vigorous promotion and extensive support from the government, severalmillion family-sized biogas systems have been installed in these countries in the last fewdecades (Kossman & pnitz 1999a). However, many of these systems have ceased tofunction shortly after installation, due to limited knowledge of operation andmaintenance routines (An, 2002).

3.2.2 Key Physical and Environmental Process Parameters

The process of anaerobic digestion can be monitored and evaluated by looking at anumber of physical and environmental process parameters. They can be divided into

parameters that affect the magnitude of the biogas production (see section 3.2.2.1), andones that do not but still are important (see section 3.2.2.2).

3.2.2.1 Parameters Affecting Biogas ProductionThe physical and environmental parameters that affect biogas production are (Nyns, 1985;Kossman & Pnitz 1999a):

1. Anaerobiosis2. Substrate temperature

3. Substrate solid content and agitation4. Retention time5. pH level6. Nitrogen inhibition and C/N ratio7. Available nutrients8. Inhibitory factors.

The different type of bacteria involved in the three stages of biogas production are allaffected differently by parameters 1-8. Since interactive effects between the determiningfactors exists, no quantitative data on the effect they have on biogas production exists. The

following discussion is therefore limited to qualitative effects on biogas production.(Kossman & Pnitz 1999a) At times, it may be practical and useful to see the biogasprocess as a black boxi.e. just observing and recording the inputs and outputs (such asthe amount of dung loaded and the amount of biogas produced). Other times, and whenpossible, observing and recording parameters such as pH-level, temperature and C/N ratiomay be helpful in understanding what is going on inside the black box.

A brief description of the eight parameters and the introduction of notation of keyvariables (that will be used in the following chapters) follows:


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1. Anaerobiosis

Methanogenesis is a strictly anaerobic process. Methanogens do not survive in the

presence of oxygen and hence biogas production requires the absence of air. However, inpractice, small amounts of oxygen will always enter into a digester (mostly through theoxygen present in the influent slurry). As long as the rate of air diffusion into the digesterremains lower than the oxygen uptake rate of the fermentative- and acetogenic bacteria,the process will not be inhibited (Nyns, 1985).

2. Substrate Temperature

In general, increased temperatures lead to quicker biological and chemical reactions. Thisis also true for biogas production but only within the temperature ranges that the

participating bacteria can survive in (Ek, 2007). Anaerobic digestion is in principlepossible between 3C and 70C (Kossman & Pnitz 1999a). It occurs, more or less, in anoptimum way at two temperatures of the substrate: 35C and 55C. The biologicalcommunities responsible for the digestion process at these two temperatures are quitedifferent. In fact, the process and the bacteria involved at different temperatures, isdifferent enough, that three general temperature ranges for anaerobic digestion, havebeen identified (Nyns, 1985):

Psychrophilic (below 20C)

Mesophilic (between 20C and 40C)Thermophilic (above 40C)

The yield, production rate and methane content of the biogas differ significantly betweenthe temperature ranges. Thermophilic digestion results in the highest production ratesand methane content of the biogas (Wellinger, 1999). However thermophilic digestion isalso said to be more vulnerable to changes in temperature (Kossman & Pnitz 1999a), willmost often require heating of the substrate and does not produce higher yields ascompared to mesophilic digestion (Wellinger, 1999). In the mesophilic temperature range,biogas yield increases over-proportionally in the range 20-28C (Kossman & Pnitz1999a). The biogas production rate will also increase with increasing temperature, in themesophilic range. A substrate temperature around 40C is to be avoided, since it is neithersuitable for mesophilic- nor thermophilic bacteria. Psychrophilic digestion results in ratesand yields that seldom will be cost-effective. If the temperature of the substrate is below15C, gas production will be so low that the biogas system will not be economicallyfeasible (Kossman & Pnitz 1999a). The temperature ranges distinguished above are notabsolute. In all anaerobic digestion there will be at least two of the three biologicalcommunities, actively involved in the process at all times (Ek, 2007).

The process of anaerobic digestion is very sensitive to changes in temperature (Kossman &Pnitz 1999a). However, if the change in temperature is slow, it will not have inhibitory


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effects on the process (Wellinger, 1999). The degree of sensitivity, is in turn dependant onthe temperature range of the substrate. Brief fluctuations not exceeding the followinglimits are seen as harmless to the process (Kossman & Pnitz 1999a):

Psychrophilic: (2C/hour)Mesophilic: (1C/hour)Thermophilic: ((0,5C/hour)

In polyethylene small-scale digesters without heating that are situated in tropical regions,mesophilic digestion is pre-dominant.

3. Substrate solid content and agitation

The higher the solid content is the more matter which can be digested is found in the

substrate or slurry (in percent). However, the mobility of the methanogens graduallydecreases with an increased solid content, and the biogas yield may suffer as aconsequence (Kossman & Pnitz 1999a). The solid content of a substrate is defined as themass which remains when the water content is removed (by heating) and is denoted TotalSolids (TS) content (rtenblad, 2000):

TS (in %) = (mass of dry matter / mass of substrate) *100 [Eq. 3.1]

The TS-content varies greatly between, as well as within, different substrates. For cow

dung the TS-content is usually between 10 and 24 % (rtenblad, 2000; Thy, 2003).

The TS-content of the influent is an important parameter which is easily measured inexperiments with biogas production. It is a useful parameter since wet masses are toorelative to compare due to their variable water content. The TS-content is measured afterthe chosen amount of water has been added to the substrate and the influent is ready to beloaded into the digester (For details on measuring techniques for research in the field, seesection 4.2)

The dry matter in the substrate is a mixture of inorganic matter (such as metals andminerals) and organic matter (the biodegradable part). The organic matter content isdefined as the mass which is removed when the dry matter is heated (from 105C to550C) and is denoted Volatile Solids (VS) content (rtenblad, 2000):

VS (in %) = (mass of organic matter / mass of dry matter)*100 [Eq. 3.2]

The VS-content varies depending on the substrate. For cow dung it is generally in therange of 75 to 85 % (rtenblad, 2000).

Agitation of the slurry may have a positive effect on biogas production and at times evenbe crucial to the functioning of a biogas system. Agitation can help to mix fresh substrate


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and bacterial populations, hinder the formation of scum and ensure a uniform bacterialpopulation density in the digester. However, too frequent agitation can also lead todisruption of the symbiotic relationships between the various strains of bacteria and bedetrimental to the process. (Kossman & Pnitz 1999a) Some biogas systems can function

well without any form of agitation.

In a study from Vietnam by An et al. (1997), looking at the effects of agitation in tubularpolyethylene-digesters using pig dung as substrate, concluded that there were noadvantages gained by mixing the contents of the digesters. However, since the results ofagitation are highly dependent on the substrate in use, the frequency and amount ofmixing as well as the method of mixing, biogas systems can only be designed on the basisof empirical data (Kossman & Pnitz 1999a).

4. Retention time - loading rate, process efficiency and system efficiency

The longer a substrate remains in the anaerobic environment of a digester, the morebiogas it will have produced. The amount of biogas produced daily from the substrate willincrease for a number of days (the amount of days, and how fast, will depend on the typeof substrate, its temperature and all other parameters mentioned in this section so far)until it reaches a maximum and begins to slowly decrease. In a continuously fed digester,the Retention Time (RT) is defined as the average amount of days that a unit of substratewill remain in the digester. This is often a valid approximation. However, if the digesterdimensions are greatly altered, the approximation may become invalid.

RT (in days) = Vl/ Vi [Eq. 3.3]

Where Vlis the liquid volume of the digester and Viis the volume of the slurry loaded perday. The Vlof the digester is the volume of the slurry, as compared to Total Volume (VT),which is the volume of the whole digester.

Finding an optimum RT is often a very complex task, involving a careful balancing of theparameters discussed so far. When using cow dung substrate in continuous fed biogas

systems, an RT of 20-30 days is often used (Kossman & Pnitz 1999a).

Directly related to the RT, and the Vlof the digester, is the Loading rate (LR). LR isdefined as the amount of substrate loaded daily (measured in kg TS/day) per liquiddigester volume (measured in m3).

LR [kg TS /day/m3] = (mass of daily influent slurry * TS of influent) / Vl [Eq. 3.4]

LR is an important parameter that can be used when comparing the results of variousstudies since it takes the size of the digester and the TS-content into consideration.


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Biogas production itself can be quantified and compared in different ways. If we first lookat the biogas production rate (BPR) and define it as the amount of biogas (measured inlitres) produced every hour:

BPR [l/h] = Litres of biogas produced per hour [Eq 3.5]

The amount of biogas produced per day is then:

BPd[l] = BPR [l/h]*24[h] [Eq 3.6]

The system efficiency (SE) can then be defined as the ratio of the amount of biogasproduced daily and the digester's liquid volume Vl:

SE (in %) = BPd [l] / Vl [l] [Eq 3.7]

A good system efficiency is reached by experimenting with the RT and the TS-content ofthe influent and finding values that optimize BPd. A high TS-content may at first seemlike a good way to achieve this. However, as is mentioned above, BPd is dependent on ahigh mobility of the substrate in the digester and therefore a not too high value of the TS-content. With unlimited supplies of influent substrate, optimizing system efficiencywould be the only method needed to optimize biogas production (since the amount ofdung used would be of no matter in this case).

If the amount of dung is a limited resource, a good complimentary parameter to measurebiogas production is the process efficiency (PE). The PE is defined as the amount of biogas(measured in litres) produced per unit influent (measured in kg TS):

PE (in l / kg TS) = BPd/ (mi* TS) [Eq 3.8]

Where miis the mass of the influent that is loaded every day and TS is the solid content(as a ratio) of the influent. For practical reasons miis often substituted with vi(since it iseasier to measure volume).

PE (in l / kg TS) = BPd/ (mi* TS) = BPd/ (vi* TS) [Eq 3.9]

The relation between PE and SE basically lies in the chosen RT (and hence the LR and Vl)and the TS-content of the influent. If a comparison of biogas production is conductedbetween two digesters, with the same RT and TS-content of the influent, the choicebetween using PE and SE as an indicator is of no importance the comparative values willbe the same.

One does not necessarily have to use SE or PE as the only two criteria for optimizing a

biogas system. The amount of dung, water and labour that is available as well as anappropriate sizing of the digester (e.g. in relation to available space), can also be important


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criteria to be taken into consideration. In the end it boils down to making sure that biogasproduction of the system is able to meet the biogas demand, a question that will be dealtwith in depth in chapters 5, 6 and 7.

For details on measuring techniques of biogas production for research in the field seesection 4.2.

5. pH level

Methanogens live best in neutral to slightly alkaline conditions (Kossman & Pnitz1999a). Cow dung, as well as other animal dung, is a non-acidifying biomass substrate, andwill very seldom lead to acid conditions (Nyns, 1985). Once the process of digestion hasstabilized, the pH will normally take on a value between 7 and 8.5 (Kossman & Pnitz1999a).

6. Nitrogen inhibition and C/N ratio

All substrates contain nitrogen. Under alkaline conditions, even a relatively low nitrogenconcentration may inhibit the process for a time. However, methanogens are quiteresilient and can over time adapt to higher levels of nitrogen concentration. Mostimportant is that the ammonia (NH3) level does not exceed 200-300 mg NH3per litresubstrate (Kossman & Pnitz 1999a).

Microorganisms require both nitrogen and carbon for their cell growth. Experiments haveshown that the metabolic activity of methanogens can be optimized at a C/N ratiobetween 8 and 20, depending on the substrate. For cow dung the optimum C/N ratio issaid to be around 18. (Kossman & Pnitz 1999a) However, the actual effect of the C/Nratio on the metabolism of microorganisms is very hard to quantify. This parameter istherefore of comparative low interest in relation to the other parameters discussed so far.(Smrs, 2009)

7. Available nutrients

In order to grow, bacteria need more than just a supply of organic substances. In additionto carbon, oxygen and hydrogen, the generation of biogas requires a supply of mineralnutrients, such as, nitrogen, sulphur, phosphorus, and potassium, as well as, a number oftrace elements, such as, iron, zinc, and nickel. Most substrates, including cow dung,include these substances. If the concentration of any individual substance is too high itmay have an inhibitory effect on the process. (Kossman & Pnitz 1999a)


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8. Other inhibitory substances

Besides the inhibitory effect of high concentrations of mineral nutrients and heavy metals(as mentioned above), antibiotics and detergents used in livestock husbandry can have

inhibitory effects on the process of biogas production.

3.2.2.2 Other Important Process ParametersThe following parameters do not affect the magnitude of the biogas production but arestill highly important process parameters:

1. Methane content of gas (the quality of gas)

As has been mentioned, biogas is essentially composed of Methane (CH4) and Carbon di-

oxide (CO2). When biogas is combusted, transformation of CH4 to CO2 releases energy inthe form of heat. The CH4content of biogas is therefore a good indicator of the quality ofthe gas in terms of combustion. The CH4content of biogas varies significantly dependingon the substrate digested, the substrate temperature and more. Cow dung digested undermesophilic conditions, produces a biogas with a CH4content of around 65 % (55 to 75 %)(Kossman & Pnitz 1999b; rtenblad, 2000; Thy, 2003). For details on measuringtechniques for research in the field, see section 4.2.

2. Ammonia-content of influent and effluent

The process of anaerobic digestion changes the chemical, biological and physicalproperties of the slurry. The viscosity generally increases due to the transformation of thecarbon in the dung into CH4 and CO2, the odour decreases and the amount of pathogensdecreases. The fertilizer value of digested slurry is generally higher than undigestedbiomass substrates and can lead to higher yields. (Kossman & Pnitz 1999b; rtenblad,2000)

Among the many reactions resulting from anaerobic digestion, the metabolisation oforganic nitrogen into mineralized nitrogen (aka Ammonia or NH3), is one of the mostimportant in terms of the fertilizer value. NH3is directly available to plants and istherefore also known as plant-available nitrogen. The organic nitrogen remaining in thedigested slurry must be mineralized by soil bacteria before it is available to plants(rtenblad, 2000). Measuring the NH3-content of the influent and effluent, and observingthe difference, is a good and fairly simple way to quantify the improvement in terms offertilizer value, resulting from anaerobic digestion (Thy & Preston et al., 2003).

Besides being a good organic fertilizer, digested slurry also has soil improving qualities.Substances such as protein, cellulose and lignin contribute to increasing a soils

permeability and hygroscopicity while preventing erosion and improving agriculturalconditions in general (Kossman & Pnitz 1999a).


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The NH3-content of fresh cow dung will of course vary depending on a cows diet. Anaverage of 2,6 kg/ton can be found in literature. Digested slurry has an average NH3-content of 3,3 kg/ton. (rtenblad, 2000) For details on measuring techniques for research

in the field see section 4.2.

If the digested slurry is not used directly after it leaves the digester (e.g. left to dry), therewill be a loss of its fertilizing properties, mainly due to the evaporation of NH3. Thedigested dung should therefore preferably be used rather quickly (or covered) if it is to beused as a fertilizer. (rtenblad, 2000)

3.3 System Design

In China, the majority of the installed biogas systems are of the fixed-dome design and inIndia, the most common design is a floating dome. Both of these system designs are madeof cement and both the construction and installation require extensive knowledge andexperience. (Kossman & Pnitz; An et al., 1997) The price of these systems is also seen asone of the major constraints to their diffusion (An, 2002), especially in countries wherelittle government support can be expected (Gustavsson, 2000).

3.3.1 Appropriate Biogas Technology

In response to this, the tubular plastic digester was developed in the early 1980 byPreston and Botero (Botero & Preston 1987), based on the Taiwan modelas described byPound et al. (1981). The cost of construction and installation was more than 5 times lessthan the systems previously used (34- 60 USD compared to 180-340 USD) and henceappropriate for use by farmers in poor rural areas, in countries without large supportprograms. The technology specifically spread quickly in Vietnam. Within 10 years morethan 20,000 tubular plastic digesters were up and running. Animal dung (from cows andpigs) is the most common substrate used in these systems. These systems are easier toconstruct, install and maintain than the floating dome and fixed dome designs. (An, 2002)However, there have also been a number of problems identified (see section 3.3.3 below).

3.3.2 Polyethylene Plastic Biogas Systems

The design and the materials used for polyethylene plastic biogas systems vary slightly butin general you need: Polyethylene plastic, PVC pipes, flexible plastic pipes, a bucket,manual ball-valves, plastic bottles, rubber, tape, thin rolled metal, and hardware allreadily available in most local hardware and agricultural supplies stores around the world.A design overview of a tubular plastic biogas system can be seen in Figure 3.2.


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Figure 3.2: A design overview of a tubular plastic biogas system.

Here follows a brief description of the components of the biogas system and theirfunction.

Inlet bucket(with stirrer)The substrate needs to be mixed with an appropriate amount of water before it is loadedinto the digester. An inlet bucket out of metal, with a plug in the bottom is often used forthis purpose. The stirrer is manually operated and can be as simple as a bamboo pole.

DigesterThe digester is at the heart of the biogas system. This is where the slurry (mix of substrateand water) spends a number of days, produces biogas, and then is let out the other end.The digester is constructed out of transparent plastic film, preferably UV-coated

polyethylene plastic.

Inlet and outlet pipesThe inlet and outlet pipes are usually constructed out of PVC pipes and inserted into eachend of the digester and sealed off using rubber and tape. The inlet pipes and outlet pipesmust be below the slurry level at all times to avoid leakage. The outlet pipes height isadjusted at installation to obtain an appropriate slurry level in the digester. A plug may beattached to both the inlet and outlet pipes to be able to regulate when the slurry is to flow(this digester design is known as plug-flow, as opposed to continuous flow).


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Gas pipesThe gas pipes transport the gas from the digester to the gas holder and on to the stove. Thepipes need to be well attached to the digester, gas holder and stove in order to minimizeleaks. The gas pipes can be constructed from different materials. PVC pipes and flexible

plastic pipes (hoses) are both common. Depending on the material, diameter and length ofthe pipes, friction will generate a pressure drop in the gas when it moves from the digesterto the stove.

Safety ValveA safety valve ensures that the pressure in the biogas system does not reach levels thatwill risk making the digester or gas holder break. If the gas in the gas holder is not usedfor a while, and the pressure reaches the determined upper pressure limit, gas will leakout to the atmosphere through the safety valve. The upper pressure limit is set byadjusting the water level in the valve. The Safety valve also functions as a water trap,

preventing water from condensation to block the gas flow in the gas pipes. Therefore,safety valves should be placed at the lowest point of the gas pipes leading from thedigester to the gas holder (Ref 7, Ref 11). Safety valves can be constructed in differentways, using different materials but a common way is to use a used plastic bottle and PVCpipes.

Biogas HolderThe gas holder is, just as the digester, often constructed out of UV-coated polyethyleneplastic and is used as a reservoir for the gas before it is burnt in the stove. The gas holder

will increase the biogas flow to the stove since the volume of biogas in the system will belarger than without having a gas holder (Kossman & Pnitz 1999a). Most gas holderspreviously used in tubular plastic biogas systems, have been positioned horizontally andweights have been put on top of it to increase the pressure of the gas.

StoveThe biogas stove is the last component of the biogas system and can be either acommercial burner or of a simpler home-made design. An air-intake or mixing chamber isnot necessary but may increase the efficiency (but also the cost). The simplest stovedesigns simply have a manual valve to regulate the flame and a manifold to create a wellshaped flame. They are constructed of sheet metal of various kinds.

3.3.3 Identified problems, critique and failure of polyethylene digesters

A number of problems with tubular plastic biogas systems, have been identified, andwritten about in literature. One of the main problems is the durability and life-time of thematerials (the polyethylene used for digesters and gas holders and the plastic used for thegas pipes) and their sensitivity to UV-rays and material damage from falling objects,people and animals (An, 2002; Van Chinh, 2002; Kossman & Pnitz 1999a; Kossman &

Pnitz 1999b; United Nations, 1984). The polyethylene digester is also difficult to repair ifdamaged (Kossman & Pnitz 1999b). Another problem is the low pressure, gas flow and


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production rate often experienced (Cortsen et al., 1997; United Nations, 1984). The landarea required for installation is also larger than for other designs (Van Chinh, 2002). Leaksfrom the seals between gas pipes and digester have also been known to occur.

3.3.4 Improved Polyethylene Plastic Digesters in Lembang

Since the biogas initiative started in 2007, a number of these problems have beenaddressed, and solutions have been found by the biogas team in the Lembang area.

The plastic film used for constructing both the digesters and the gas holder is UV coated,meaning that it is not as sensitive to UV-rays as regular polyethylene plastic. The plasticfilm used is also thick enough that one layer is enough (reducing costs). To further protectthe plastic from sunlight, both the digester and the gas holders are covered with anadditional thin plastic film, known locally as Mulsa. Mulsa is used in agriculture to

retain heat and moisture in the soil around crops. Because of its insulative qualities, theMulsa also helps increase the process temperature of the digester.

By using a plastic sealer, the shape of both the digester and gas holder can be made morelike a cylinder (see Figure 3.3). For the digester, this ensures a tighter fit to the inlet andoutlet pipes, and for the gas holder it ensures that it can be completely emptied if needed.The gas holders in Lembang are also positioned vertically (an idea pioneered in Vietnam)instead of horizontally, so that weights can hang from the bottom of it, to increase the gaspressure as it is emptied.

Pressure valves are another improvement introduced by the team in Lembang. In earlierplastic tubular biogas system designs, pressure valves are not included. However, they canbe very useful, as they allow the user to adjust the pressure of the gas in the digester (bychanging the water level in the pressure valve). They also ensure that when the gas holderis emptied (i.e. the stove is being used), the pressure of the gas can be regulated to a higherdegree and the gas pressure in the digester will never go below the level indicated by thepressure valve (since the gas will only flow in one direction through the pressure valve).The pressure valve is constructed with the same material as the safety valve and should beplaced close to the gas holder (for easy access). The safety valve and pressure valve have

also successfully been integrated into the same device, by using two pipes of differentdiameter and length and inserting them into each other (see Figure 3.3).


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Figure 3.3: A digester constructed using a plastic sealer ensures a cylindrical shape and a tight fit of theoutlet and inlet pipes. An integrated safety and pressure valve with the flow of gas indicated by the blackarrows. The white box highlights the end of the safety valve, which surrounds the white pipe which acts asa pressure valve.

Leaks from the attachment point of the gas pipe to the digester are minimized by a sealmade of rubber from old bicycle tires, PVC plates, a metal valve, nuts and bolts. The gas

pipes used are also made of a flexible hose-like material, making the connection to thedigester easier (less weight on the connection). The flexible gas pipe is also less sensitive toUV-rays and mechanical damage, as compared to PVC pipes.

The stoves used for the systems in the Lembang area are made of stainless steel andconstructed locally in a metal shop. The cost of the stove is around Rp. 100,000 (10 USD),which is relatively low compared to commercial alternatives.


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4. Materials and Methods

A wide range of methods and materials were used to close in on the research questions

presented in section 2.3. The technical aspects of constructing and designing communal-and single-family biogas systems were investigated with the help of a number ofexperimental set-ups presented in section 4.1. The measured variables and measuringtechniques are then presented in section 4.2. In section 4.3, two villages with biogassystems that are in use and which were used to evaluate the functionality of real systems,are briefly described.

4.1 Experimental Set-up s

In order to investigate the technical aspects of developing communal biogas systems, aswell as improving single-family systems, a number of experimental set-ups wereconstructed and installed in the village of Cicalung. The set-ups ranged significantly insize (from small all the way up to full-scale). The experiments run on these set-ups aredocumented mostly in chapter 5, but a small part of Chapter 6 is also based onobservations of some of these set-ups.

4.1.1 Small-Scale Experimental Digesters in Saung Richie (A)

Small-scale experimental digesters where constructed in order to run a number ofexperiments that would be very difficult and time consuming to conduct on full-scale.These experiments are documented in Chapter 5.

Construction and InstallationEight small scale digesters where built in a field made available by a local farmer inCicalung. They were protected from weather and wind by a Saung (a bamboo structurecovered with transparent polyethylene plastic). Each digester was connected to a gasholder via a pressure valve and a safety valve. The gas holders where dimensioned largeenough so that gas production measurements would not need to be conducted more thantwo times per day. The materials used to construct the experimental digesters did notdiffer much from the materials used in real systems. Figure 4.1 shows the constructedSaung and four of the digesters, pressure valves and safety valves.


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Figure 4.1: The SaungRichie with digesters A1-A6. Digester A3a, A3b, A3c and A4.

For ease of reference each of the experimental digesters were given a name:

Digester A1: A standard dimensioned digester covered with soilDigester A2: An uncovered standard dimensioned digesterDigester A3a: A standard dimensioned digester, 1st of the connected digestersDigester A3b: A cement digester, 2nd of the connected digesters, in between A3a and A3cDigester A3c: A standard dimensioned digester, last of the connected digestersDigester A4: A standard dimensioned digester, covered with rice husksDigester A5: A shorter and wider digesterDigester A6: A vertical digester with the same dimensions as A5.

Inoculation and OperationEach digester was inoculated with a mix of fresh dung and water (1:1 Ratio ) and alreadyprocessed slurry (known as starter), taken from the output of Digester C (see below). Theywere filled with an amount of slurry that was thought to result in a liquid volume of 80%.Later, measurements of the total volume of the digesters resulted in liquid volumes thatdiffered from this. The digesters where then left to stabilize for two weeks before dailyloading commenced. Each digester was then loaded every morning with an equal mix offresh dung and water that resulted in a RT of 30 days. The calculated LR (inkg/TS/m3/day) was based on measurements of average TS-contents of the dung using ahydrometer (see section 4.2). An overview of the experimental digesters design and

operation specifics can be found in Table 4.1.


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Table 4.1: Design and operational specifics of small-scale experimental digesters A1 to A6. The difference in

liquid volume (in % of total volume) of the digesters at the start of the experiments is a result of incorrectapproximations of the total volume which were corrected later. The loading amount is calculated to result ina RT of 30 days in all digesters. As for the LR, 1 liter of influent slurry is assumed to equal 1 kg since amajority of the slurry is water (over 90 %). Digesters A3a, A3b and A3c differ a bit from the rest, since theyare connected to each other. Only A3a is loaded daily, and with an amount of slurry that will result in acombined RT of 30 days (10+10+10) for the connected digesters.

4.1.2 Communal Prototype Digester (B)

A communal biogas system supplying biogas to two households from one digester was

installed in the village of Pasir Angling in January of 2009. For further information on thevillage of Pasir Angling and details of the biogas systems there, see section 4.3. Due to thedifficulties of experimenting on this system while it is in use and to measure gasproduction from a full scale system, a communal prototype digester (digester B) wasconstructed and installed in the village of Cicalung. Digester B was meant to answerquestions related mainly to distribution of gas flow which is documented in section 5.3and discussed in section 6.3.

Construction and InstallationDigester B was based on the communal system that had just been installed in the village

Pasir Angling which consisted of one long tubular digester and two gas holders, supplyingbiogas to two different households. It was installed next to the Saung with digesters A1-

Digester

A1Digester

A2Digester

A3aDigester

A3bDigester

A3cDigester

A4Digester

A5Digester

A6

Length [m] 1 1 1 0.91 1 1 0.59 0.59

Diameter orwidth*height [m] 0.3 0.3 0.3 0.21*0.35 0.3 0.3 0.42 0.42

Total Volume [l] 70.7 70.7 70.7 66.9 70.7 70.7 81.7 81.7

Liquid Volume atstart [l] 55.8 55.8 55.8 55.8 55.8 55.8 69.3 69.3

Liquid Volume atstart [%] 78.9 78.9 78.9 83.4 78.9 78.9 84.8 84.8

LoadingFrequency Daily Daily Daily - - Daily Daily Daily

Loading amount[l/day]

1.86 1.86 5.58 - - 1.86 2.31 2.31

Water:Dung ratio 1:1 1:1 1:1 - - 1:1 1:1 1:1

Loading rate [kgTS/m3/day] 2.72 2.72 8.17 - - 2.72 2.72 2.72

Retention time[days] 30 30 10 10 10 30 30 30


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A6 (see Figure 4.2). Two gas holders were also constructed and connected to the digestervia pressure valves. The pressure valves where especially designed so that the watercolumn could be adjusted to a high order of accuracy (


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Digester

Pasir Anglingcommunal digester

(PA1)

Digester B(communal prototype

digester)

Length [m] 7 3.5Circumferance [m] 4 2

Diameter [m] 1,27 0.64Total Volume [l] 8913 1114Liquid height [%] 70 70Liquid Volume [l] 7702 963Liquid Volume [%] 86.4 86.4Length/Diameter ratio 5.5 5.5Wanted RT [days] 30 30Required Loadingamount [l/day] 256.7 32.1Water:dung ratio 1:1 1:1Loading rate [kgTS/m3/day] 2.72 2.72Loading frequency ? Daily

Gas Holders

Length [m] 1.5 0.75Circumferance [m] 3 1.5Diameter [m] 0.95 0.48length/diameter ratio 1.57 1.57Width [m] 0.75 0.38Volume [l] 1074 134Total volume [l] 2148 268

Gas Pipes

Typeflexible plastic tube flexible transparent plastic tube

Material ? ?Diameter [cm] 1.91 0.7

Pressure and Safety Valves

Integration yes noMeasurement scale no in [mm]

Table 4.2: Comparison of design and operational specifics between digester B (communal prototype digester)and the communal system installed in the village of Pasir Angling (PA1). Integration of pressure valves andsafety valves means they are built into the same device (see section 3.4 for a picture and explanation).

4.1.3 Wawas Full-Scale Digester (C)

Small scale models of biogas systems, such as the digesters A and B above, are useful whenrunning experiments that are difficult to conduct on full scale systems or systems in use.However, certain experiments, such as measuring production rates, really require that afull scale system is used. Fortunately, a biogas system in Cicalung that has been in use forover two years, was made available for experimentation. The experiments andmeasurements conducted on digester C are documented in section 5.4 and 6.4.


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Construction and InstallationThe system was constructed and installed over two years ago as one of the firstpolyethylene tubular biogas systems in the Lembang area. The system was installed in thebackyard of Wawa Wahyudisfamilys house. Originally it was designed and dimensioned

to provide two households with biogas, but is today only used by Wawas family (ahousehold with 3 people) and for conducting experiments. The different parts of thebiogas system can be seen in Figure 4.3.

Figure 4.3: Digester C with influent bucket full. A full gas holder and hiding behind it - an emptied gasholder with weights to increase the pressure of the gas, and the pressure valve to the right. Adjusting theflame on the biogas stove in Wawas household.

OperationSince there is limited access to water on the plateau where the village of Cicalung issituated, there are not many cow farmers in the area. The closest cow farmer to Wawas

families household is Mr. Akang who lives in a nearby village, a 10 minute walk away.Mr. Akang has two biogas systems installed but does not manage to use all of the dungthat his cows produce, in his systems. For the last two years, digester C has not been

loaded on a daily basis and at times quite sporadically. In general, the digester was loadedwith as much as 300 l of dung at a time (making 600 l of slurry) but only every two weeks.This would equal a loading amount of approximately 43 l per day and results in a RT ofaround 118 days. Before measurements commenced, the LR was changed in order to havea RT of around 30 days. 80 l of dung was picked up every morning at Mr. Akangsandloaded into the digester with a dung:water ratio of 1:1, resulting in 160 litres of slurrygoing into the digester every day. This loading routine was started more than 30 daysbefore measurements began and maintained throughout the experimental period. Figure4.4 shows the process of loading the digester.


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Figure 4.4: Early morning dung pick-up. Carrying water to the digester. Mixing water and dung in theinfluent bucket.

The design specifics of digester C and the operational specifics during the experimentalperiod, can be found in Table 4.3.

Table 4.3: Design specifics of digester C and operational specifics before and during the experimental period.

Digester C

Length [m] 10Circumferance [m] 3

Diameter [m] 0,955Total volume [l] 7162Liquid Volume [l] 5053

Liquid Volume [% of total volume] 70,6Loading frequency Daily

Loading amount [l/day] 160Loading rate [kg TS/m3/day] 2,587Retention time [days] 31,58

Gas Holder

Circumferance [m] 3Height [m] 1,5Volume of full holder (cylinder) [l] 1074


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4.2 Measured Variables and Measurin g Techn iques

Considering the applied nature of the experiments and the limited resources available, theamount of variables that can be measured and the accuracy of the measurements are

limited. Simple measuring techniques for research in the field were studied and therequired measuring equipment was either purchased in Sweden and then brought toIndonesia, or purchased or constructed on the spot in Bandung. Most variables mentionedbelow were measured in every experiment conducted. However, in many experiments,several variables did not contribute much to the understanding of the studied phenomena,and were therefore excluded from the experimental description in Chapter 5. Below,follows a review of the measured variables as well as a description of the measuringtechniques and equipment.

4.2.1 Biogas Production RateBiogas production rate (BPR) is the volume of biogas that is produced per unit time.Biogas BPR was the most crucial variable measured and the results ended up being used inalmost all of the experimental descriptions.

Measuring technique and measuring equipmentBPR can be measured in a number of ways. Flow-meters have been used in earlierexperiments and were an option considered (United nations, 1984). A flow-meter wasbrought from Sweden but ended up not being used. Instead a technique known as Water

Displacement was used. This is a simple technique to measure BPR that has been used in anumber of earlier experiments on tubular plastic biogas digesters (Thy et al., 2003; Thy etal., 2005; Kounnavonga, 2008). The basic principle is to let biogas fill a light-weightbucket of known volume, turned up-side-down and floating in a larger, water-filledbucket. As more biogas enters the light-weight bucket, it rises, and the volume of theproduced biogas per unit time can be calculated (since the volume of the light-weightbucket is known). Two water displacement units were constructed for the experimentalset-ups. A smaller unit was constructed to measure the volume of the biogas producedduring the experimental periods of digesters A1-A6 and digester B. Later, a much largerunit was constructed in order to measure the volume of the biogas produced from the full-scale system (digester C).

Construction and installation of the smaller water displacement unit WD unit AB)To be able to measure biogas production from digesters A1-A6 and digester B, there was achoice in either constructing one Water Displacement unit (WD unit) per digester(meaning 9 in total) or, creating a single WD unit that could measure the volume of biogasproduced from all digesters (one at a time). The latter was chosen, as it seemed to be theeasiest and cheapest alternative. The design of WD unit AB and the materials required aremost easily understood by studying Figure 4.5 below.


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Figure 4.5: The small water displacement unit (WD unit AB) used to measure the biogas produced from

digesters A1-A6 and digester B. The biogas was pumped from each gas holder into the unit by using thepump seen on the left in the picture.

The larger bucket was built from a hard, albeit flexible, plastic sheet that was rolled into acylinder and a poly-ethylene sock that was inserted into it. Through the bottom of thesock a pipe was installed that would reach above the water level in the bucket. The top

of the WD unit was created using a light-weight, transparent, plastic sheet that wasflexible enough to allow it to be bent and folded into a cylinder open only on one end(using glue and tape). The top was dimensioned to be able to hold at least 25 litres ofbiogas (the approximate size of the gas holder of digesters A1-A6). By knowing the

circumference of the light-weight plastic top, a scale (in litres) was constructed and tapedto its side (see Figure 4.6). WD unit AB was installed in the Saung next to digesters A1-A6. A hole was dug and necessary piping and manual valves where connected to the unit.

Operation of WD unit ABBefore the gas holders belonging to digesters A1-A6 and digester B where emptied, theywere detached from the system (manual valves ensured that no gas leaked from the gasholder or the digester at this time) and connected to the WD unit AB, via a manual pump.Before the measurement started, it was made sure that the light-weight plastic top of WD

unit AB was at its s

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Communal Polyethylene Biogas Systems