esity

a r t i c l e i n f o

Article history:Received 31 December 2012Accepted 30 March 2013Available online 6 May 2013

Keywords:Residual municipal solid wasteAlternative treatmentLife cycle energy balancePrimary energyWaste to energyMechanical biological treatment

a b s t r a c t

cal heat treatment (e.g. Papageorgiou et al., 2009; Arena, 2012).The waste renery concept is another alternative that has beenmaterialised in Denmark through the Renescience technology(Tonini and Astrup, 2012).

and assumed process efciencies across treatment chains. In gen-eral, no consensus has been reached, as both alternative treatmentstrategies are found to be preferable in different conditions and re-gional settings.

For example, Consonni et al. (2005a,b) compared four genericscenarios based on waste management strategies implemented indifferent regions of Italy. The rst strategy, in which residual wasteis treated directly in a conventionalWtE plant, is compared to strat-egies where the waste is subjected to a light mechanical treatmentfollowed by waste incineration (strategy 2), mechanical biological

Corresponding author. Address: Institute of Chemical Engineering, Biotechnol-ogy and Environmental Technology, Faculty of Engineering, Niels Bohrs Alle 1, DK-5230 Odense M, Denmark. Tel.: +45 2440 9882.

Waste Management 33 (2013) 16481658

Contents lists available at

Waste Man

elsE-mail address: cic@kbm.sdu.dk (C. Cimpan).1. Introduction

The well-established alternatives to treating mixed or residualmunicipal solid waste (MMSW) today are mass grate combustionor thermal Waste-to-Energy (WtE), different MechanicalBiological Treatment (MBT) concepts followed by energy recoveryand direct disposal through landlling. Many less proven alterna-tives also exist, such as waste pyrolysis, gasication and mechani-

A number of studies have been dedicated to comparing the en-ergy efciency and overall environmental performance of directWtE and MechanicalBiological Treatment congurations (e.g.Consonni et al., 2005a,b; Christensen et al., 2009; Papageorgiouet al., 2009; Koci and Trecakova, 2011; Ketelsen, 2012).Zeschmar-Lahl (2010) made a review of six studies performed inGermany between 2003 and 2009. Results vary widely betweenstudies, depending on system boundaries, background conditions0956-053X/$ - see front matter 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.wasman.2013.03.026Primary energy savings potential is used to compare ve residual municipal solid waste treatment sys-tems, including congurations with mechanical (MT) and mechanicalbiological (MBT) pre-treatment,which produce waste-derived fuels (RDF and SRF), biogas and/or recover additional materials for recy-cling, alongside a system based on conventional mass burn waste-to-energy and ash treatment. To exam-ine the magnitude of potential savings we consider two energy efciency levels (state-of-the-art and bestavailable technology), the inclusion/exclusion of heat recovery (CHP vs. PP) and three different back-ground end-use energy production systems (coal condensing electricity and natural gas heat, Nordic elec-tricity mix and natural gas heat, and coal CHP energy quality allocation).The systems achieved net primary energy savings in a range between 34 and 140 MJprimary/100 MJinput

waste, in the different scenario settings. The energy footprint of transportation needs, pre-treatment andreprocessing of recyclable materials was 39.5%, 118% and 18% respectively, relative to total energysavings. Mass combustion WtE achieved the highest savings in scenarios with CHP production, nonethe-less, MBT-based systems had similarly high performance if SRF streams were co-combusted with coal.When RDF and SRF was only used in dedicated WtE plants, MBT-based systems totalled lower savingsdue to inherent system losses and additional energy costs. In scenarios without heat recovery, the biodry-ing MBS-based system achieved the highest savings, on the condition of SRF co-combustion. As a sensi-tivity scenario, alternative utilisation of SRF in cement kilns was modelled. It supported similar or highernet savings for all pre-treatment systems compared to mass combustion WtE, except when WtE CHP waspossible in the rst two background energy scenarios. Recovery of plastics for recycling before energyrecovery increased net energy savings in most scenario variations, over those of full stream combustion.Sensitivity to assumptions regarding virgin plastic substitution was tested and was found to mostlyfavour plastic recovery.

2013 Elsevier Ltd. All rights reserved.Energy implications of mechanical and mcompared to direct waste-to-energy

Ciprian Cimpan , Henrik WenzelInstitute of Chemical Engineering, Biotechnology and Environmental Technology, Univer

journal homepage: www.All rights reserved.chanicalbiological treatment

of Southern Denmark, Denmark

SciVerse ScienceDirect

agement

evier .com/ locate/wasman

duced and avoided ows are included from the initial induced

alent of each process specic energy and material input is ac-

anastabilization MBS (strategy 3) and classical composting MBT(strategy 4), both followed by refuse-derived fuel (RDF) utilisationin a uidized bed combustor. Comprehensive mass and energy bal-ances showed that additional energy use and specic losses duringprocessing determined lower energy savings in all alternativescompared to direct WtE. In a subsequent study, Consonni et al.(2006) added co-combustion of RDF in coal-red power plantsand utilisation in cement kilns. Both alternatives showed similaror better energy savings compared to conventional WtE. These re-sults were recently augmented by Rigamonti et al. (2012), sup-ported by long term monitoring in a coal-red power plant.

Wallmann et al. (2008) calculated the energy efciency of dif-ferent MBT concepts (MBT with composting, -with biogas and bio-logical drying MBS) by making primary energy balances based onoperational data from 18 to 20 plants. System boundaries startedat plant and ended with the outputs generated. Electricity, gasand diesel used in plant operation were converted to primary en-ergy by using coefcients that account for the cumulated energydemand of their production and supply. The calculation stoppedat considering the energy content of energy carrying outputs (i.e.RDF and biogas) as primary energy further available. Resultsshowed that, on average, 5972% of the energy invested in theMBT systems was available in their outputs. Ketelsen (2012) devel-oped a balancing model which calculates energy efciency and cli-mate-relevant CO2 emissions for process combinations using MBTtechnologies. Input data from 15 facilities (MBT plants) was used tocalculate the respective parameters and then make an overall com-parison to direct thermal treatment of waste. Results reected agreat variability in energy efciency and CO2 footprint betweenMBT plants and their extended energy recovery systems. On aver-age, however, MBT waste management systems had an advantageover direct thermal treatment.

Material recovery from municipal solid waste has been, on theone hand, addressed in many comprehensive studies which com-pare different source separation and collection methods (e.g.Dahln et al., 2007; Larsen et al., 2010; Bernstad et al., 2011). Nev-ertheless, considerable amounts of recyclable materials are left inthe residual stream even in waste management systems withextensive separate collection. On the other hand, studies which as-sess residual waste treatment strategies are usually focused on en-ergy recovery alternatives and their efciencies and are recurrentlyhandling resource recovery in a generic and limited way. Van Berloand De Waart (2008) compared variants of landlling and variantsof WtE by using an array of different performance indicators suchas primary resources, diversion rate, energy efciency, the R1-formula, exergy efciency and CO2 balance. Advantages andshortcomings of the different methods of evaluation are discussedtogether with the relevance of their results. The study concludedthat performance indicators that combine conversion efciencyto energy products with resource efciency (substitution of pri-mary materials) and application efciency (e.g. quality of energy)can offer a more comprehensive base for development strategiesin waste management.

Mechanical and mechanicalbiological treatment processesmanipulate and convert raw waste into different streams whichare directed either to material recycling, energy recovery or dis-posal. They create opportunities to recover additional resourcesand broaden the range of possible energy recovery applications,including high efciency industrial processes. However, they alsoincrease system complexity, they add inherent system losses andinduce additional energy consumption. Considerable research hasyet to be dedicated to demonstrate the environmental, resourceand socio-economic relevance of these alternatives (Velis and

C. Cimpan, H. Wenzel /Waste MCooper, 2013). In the present study ve residual waste treatmentsystems are compared from a holistic perspective by means of lifecycle energy balances. The main objective was to contribute to thecounted for, and outputs are modelled by efciency coefcientswhich determine intermediary to nal outputs. Any transport/transfer from one unit process to another has been accounted foras energy (diesel) consumption by transportation.

The ve alternative systems assessed in this study are describedin detail in Section 2.2. The essential difference between alterna-fuel/ore extraction to the nal avoided fuel/ore extraction, thusproviding an account of all cumulated energy along the wholechain of operations. This energy accounting is also expressed asthe primary energy balance. Hence, induced and avoided materialstreams are also converted and expressed as the energy value ofall induced/avoided fuel and feedstock in their supply chain. Theresult of the life cycle energy balance is a net quantity of primaryenergy, expressed as kgoil eq. or MJprimary per unit processed waste,which in turn is the difference between total primary energy in-duced and total primary energy avoided by that system.

2.1.1. System boundariesUpstream burdens for the production and use of the materials

that end up in waste are not considered based on the zeroburden assumption used in LCA of waste management systems(Ekvall et al., 2007). System boundaries are illustrated in Fig. 1.Alternative treatment systems start at the point of waste genera-tion, with collection and transport of waste to the rst system pro-cess, namely pre-treatment. Intermediary products generatedduring pre-treatment are sent to further rening, energy recoveryor directly to disposal. Secondary wastes arise at this point (e.g.sorting residues, bottom ashes) which are reprocessed or directlydisposed of. In the third step, material streams (i.e. metals andplastics) are reprocessed to secondary materials. Secondary pro-duced materials and recovered energy replace primary materialsproduced from virgin sources and background energy production,on their respective markets. Secondary waste ows arising in nalreprocessing were not included in the model.

For each unit process in the system, the primary energy equiv-understanding of energy and resource efciency of such complexintegrated systems considered alternatives to conventional WtE.The magnitude of potential savings was examined consideringdifferent technological energy recovery alternatives, variation inenergy recovery efciency and the inuence of different back-ground conditions and end-use energy production.

2. Methodology

2.1. Life cycle energy balance

The comparison of alternative systems for residual waste treat-ment has been addressed in this study by performing a completelife cycle energy balance for each system. Each system consumesmaterials and energy in order to operate, accounted for as systemburdens or induced ows. During the treatment process, recoveredand utilised materials and energy are generated, and accounted foras functional outputs from the system. These functional outputsare modelled to include the markets at which they are sold andat which they replace alternative supplies of the same functionaloutputs. The scope of the modelled system is, then, expanded to in-clude these replaced alternative ows, also called avoided ows.The waste treatment system is, thus, credited with substituting asimilar amount of materials or energy produced from primarysources. Similar to full Life Cycle Assessment (LCA) studies, all in-

gement 33 (2013) 16481658 1649tives is the pre-treatment step, while energy recovery and materialreprocessing steps are dened in a set of common scenarios. Massand energy ows within pre-treatment processes are based on

is only feasible by choosing background energy systems and using

del

anaspecic yearly operational data from three plants described inSection 2.2.1. Due to small differences between the plants, in thecaloric value of the input waste processed, it was assessed thatenergy balances per tonne input are not directly comparable. Afurther normalisation of the primary energy balance results wasapplied, whereby consumption and savings were quantiedrelative to energy content of input waste. Results both beforeand after normalisation are presented in the results section of thispaper.

2.1.2. Efciency levels of compared technologiesWaste-to-energy plants in this investigation comprise of (1)

Fig. 1. Conceptual system mo

1650 C. Cimpan, H. Wenzel /Waste Mconventional mass grate thermal treatment plants and (2) dedi-cated, so-called RDF mono-combustion plants. They have consider-ably different energy efciencies across Europe depending on avariety of factors including the age and size of plants, location,which is crucial for possibilities to market energy outputs, andthe existence of national incentive programmes which supportoptimisation and technological advances in energy recovery. Thisis shown by studies that have reviewed large numbers of wasteincineration plants, such as that of Reimann (2009) and Grossoet al. (2010).

In this study both RDF and SRF (solid recovered fuels) denotecombustible, high caloric value waste mixtures separated bymechanical treatment from residual waste, however, with theimportant distinction that SRF is prepared to meet certain qualityrequirements which make it suitable for advanced energy recoveryapplications such as co-combustion with conventional fossil fuelsin industrial plants (Velis et al., 2010).

In order to reect the wide range of variation found in energyefciency of waste-to-energy plants across Europe, and to allowcomparisons of alternatives on an equal footing, two main techno-logical efciency scenarios have been dened:

SotA (State-of-the-Art): Energy recovery efciency equals theaverage of new WtE plants constructed in Europe. RDF/SRFstreams are modelled used in mono-combustion plants.

BAT (Best Available Technology): Energy recovery efcienciesequal the best case WtE in operation today. SRF streams areco-combusted with coal in coal-red power plants.These main technology scenarios have two variations: (1) heatutilisation is possible and WtE includes CHP production, (2) heatutilisation is not possible and WtE includes only electricity or PPproduction. Technologies and selected efciencies are described indetail in Section 2.2.2.

2.1.3. Background or primary energy productionThe primary energy demand to produce end-use energy such as

electricity and heat, differs to a large extent based on the conver-sion technology and source of primary energy used (e.g. coal, nat-ural gas, renewable). As such, a comparison of waste treatmentsystems based on their potential for primary energy substitution

for residual waste treatment.

gement 33 (2013) 16481658them as the reference against which energy production from wasteis assessed, i.e. type of energy production avoided by waste-recovered energy.

Three background energy production systems were chosen inthis study. Conversion coefcients to primary energy were deter-mined from Dones et al. (2007) and are presented in Table 1. Thesecoefcients account for energy spent in extraction, rening, provi-sion of fuels, supplementary fuel used for start-up operations andenergy conversion in the energy production plants.

Coal PP and natural gas this background energy system sce-nario assumes electricity production in condensing coal-redplants (average plant in Scandinavia, PP power productiononly) and heat production in decentralized natural gas boilers.

Nordel mix and natural gas this background energy systemscenario assumes electricity production based on the Nordicelectricity mix in 2000 described in Dones et al. (2007), whichcombines the national mixes of Denmark, Norway, Swedenand Finland. Nordel accounts for a mix with shares of non-renewable sources, i.e. fossil and nuclear, and large shares ofrenewable sources such as biomass, hydropower, and wind-solar-geothermal. Heat production is still assumed from decen-tralized natural gas boilers.

Coal CHP with allocation based on energy quality this back-ground energy system scenario assumes both heat and electric-ity is produced in large efcient CHP coal-red power plantswith an efciency of 40% electricity and 45% heat (DEA and

gin aluminium and 60 MJ kg1 for virgin copper production. The

the names chosen for the systems reect the pre-treatment

anaprocess.

MBT Composting mechanical biological treatment with com-posting of the organic ne fraction.

MBT Anaerobic digestion mechanical biological treatmentwith biogas production (dry AD).

MBS Biological drying mechanical biological stabilization orbiodrying MBT.

MT Mechanical pre-treatment mechanical processing beforeenergy recovery.

WtE Mass combustion conventional mass grate combustionprimary energy demand for production of virgin plastic granulateswas calculated based on Hischier (2007). The gure chosen,80 MJ kg1 plastic granulate, reects the average of four types ofvirgin plastic, which are the most commonly used in packagingfound in MSW (i.e. PET, HDPE, LDPE and PP). Primary fuels, suchas hard coal, natural gas and diesel are consumed in the treatmentprocesses and transportation or are avoided by secondary recov-ered products. The primary energy necessary for extraction, ren-ing and provision of these fuels has been calculated based on thereport by Dones et al. (2007).

2.2. Alternative residual waste treatment systems compared

The main difference between the alternative systems investi-gated lays in the type of pre-treatment applied and, therefore,Energinet, 2012). The primary energy (mainly the fuel used) forproduction of electricity and heat is allocated between the twooutputs using the energy quality method described byFruergaard et al. (2009), and are reected in the coefcientsfor this scenario (Table 1).

Daily and seasonal variation in heat demand has been consid-ered and therefore, as a baseline condition, only 70% of producedheat in all CHP scenarios substitutes heat produced in the back-ground energy system.

2.1.4. Primary production of materials and fuelsThe primary energy demand for virgin metals production was

calculated based on data from Classen et al. (2009). The nal g-ures used account 23 MJ kg1 for virgin steel, 194 MJ kg1 for vir-

Table 1Primary energy conversion coefcients.

Energyproduct

Coal PP scenario(MJprimary/MJenergy product)

Nordel 2000 mixscenario (MJprimary/MJenergy product)

Coal CHP energyquality scenario(MJprimary/MJenergyproduct)

Electricity 3.18 2.26 2.43Heat 1.40 1.40 0.28

C. Cimpan, H. Wenzel /Waste Mwithout pre-treatment.

2.2.1. Mass and energy ows within pre-treatmentMass ows were established based on yearly operational data in

three plants described in the sections below. Available analyticdata on inputs and outputs in the same plants was used to estab-lish energy balances related to waste energy content. Process en-ergy consumption gures are based on operation in the specicplants except for MBT Composting and MBT Anaerobic digestionwhich are averages of 7 and respectively 6 German plants(Ketelsen, 2012).2.2.1.1. MBT Composting. The pre-treatment section within thetreatment chain for this alternative is represented by mechanicaland biological processing which takes place in an MBT plant basedon the material stream separation concept (Thiel and Thom-Kozmiensky, 2010). The Ennigerloh MBT plant in Germany, whichwas used to establish mass and energy balances, receives residualor mixed MSW from households (70%) and similar Commercial andInstitutional waste (C&I 30%). The waste from the two sources isprocessed on two lines which merge after initial size reduction andsieving. At this point, the waste has a LHV of 10.8 MJ kg1. A sim-plied process ow diagram with mass and energy balances is pre-sented in Fig. 2a. The outputs from mechanical processing are (1)metal concentrates, (2) two middle caloric (RDF) fractions andone high caloric (SRF) fraction (LHV 1923 MJ kg1), and (3) afraction with low caloric value containing most of the biodegrad-able organic and inert material fractions. The SRF is further nega-tively sorted on NIR machines, i.e. to remove PVC plastics, and issize reduced to 2030 mm in order to be sold as high quality alter-native fuel. The low caloric organic fraction is composted and sta-bilized before being landlled in special cells. The two RDF streamsare sent to dedicated mono-combustion plants while the PVC richresidues are sent to conventional thermal treatment plants. The to-tal end-use energy consumption for pre-treatment was modelledas electricity - 45 kW hel. and natural gas - 41 kW hNG per tonneof processed waste.

2.2.1.2. MBT Anaerobic digestion. Pre-treatment was modelled inthis alternative based on the same composting MBT plant withthe important difference that the organic ne fraction is rst usedfor biogas production and subsequently the digestion residues arestabilized before being landlled. Anaerobic digestion is based onthe study by Ketelsen et al. (2010) and consists of a single stagemesophilic, dry digestion process. Typical biogas yields in Germanplants are between 130 and 150 Nm3 per tonne input to digestionwith a CH4 content of 55%. In this study, the organic ne fractionconstitutes about 40% of the input to pre-treatment, which corre-sponds to a production of 57 Nm3 biogas per tonne input waste(biogas LHV is 19 MJ/Nm3). The total end-use energy consumptionmodelled consists of 65 kW hel. and 58 kW hNG per tonne of pro-cessed waste.

2.2.1.3. MBS Biological drying. Mass and energy ows are based onthe MBS plant located in Osnabrck, Germany, which is treatingresidual waste from households with a LHV of approximately9 MJ kg1. Pre-treatment consists of coarse shredding before thebiological drying process, followed by intensive mechanical pro-cessing (Fig. 2b). For a comprehensive review of process and engi-neering for bioconversion by biological drying please refer to Veliset al. (2009). Biological drying is performed in closed reactors andis optimised to preserve most of the caloric value of degradableorganic matter by controlling the biodegradation process (durationof 7 days). In the mass balance established for this plant, incomingwaste is reduced by approx. 28%, consisting of 25% moisture and3% easily degradable dry matter. The dried waste is mechanicallyprocessed to recover metal concentrates and remove inert materi-als (e.g. stones, glass), which are landlled. The remaining streamconstitutes a high caloric SRF with a LHV of around 15 MJ kg1.Pre-treatment energy use amounts to 100 kW hel. and 25 kW hNGtonne1.

2.2.1.4. MT Mechanical pre-treatment. Mass and energy ows aswell as energy consumption for pre-treatment, in this alternative,is modelled based on operational experience in the large integrated

gement 33 (2013) 16481658 1651waste management facility in Wijster, the Netherlands (describedby Woelders et al. (2011)). Here, residual MSW from households(80%) and similar C&I waste (20%) with a LHV of 10.5 MJ kg1

ana1652 C. Cimpan, H. Wenzel /Waste Mwas mechanically processed on three identical lines in order to re-move high caloric fractions before the remaining stream was fedto the attached WtE plant without further treatment. By the end of2010, one of the three lines was upgraded with additional unit pro-cesses (including NIR sorters) in order to remove plastic fractionsfor recycling from the treated waste. The efciency of this linewas documented by Van Velzen and Jansen (2011). The upgradedline is the basis for pre-treatment used in this study and a simpli-ed process ow diagram is presented in Fig. 2c. The waste re-ceived by the plant comes from municipalities that do not haveseparate collection of plastic packaging waste. The so called postseparation process for plastics performed centrally at the plantis recognised by the Dutch authorities as an alternative and com-plementary to source separation and separate collection. The plas-tic concentrates removed, consisting of hard plastics and a foilplastic concentrate, represent about 8% of the mass fed to this pro-cess line. However they also make up to around 20% of the energycontent in the waste which is then, of course, unavailable for thesubsequent energy recovery. Additionally, the process generatesa high caloric SRF (14 MJ kg1) and a middle caloric RDF(12 MJ kg1) which are also exported for energy recovery. Theremaining mixture, which is fed to conventional WtE, constitutesaround 75% by weight of the initial input and has a LHV just above8 MJ kg1. End-use energy consumption for mechanical processingis 15 kW hel. per tonne waste processed.

2.2.1.5. WtE Mass combustion. This alternative involves no pre-treatment of waste. The waste input was modelled as residual

Fig. 2. Mass and energy ows in pre-treatment: (a) mechanical part of MBT Compostingbefore energy recovery.gement 33 (2013) 16481658MSW with a LHV of 10 MJ kg1, constituting of domestic waste(80%) and similar C&I waste (20%). Bottom ash is processed to re-cover metals and is deposited in a landll (further detailed inSection 2.2.3).

2.2.2. Energy recovery after pre-treatmentTypical new waste incineration plants in Europe, which can be

considered state-of-the-art, have net electrical efciencies be-tween 18% and 24%, mainly depending on their size and boilersteam parameters (Van Berlo and De Waart, 2008). However, thereare several examples of highly advanced WtE plants with signi-cantly higher electrical efciencies (Gohlke and Martin, 2007;Gohlke et al., 2007). These plants employ a range of measures toincrease efciency, such as increased steam parameters, reducedair rate and intermediate reheating, in order to achieve netwaste-to-electricity efciencies of up to 3032%, exemplied bythe WtE plant in Amsterdam. Further increases can be achievedfor example by external superheating in fossil-red boilers (e.g.WtE plants in Mainz and Bilbao), however these options were be-yond the scope of this study.

In northern Europe, heat recovery plays an important role and,WtE plants are usually optimised for combined production of heatand electricity (CHP). CHP production implies a reduction in theamount of electricity that can be produced (i.e. electricity derat-ing). The usual approach to calculating electricity derating is byusing the Carnot factor for heat (Fruergaard et al., 2009; DEA andEnerginet, 2012). However, this approach does not take into con-sideration that state-of-the-art CHP plants, compared to PP plants,

(b) MBS Biological drying and mechanical treatment (c) mechanical treatment (MT)

ation in caloric value such as middle caloric RDF streams. RDFwith a more homogeneous particle size distribution allows for

2.2.2.1. Efciency of combustion-based techniques. WtE plants, both

anaconventional and RDF combustors, were modelled withincreasing efciencies in the two main energy recovery scenar-ios, also for the scenario variations of CHP and PP. Efciencyparameters were settled in the SotA scenario to 18% net electric-ity and 60% heat recovery efciency for CHP and 22% net electri-cal efciency for power only, while in the BAT scenario, this was26% net electricity and 60% heat recovery efciency for CHPproduction and 30% net electrical efciency for power only pro-duction respectively.

Pre-treatment techniques in the rst four alternatives of thestudy produce SRF streams which were modelled co-combustedwith coal in the BAT scenario. Due to the technical challenges ofSRF co-combustion, it is assumed that the average coal-red plantaccepting SRF has lower electricity efciency than the power plantmodelled for the background power production. SRF was assumedco-combusted in a plant with 35% net electricity and 40% heatrecovery efciency in the case of CHP and a maximum 40% netelectricity efciency in the case of power only. Residues from plas-tic sorting and recycling were modelled utilised in cement kilns asalternative fuels, replacing coal on a 1 J:1 J basis.

2.2.2.2. Efciency of biogas utilisation. Biogas is produced in one ofthe alternative treatment chains, MBT Anaerobic digestion. It wasassumed that biogas is combusted in gas engines with generationof heat and electricity. Net electricity efciencies for gas enginesrun between 40% and 48% and total efciencies, with heat genera-tion, between 88% and 96% (DEA and Energinet, 2012). A differenceof 5% electricity efciency was modelled between the two main en-ergy recovery scenarios, with 40% net efciency in the SotA andthe use of uidized bed systems additionally to grate combustionsystems (Friege and Fendel, 2011). However, energy recovery ef-ciency is only marginally improved by the use of RDF compared toraw residual waste, mainly due to limitations to boiler steamparameters, which apply for both types of fuel.

Approximately 800,000 tonnes of SRF were co-combusted incoal-red power plants in 2010 in Germany, 78% of which inbrown or lignite coal-red and 22% in hard coal or black coal-redpower plants. A thorough and updated overview of the situation ofco-combustion of SRF in coal-red power plants in Germany can befound in Thiel and Thome-Kozmiensky (2012). Requirements onSRF quality are higher than for any alternative thermal recoveryoptions (e.g. cement kilns, RDF mono-combustion) and the risk ofsevere technical damage by the use of SRF to modern high-efciency Benson boilers (i.e. supercritical steam state boilers)restricts the use of SRF to older power plants (Friege and Fendel,2011). Maier et al. (2011) reported the average electricity ef-ciency of nine coal-red plants that co-combust SRF at 3536%,which is lower than the state-of-the-art of 4044% for pulverizedcoal-red plants with advanced steam processes.are optimised for high recovery of residual heat, including ue gascondensation in many cases, which allows for both efcient elec-tricity and heat recovery. In this study, electricity derating was ac-counted for by choosing appropriate efciency levels consistentwith state-of-the-art and best available examples of existing WtEplants.

RDF mono-combustion plants are essentially waste incinerationplants built to accommodate feedstock with a high degree of vari-

C. Cimpan, H. Wenzel /Waste M45% in the BAT respectively. Heat recovery was maintained at aconstant value of 40% of thermal energy input for both scenariovariants allowing for heat utilisation.2.2.3. Material recovery technologiesMetal concentrates, both ferrous and non-ferrous, are produced

(1) in the mechanical processing steps of pre-treatment (rst fouralternatives) and (2) in the treatment process of bottom ashes inthe MT and direct WtE alternatives. While in the rst case therecovery of metal concentrates is part of the pre-treatment processin the system (accounting for energy consumption), bottom ashsorting is described separately for the second case. Ferrous andnon-ferrous metal concentrates are assumed recovered in a specia-lised plant and they constitute 9% and 2% respectively of theweight of bottom ash processed (original data from a Danishplant). The energy consumption of 15 kW hel. per tonne bottomash processed was modelled. Lastly, a plastic concentrate is gener-ated in the MT alternative (described in Section 2.2.1.4).

Material concentrates recovered for recycling undergo a seriesof rening, sorting and nal reprocessing steps before exiting thesystem as secondary materials that will substitute primary/virginmaterials on the market. The nal recycling efciency (i.e. quantityof secondary produced materials) is affected by the individual ef-ciency of each processing step (Table 2).

2.2.3.1. Metal recovery and recycling. Analyses of metal concen-trates generated in MBT plants and from bottom ashes after incin-eration show wide variations in actual metal content and metaltype composition (e.g. Gillner et al., 2011; Gosten, 2012). In thisstudy metals content has been conservatively generalised for allalternatives, to 70% in the case of ferrous metals and 50% for NFmetals concentrates. At the same time, for the sake of simplicity,the metal composition is NF metals concentrates has been as-sumed to 70% aluminium and 30% copper.

Ferrous metals concentrates can be sent directly to steel pro-ducers if they comply with the requirements of these industries,however this is usually not the case (Damgaard et al., 2009). Fer-rous metals concentrates separated in MBTs have high contentsof impurities (non-metals), while concentrates from bottom ashesusually do not meet the maximum Cu content requirement. Assuch, ferrous concentrates might undergo an additional reningstep within a metal scrap processing plant, such as a shredder facil-ity, before being sent to a metal smelter. The latter has been as-sumed in this study and energy consumption of 100 MJel. pertonne processed concentrate has been accounted. Non-ferrous con-centrates have to be further rened to remove non-metal residuesand undergo sorting into metal types. This process usually happensin specialised plants that employ heavy media separation. The en-ergy consumption in these facilities is around 300 MJel. per tonneprocessed concentrate (Wens et al., 2010).

Puried metal concentrates are traded on the world market andtherefore production of secondary metals from scrap, at specialisedmetal smelters, was modelled based on generic data from Classenet al. (2009). The cumulated primary energy demand for ferrousmetals reprocessing to steel was calculated to 9 MJ per kg andlosses in the process were assumed at 10% of the scrap input. Alu-minium and copper reprocessing take 24 MJ kg1 and 28 MJ kg1

primary energy respectively and process losses were assumed at16% of input scrap. There are no quality differences between virginor secondary produced metals and therefore a substitution ratio of100% has been used.

2.2.3.2. Plastic recovery and recycling. The composition of plasticconcentrates recovered in the pre-treatment plant (MT alternative)has been analysed by Van Velzen and Jansen (2011), with the plas-tic content being determined at 63%. The rest constituted materialssorted by error in the concentrate such as paper and cardboard.

gement 33 (2013) 16481658 1653The concentrates are sent to plastic sorting plants where the mainplastic types are separated (PET, PE, PP and plastic foil) and a plas-tic mix. Residues and unsorted plastics make up a high caloric SRF

ry mon (

ce

ana(assumed LCV of 20 MJ kg1 due to high shares of paper and card-board) which is used as an alternative fuel in cement kilns. Energyconsumption in the sorting plants is 160220 MJel. per tonne plas-tic concentrate (Bergsma et al., 2011). Subsequently, the separatedhard plastics are processed into regranulate or ake recyclates. Inthe process, remaining contaminants are removed by series ofoperations including washing, drying and extrusion (also to re-move odours). The hard plastic mix and plastic foil are usually trea-ted as lower quality products and are processed to agglomeratewhich is a product mainly recycled/used into structural materialapplications (e.g. benches, roadside poles and sound barriers). Finalreprocessing can occur at a different or at the same plant whichrst sorts the material (latter assumed in this study). A total lossof 25% of plastic materials was estimated for the entire chain (Ta-ble 2), which is also consistent with the ndings of Rigamonti et al.(2009) and Bernstad et al. (2011). The energy consumption in nalreprocessing step was estimated, based on Bergsma et al. (2011), to4 MJel. and 1.1 MJNG for each kg of plastic material processed.

Secondary plastics usually exhibit lower qualities than virginplastics, and therefore it cannot be assumed that they substitutevirgin plastics on a 1:1 basis. Hence, a substitution ratio of 80%has been set, based on a similar thinking as presented byRigamonti et al. (2009).

2.2.4. Collection and transportEnergy consumption for waste collection and transport from

households to the rst pre-treatment facility has been accountedbased on ndings by Larsen et al. (2009). An average value of5 Ldiesel per tonne collected waste and 0.15 Ldiesel tonne1 km1

for a distance of 20 km transport has been used in the model.Transportation between treatment stages was modelled as long-haul truck with a diesel consumption of 0.03 L tonne1 km1. Itwas assumed that metal concentrates, RDF/SRF streams and bot-tom ash to landll are transported for a distance of 100 km, whilesorted metals and plastic concentrates to nal reprocessing plantsare transported for a distance of 500 km.

2.3. Sensitivity analysis

Some key assumptions made in baseline scenarios were tested.

Table 2Efciencies across the material recovery and recycling chain.

Materials Material content inconcentrates (wt%), (A)

Concentrate processing(wt%), (B)

Secondaproducti

Ferrousmetals

70/50a 95 90

NF metals 50 95 84Plastics 63 75b

a Ferrous concentrate recovered during pre-treatment in the MT alternative.b This gure accounts for sorting, washing and re-granulation processes to produ

1654 C. Cimpan, H. Wenzel /Waste MIn the BAT scenarios, generated SRF streams were assumed to beco-combusted in coal-red power plants. It is reasonable to saythat this utilisation option is limited today, and will be further lim-ited in the future, in newly constructed high efciency plants, anddue to decommissioning and long term phase-out of coal-basedenergy. The sensitivity of alternative systems to this energy recov-ery option was assessed by alternatively modelling the use of SRFstreams in RDF dedicated mono-combustion plants and industrialcement production. A simple 1 JSRF:1Jcoal substitution rate was usedin cement kilns. Another important assumption is with regards torecycling of plastics fractions and possibilities to replace virginplastics (in the MT alternative). Different substitution ratios weretested and the effects on this system were assessed and discussed.In a different analysis, it was additionally modelled that residuesfrom plastic sorting and reprocessing are sent to WtE plants in-stead of cement kilns.

3. Results and discussion

The results of the primary energy balance for each alternative,expressed in GJprimary per tonne input waste, are presented in Ta-ble 3, while the nal normalised results, which illustrate primaryenergy savings per unit energy in waste input to systems areshown in Fig. 3. The aim of the normalised result presentation isto eliminate the differences in caloric value of the input wasteows in order to allow consistent comparison of alternatives. Forillustrative reasons the result gures (Fig. 3) are presented per100 MJ waste input to the systems, and are broken down to illus-trate the individual contribution of processes or products. Positivevalues represent induced ows (primary energy consumption),while negative values show avoided ows (primary energy sav-ings) due to substitution of virgin materials and energy in the back-ground systems.

3.1. Overall results

As a general acknowledgment, it was observed that all alterna-tives achieve large primary energy savings, and that these savingsare several times higher than total primary energy consumed tooperate the systems. The magnitude of achieved savings is very dif-ferent in the three background energy systems. The highest net en-ergy savings are gained in the Coal PP background with heatrecovery, which was expected due to the high primary energy costof background end-use energy. The importance of heat recovery isevident, as signicantly lower primary energy substitution isachieved in scenarios without heat recovery.

Transportation needs have a small energy footprint in all sce-narios. Relative to total savings, 34.5% primary energy is spentfor transportation in the Coal PP background with heat recovery,while this increases to a maximum of 59.5% in the Nordel mixbackground without heat recovery. The energy use in pre-treatment plants is a more signicant burden to the systems. Inthis study, pre-treatment by MBS is more energy intensive thanthe other MBTs and is the main expenditure in this system, be-

aterialswt%), (C)

Substitution of primarymaterials (wt%), (D)

Total chain efciency (wt%),(A B C D)

100 60/43a

100 4080 38

nal plastic recyclates.

gement 33 (2013) 16481658tween 9% and 18% relative to total savings. The lowest total processenergy consumption was observed for WtE Mass combustion andthis is attributed almost entirely to transportation needs.

3.2. State-of-the-Art (SotA) efciency scenario

In this technological efciency scenario two treatment alterna-tives stand out by having consistently better performances in allthree background energy systems, namely WtE Mass combustionand MT Mechanical pre-treatment. In background conditions withelectricity production only, and in the Coal CHP background, theMT alternative actually outpaced WtE considerably, displaying1530% more primary energy savings. This is due to the savingsbrought by material recovery (mainly plastics recycling) which

tal primary energy savings (in the combination scenario SotA-

instead of virgin plastics, has not been assessed in the present

anaremain constant in the different backgrounds, thereby making thissystem less vulnerable to changes in background energy systems.

All MBT-based systems showed between 14% and 29% lowerprimary energy savings compared to WtE Mass combustion. Thisis explained by additional energy consumption and losses in wasteenergy content during pre-treatment. Co-combustion of SRFstreams was not included in the SotA scenarios (Section 2.1.2), spe-cically to show the effects when overall efciency is constrainedby RDF/SRF utilisation in conversion techniques with efcienciessimilar to conventional WtE. These results for the SotA scenarioare in agreement with ndings by Consonni et al. (2005a,b), whichwere obtained by using similar system settings with regard to en-ergy recovery. MBT Anaerobic digestion and MBS Biological dryingperform similarly in the SotA scenario, as increased recovery ofelectricity and heat in the MBS alternative is upset by the slightlylarger energy consumption during pre-treatment.

3.3. Best Available Technology (BAT) efciency scenario

For all alternatives, there is a signicant increase in potentialprimary energy savings if the best available technology is usedcompared to standard or state-of-the-art. In scenarios allowingfor heat recovery, BAT energy recovery determined an average in-crease in primary energy savings of 19% in the Coal backgroundand 15% in the Nordel mix compared to SotA. On the other hand,if heat utilisation is not possible, an average increase of more than30% was observed when using BAT instead of SotA. If both avoidedheat and electricity are produced by large Coal CHP plants, theaverage difference between the SotA and BAT scenario was around28%. This indicates that under these background conditions, maxi-mising electricity recovery should be a priority.

Results under the BAT technology scenario show a closer rank-ing distribution, as several alternative treatment systems had sim-ilar net primary energy savings. Under background conditionspermitting heat recovery, the WtE and the MT systems againachieved the highest net savings, but MBS and MBT Anaerobicdigestion came very close, boosted by the high efciency of SRFco-combustion.

If heat utilisation is not possible, again MT indicates possiblegains brought by material recovery over other systems. Increasedelectricity recovery due to SRF co-combustion conditioned MBSBiological drying to achieve the highest savings in the Coal PPbackground and second highest in the Nordel mix. Without heatrecovery, WtE Mass combustion was not able to deliver the samehigh net primary energy savings. SRF co-combustion improvesthe energy prole of MBT Composting, however it does not fullycompensate for the energy content losses during pre-treatment.Production of electricity and heat from recovered biogas more thancompensates for increased energy costs in MBT Anaerobic diges-tion, which had almost the same performance as WtE Mass com-bustion. These results have to be understood in light of thesystem and scenario settings modelled, however, they denote quitewell, in the case of BAT, an almost ideal maximum efciency caseand its implications for energy savings.

3.4. Material recovery

Primary energy savings by substitution of virgin materials ac-counted for a signicant share of total savings in all alternatives.Metals recovery contributed with between 5% and 22% of total pri-mary energy savings in the SotA scenario, and between 4% and 13%of primary energy savings in the BAT scenario. Plastics recyclingcontributed to savings of up to 30% of total savings (in the combi-

C. Cimpan, H. Wenzel /Waste Mnation scenario SotA-Nordel mix-no heat recovery), and down to16% of total savings (in the combination scenario BAT-Coal-withheat recovery). In the MT scenario, material recovery (i.e. metalsstudy. Astrup et al. (2009) show that, in this case, recycling couldpresent no environmental benet, however, if the alternative useof wood is to produce electricity, considerable gains can beachieved by induced energy savings.

4. Limitations and perspectivesNordel mix-no heat). In scenarios where heat recovery was notpossible material recovery became very important. This is furtheraccentuated if the background electricity production has a rela-tively low primary energy demand (i.e. Nordel mix and Coal CHP).

3.5. Sensitivity analysis

With the given assumptions in the baseline scenarios, the per-formance of three systems is very similar: WtE Mass combustion,MT Mechanical pre-treatment and MBS Biological drying. How-ever, primary energy savings in the MT and MBS systems aredependent on assumptions which are somewhat more uncertainthat those of assumptions for direct WtE. The assumptions in ques-tion are (1) SRF co-combustion in coal-red power plants and (2)possibilities regarding plastic recycling.

(1) First, in the BAT scenario, SRF streams were alternatively di-rected to dedicated RDF mono-combustion plants (sensitivity sce-nario BAT no co-combustion/CC). The most noticeable effect was inthe case of MBS. Without SRF co-combustion there is a sharp dropin electricity recovery which, however, is partially compensated byan increase in heat recovery in respective CHP scenarios (examplein Fig. 4 Sensitivity coal PP background with heat recovery). Asonly relatively small streams are co-combusted in the other alter-natives, the difference between the baseline BAT scenario and BATno CC scenario are also smaller. Second, SRF streams were directedto industrial cement kilns both in the BAT and SotA scenarios (sen-sitivity scenarios SotA CK and BAT CK). Consequently, systems pro-ducing SRF streams performed slightly worse in both the Coal andNordel mix backgrounds when CHP was possible. However, if heatrecovery is not possible, or only to a low extent, and also in a CoalCHP background, the alternative use of SRF streams in cement kilnsimproved the performance of the same alternatives compared tobaseline scenarios (Fig. 4 Sensitivity Coal CHP example). In fact,it can be observed that, every alternative performs, in this case,better than direct WtE, in both the SotA and the BAT scenarios.With SRF utilisation in cement kilns, the ash content can be incor-porated into the clinker product and thus substitutes for othermineral raw materials, such as limestone, sands and partly ironore (Thomanetz, 2012). The energy savings from this additionalmaterial substitution have not been added in the calculation mod-el, nevertheless, they are expected to have a marginal contribution.Similarly, bottom ash in all alternatives has been modelled includ-ing transportation to landlls, however, it would be in many casesused as subbase layer in road construction.

(2) Lowering the virgin plastic substitution ratio from 80% to50% conditioned a performance decrease for the MT alternative,this however, did not change its ranking among the best perform-ing systems. This suggests that even when a relatively small part ofrecovered plastics avoid virgin polymers, there are substantial ben-ets. The use of non-recycled plastic sorting residues has to be alsocarefully accounted. Changing the use of plastic residues from ce-ment kilns to WtE had a minor effect on the energy balance. Sub-stitution of other materials, such as wood lumber or concrete,and plastics) and avoided coal accounted for as much as 49% of to-

gement 33 (2013) 16481658 1655The current study demonstrates a number of system dependen-cies and energy implications for residual waste treatment strate-

anaTable 3Primary energy savings due to substitution in GJprimary energy/tonnewaste input.

1656 C. Cimpan, H. Wenzel /Waste Mgies which use mechanical or mechanicalbiological treatment formaterials and before energy recovery, compared with direct ther-mal treatment. The chosen performance indicator, i.e. primary en-ergy balance, is robust to variations and uncertainties of

-84

-99 -95

-115 -115-107

-123 -126-135

-140-150

-100

-50

0

50

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Prim

ary

ener

gy

Coal PP background with heat recovery

-73-84 -84

-102 -98-87

-99 -101

-117-116

-150

-100

-50

0

50

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Nordel mix background with heat recovery

-42-51 -48

-72-59-63

-73-80

-89 -79

-150

-100

-50

0

50

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Coal CHP energy quality background

(MJ

prim

ary

/ 100

MJ

was

te in

put)

Prim

ary

ener

gy(M

J pr

imar

y / 1

00 M

J w

aste

inpu

t)Pr

imar

y en

ergy

(MJ

prim

ary

/ 100

MJ

was

te in

put)

Fig. 3. Primary energy savings

Efciency scenario Energy background MBT Composting MBT Anaerobicdigestion

With heat No heat With heat No h

SotA Coal PP 9.1 5.2 10.6 6.3Nordel mix 7.9 3.7 9.1 4.5Coal CHP 4.6 5.5

BAT Coal PP 11.6 8.7 13.3 9.9Nordel mix 9.4 6.1 10.7 7.0Coal CHP 6.8 7.9gement 33 (2013) 16481658underlying energy and material production systems, however, itis also limited as it of course does not directly reect environmen-tal or socio-economic impacts and other consequences of imple-menting these different strategies.

Material Processing

Pre-treatment

Transport

Electricity Recovery

Heat Recovery

Substituted Coal (cement kilns)

Recycled Metals

Recycled Plastics

Net SotA Scenario

Net BAT Scenario

-49-59 -53

-79-69

-80-92

-105 -102 -94

-150

-100

-50

0

50

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Coal PP background with no heat recovery

-34 -41 -39

-64

-49-57

-65-76 -80 -67

-150

-100

-50

0

50

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

SotA

BAT

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Nordel mix background with no heat recovery

Prim

ary

ener

gy(M

J pr

imar

y / 1

00 M

J w

aste

inpu

t)Pr

imar

y en

ergy

(MJ

prim

ary

/ 100

MJ

was

te in

put)

potential Main results.

MBS Biologicaldrying

MT Mechanical pre-treatment

WtE Masscombustion

eat With heat No heat With heat No heat With heat No heat

8.6 4.8 12.0 8.3 11.5 6.97.5 3.5 10.8 6.7 9.8 4.94.3 7.6 5.911.4 9.5 14.2 10.7 14.0 9.49.1 6.8 12.2 8.4 11.6 6.77.2 9.3 7.9

ry

(BAT no CC) in the Coal PP background scenario with heat recovery and (right side) SRF

anaData from specic plants was used for the modelling of pre-treatment section in compared systems. Although chosen plantswere intended to be representative for the different processingconcepts, there are some limitations in the extent to which the re-sults can be generalised. Except for the composting MBT, waste en-ergy content losses in the other MBT pre-treatment plants werenot large enough to overbalance the gains in energy efciency byuse of more advanced energy recovery routes. For the MBTs basedon the material stream separation concept, biogas production fromthe organic ne fractions was paramount for high energy ef-ciency. In this sense, it is essential for MT and MBT systems, addi-tional to any material recovery, to manage successfully energyows, i.e. concentrate and direct most of the energy in waste to-

Material Processing

Pre-treatment

Transport

Electricity Recove

Heat Recovery

Substituted Coal (cement kilns)

-107-123 -126

-135 -140

-104

-120 -118

-134

-140-150

-100

-50

0

50

BAT

no C

C

BAT

no C

C

BAT

no C

C

BAT

no C

C

BAT

no C

C

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Prim

ary

ener

gySensitivity - Coal PP background with heat recovery

(MJ

prim

ary

/ 100

MJ

was

te in

put)

Fig. 4. Sensitivity analysis (left side) BAT without the possibility of co-combustionutilisation in cement kilns in the Coal CHP background.

C. Cimpan, H. Wenzel /Waste Mwards a form of energy recovery, if an overall high efciency isto be achieved compared to efcient mass combustion WtE. Asan example, energy content losses in the MBT Composting system,modelled here, amounted to around 23% of input (Fig. 2). With SRFco-combustion, this system could not compete with conventionalWtE on an equal footing in the BAT scenario. Yet, SRF use in cementkilns, when WtE CHP is not possible, did condition almost similarenergy savings for the two systems. The results in the presentstudy can be used as a clear indicator that production of high qual-ity SRF alone, with high losses of energy content (in materialstreams disposed), can be insufcient to compete with conven-tional combustion of the entire unprocessed residual waste stream.A clear threshold for an acceptable level of losses is difcult to pin-point, and would be different depending on background conditions(CHP vs. PP) and type of avoided energy production.

Potential primary energy savings by avoiding virgin materialand energy production are relative to the type of assumed energyavoided. From a geographical scope, however, the three chosenbackground systems cover only to a very limited extent the com-plexity of energy systems in Europe. From a temporal scope,assuming that energy recovery from waste substitutes energy pro-duction from fossil sources is still valid in present conditions albeitnot always. Renewable sources are playing an increasing role in theenergy supply. In the future, large shares of energy generated fromuctuating renewable sources like wind and solar will additionallystress the balance between supply and demand, which will mostlikely favour energy technologies with increased production exi-bility, including for energy recovery from waste.Residual municipal waste is hardly storable due to the high con-tent of biodegradable materials and high moisture content, whichreduce its potential for exible use as a fuel. It is additionally char-acterised by variations in composition, particle size distributionand can contain hazardous and problematic substances. Mechani-cal separation and sorting and mechanicalbiological pre-treatment can be used to select, concentrate and prepare wastefractions for diversion towards more advanced material utilisation.From an energy utilisation perspective, waste-derived fuels andbiogas are partially and, respectively, fully storable energy carriers.Future research efforts will include comprehensive environmentalassessment of the role and consequences of sorting and separationsystems for waste in the context of more concrete background con-Recycled Metals

Recycled Plastics

Net Scenario

Net Scenario

-64-73

-102

-78

-59-72

-82

-102-91 -79

-150

-100

-50

0

50

SotA

CK

BAT

CK

SotA

CK

BAT

CK

SotA

CK

BAT

CK

SotA

CK

BAT

CK

SotA

CK

BAT

CK

MBT Composting

MBT Anaerobic digestion

MBS Biological

drying

MT Mechanical

pre-treatment

WtE Mass combustion

Sensitivity - Coal CHP energy quality background

Prim

ary

ener

gy(M

J pr

imar

y / 1

00 M

J w

aste

inpu

t)

gement 33 (2013) 16481658 1657ditions, including future renewable energy systems.

5. Conclusions

In this evaluation, the optimal conditions for residual wastetreatment systems based on conventional thermal WtE were deter-mined largely by opportunities for CHP production, which leads tohigh overall utilisation rates of the energy content in waste. Thesuccess of the three MBT based systems was indeed dependenton the efciency of energy recovery routes after pre-treatment. Areduction in the amount of possible primary energy savings com-pared to mass combustion WtE is unavoidable, due to additionalenergy consumption and process losses, if RDF/SRF is only usedin dedicated WtE plants.

When SRF streams were used in coal-red plants, the energybalance of these systems improved substantially. MBT with anaer-obic digestion and biological drying MBS systems achieved rela-tively similar primary energy savings as efcient CHP masscombustion WtE. In scenarios where CHP production was not pos-sible, as is for example in southern European nations, the biologicaldrying MBS system modelled achieved the highest savings of allsystems, with full stream SRF co-combustion. With heat recoverynot possible, but also if recovered heat was substituting heat fromcoal CHP, SRF utilisation in cement kilns (substituting coal) deter-mined similar (composting MBT) and higher overall energy savings(MBT with anaerobic digestion and biodrying MBS) in systemswith pre-treatment as opposed to conventional WtE.

1658 C. Cimpan, H. Wenzel /Waste ManaPlastic recovery for recycling, by mechanical pre-treatment be-fore energy recovery, supported similar or increased energy sav-ings, in the different scenarios modelled, compared to full streammass combustion. Sensitivity assessment showed overall systemefciency to be robust to different virgin plastic substitution ratios.

Acknowledgements

The authors wish to thank Dr. Bianca Maria Heering (Herhof),Mr. Hans Woelders (Attero) and Mr. Michael Balhar (ASA e.V.) forcontributions with primary data used to establish mass and energyows in pre-treatment plants. Furthermore, we thank the review-ers of this article and our colleague Lorie Hamelin for their con-structive comments and guiding advice.

The nancial support of the 3R Research School, Ama-gerforbrnding, Affaldvarme Aarhus and DONG Energy is grate-fully acknowledged.

References

Arena, U., 2012. Process and technological aspects of municipal solid wastegasication. A review. Waste Manage. 32, 625639.

Astrup, T., Fruergaard, T., Christensen, T.H., 2009. Recycling of plastic: accounting ofgreenhouse gases and global warming contributions. Waste Manage. Res. 27,763772.

Bergsma, G., Bijleveld, M., Otten, M., Krutwagen, B., 2011. LCA: Recycling vankunststof verpakkingsafval uit huishoudens. CE Delft, Delft.

Bernstad, A., La Cour Jansen, J., Aspegren, H., 2011. Life cycle assessment of ahousehold solid waste source separation programme: a Swedish case study.Waste Manage. Res. 29, 10271042.

Christensen, T.H., Simion, F., Tonini, D., Moller, J., 2009. Global warming factorsmodelled for 40 generic municipal waste management scenarios. WasteManage. Res. 27, 871884.

Classen, M., Althaus, H.-J., Blaser, S., Tuchschmid, M., Jungbluth, N., Doka, G., FaistEmmenegger, M., Scharnhorst, W., 2009. Life cycle inventories of metals. FinalReport Ecoinvent Data v2.1, No 10. EMPA Dubendorf, Swiss Centre for Life CycleInventories, Dubendorf, CH.

Consonni, S., Giugliano, M., Grosso, M., 2005a. Alternative strategies for energyrecovery frommunicipal solid waste Part A: Mass and energy balances. WasteManage. 25, 123135.

Consonni, S., Giugliano, M., Grosso, M., 2005b. Alternative strategies for energyrecovery from municipal solid waste Part B: Emission and cost estimates.Waste Manage. 25, 137148.

Consonni, S., Giugliano, M., Grosso, M., Rigamonti, L., 2006. Energy andenvironmental balances of energy recovery from municipal solid waste withand without RDF production. In: Presented at the Venice 2006, Biomass andWaste to Energy Symposium 29 November1 December, CISA, EnvironmentalSanitary Engineering Centre, Italy.

Dahln, L., Vukicevic, S., Meijer, J.-E., Lagerkvist, A., 2007. Comparison of differentcollection systems for sorted household waste in Sweden. Waste Manage. 27,12981305.

Damgaard, A., Larsen, A.W., Christensen, T.H., 2009. Recycling of metals: accountingof greenhouse gases and global warming contributions. Waste Manage. Res. 27,773780.

DEA and Energinet, 2012. Technology Data for Energy Plants: Generation ofElectricity and District Heating Energy Storage and Energy Carrier Generationand Conversion. Danish Energy Agency, Copenhagen, Denmark.

Dones, R., Bauer, C., Bolliger, R., Burger, B., Faist Emmenegger, M., Frischknecht, R.,Heck, T., Jungbluth, N., Roder, A., Tuchschmid, M., 2007. Life cycle inventories ofenergy systems: results for current systems in Switzerland and other UCTECountries. Ecoinvent report No. 5. Paul Scherrer Institut Villigen, Swiss Centrefor Life Cycle Inventories, Dubendorf, CH.

Ekvall, T., Assefa, G., Bjoerklund, A., Eriksson, O., Finnveden, G., 2007. What life-cycleassessment does and does not do in assessments of waste management. WasteManage. 27, 989996.

Friege, H., Fendel, A., 2011. Competition of different methods for recovering energyfrom waste. Waste Manage. Res. 29, 3038.

Fruergaard, T., Astrup, T., Ekvall, T., 2009. Energy use and recovery in wastemanagement and implications for accounting of greenhouse gases and globalwarming contributions. Waste Manage. Res. 27, 724737.

Gillner, R., Wens, B., Schmalbein, N., Pretz, T., 2011. Aspects of the recovery of nf-metals from mixed MSW mechanicalbiological treatment vs. incineration.In: Presented at The 26th International Conference on Solid Waste Technologyand Management, Department of Civil Engineering, Widener University, pp.868878.

Gohlke, O., Martin, J., 2007. Drivers for innovation in waste-to-energy technology.Waste Manage. Res. 25, 214219.Gohlke, O., Seitz, A., Spliethoff, H., 2007. Innovative approaches to increaseefciency in EfW plants potential and limitations. In: Presented at the ISWAAnnual Congress 2007.

Gosten, A., 2012. Metal recycling at waste incineration plants and mechanical wastetreatment plants. In: Thome-Kozmiensky, K.J., Thiel, S. (Eds.), WasteManagement, Recycling and Recovery, vol. 3. TK Verlag Karl Thome-Kozmiensky, Neuruppin, Germany, pp. 361374.

Grosso, M., Motta, A., Rigamonti, L., 2010. Efciency of energy recovery from wasteincineration, in the light of the new Waste Framework Directive. WasteManage. 30, 12381243.

Hischier, R., 2007. Life cycle inventories of packaging and graphical papers.Ecoinvent Report No. 11. Swiss Centre for Life Cycle Inventories. Dubendorf, CH.

Ketelsen, K., 2012. MBTs contribution to climate protection and resourceconservation. In: Presented at the International 9th ASA Recycling Days-MBTas a Supplier of Secondary Raw Materials. Cuvillier Verlag, Goettingen, pp. 1742.

Ketelsen, K., Kanning, K., Cuhls, C., 2010. Optimierung der mechanischbiologischenRestabfallbehandlungsanlagen (MBA) unter Bercksichtigung von Ressourcen-und Klimaschutzaspekten/Optimisation of MBT considering energy efciencyand protection of resources and climate. Federal Environment Agency,Germany.

Koci, V., Trecakova, T., 2011. Mixed municipal waste management in the CzechRepublic from the point of view of the LCA method. Int. J. Life Cycle Assess. 16,113124.

Larsen, A.W., Merrild, H., Mller, J., Christensen, T.H., 2010. Waste collectionsystems for recyclables: an environmental and economic assessment for themunicipality of Aarhus (Denmark). Waste Manage. 30, 744754.

Larsen, A.W., Vrgoc, M., Christensen, T.H., Lieberknecht, P., 2009. Dieselconsumption in waste collection and transport and its environmentalsignicance. Waste Manage. Res. 27, 652659.

Maier, J., Gerhardt, A., Dunnu, G., 2011. Experiences on co-ring solid recoveredfuels in the coal power sector. In: Solid Biofuels for Energy. Green Energy and,Technology, pp. 7594.

Papageorgiou, A., Barton, J.R., Karagiannidis, A., 2009. Assessment of the greenhouseeffect impact of technologies used for energy recovery from municipal waste: acase for England. J. Environ. Manage. 90, 29993012.

Reimann, D.O., 2009. CEWEP Energy Report II (status 20042007): Results ofSpecic Data for Energy, R1 Plant Efciency Factor and Net Caloric Value (NCV)for 231 European WtE Plants. CEWEP, Bamberg, Germany.

Rigamonti, L., Grosso, M., Biganzoli, L., 2012. Environmental assessment ofrefuse-derived fuel co-combustion in a coal-red power plant. J. Ind. Ecol. 16,748760.

Rigamonti, L., Grosso, M., Sunseri, M.C., 2009. Inuence of assumptions aboutselection and recycling efciencies on the LCA of integrated waste managementsystems. Int. J. Life Cycle Assess. 14, 411419.

Thiel, S., Thom-Kozmiensky, K.J., 2010. Mechanicalbiological pre-treatment ofwaste: hope and reality. In: Presented at the ISWA World Congress 2010.Hamburg.

Thiel, S., Thome-Kozmiensky, K., 2012. Co-combustion of solid recovered fuels incoal-red power plants. Waste Manage. Res. 30, 392403.

Thomanetz, E., 2012. Solid recovered fuels in the cement industry with specialrespect to hazardous waste. Waste Manage. Res. 30, 404412.

Tonini, D., Astrup, T., 2012. Life-cycle assessment of a waste renery processfor enzymatic treatment of municipal solid waste. Waste Manage. 32, 165176.

Van Berlo, M.A.J., De Waart, H., 2008. Unleashing the power in waste: comparison ofgreenhouse gas and other performance indicators for waste-to-energy conceptsand landlling. In: Presented at the Proceedings of NAWTEC16, 16th AnnualNorth American Waste-to-Energy Conference May 1921.

Van Velzen, T., Jansen, M., 2011. Nascheiden van kunststofverpakkingsafval teWijster. Wageningen UR Food & Biobased Research, Wageningen.

Velis, C.A., Cooper, J., 2013. Are solid recovered fuels resource-efcient? WasteManage. Res. 31, 113114.

Velis, C.A., Longhurst, P.J., Drew, G.H., Smith, R., Pollard, S.J.T., 2009. Biodrying formechanicalbiological treatment of wastes: a review of process science andengineering. Bioresour. Technol. 100, 27472761.

Velis, C.A., Longhurst, P.J., Drew, G.H., Smith, R., Pollard, S.J.T., 2010. Production andquality assurance of solid recovered fuels using mechanicalbiologicaltreatment (MBT) of waste: a comprehensive assessment. Crit. Rev. Environ.Sci. Technol. 40, 9791105.

Wallmann, R., Fricke, K., Hake, J., 2008. Energieefzienz bei der Mechanischbiologischen Restabfallbehandlung/energy efciency of mechanical biologicaltreatment of residual waste. Mll Abfall 7, 332339.

Wens, B., Gillner, R., Hornsby, K., Pretz, T., 2010. Environmental impacts of NF-metals recycling MSW as a resource. In: Presented at the ISWA WorldCongress 2010, Hamburg.

Woelders, H., Michels, E., Nauts, B., Oosting, M., 2011. Intergrated material andenergy recovery plant Attero (NL). In: Presented at the Sardinia 2011, 13thInternational Waste Management and Landll Symposium 37 October, CISAPublisher.

Zeschmar-Lahl, B., 2010. Waste-to-energy compared to mechanical biologicaltreatment (MBT) and co-combustion of municipal waste. In: Presented at theISWA World Congress 2010, Hamburg.

gement 33 (2013) 16481658

Energy implications of mechanical and mechanicalbiological treatment compared to direct waste-to-energy1 Introduction2 Methodology2.1 Life cycle energy balance2.1.1 System boundaries2.1.2 Efficiency levels of compared technologies2.1.3 Background or primary energy production2.1.4 Primary production of materials and fuels

2.2 Alternative residual waste treatment systems compared2.2.1 Mass and energy flows within pre-treatment2.2.1.1 MBT Composting2.2.1.2 MBT Anaerobic digestion2.2.1.3 MBS Biological drying2.2.1.4 MT Mechanical pre-treatment2.2.1.5 WtE Mass combustion

2.2.2 Energy recovery after pre-treatment2.2.2.1 Efficiency of combustion-based techniques2.2.2.2 Efficiency of biogas utilisation

2.2.3 Material recovery technologies2.2.3.1 Metal recovery and recycling2.2.3.2 Plastic recovery and recycling

2.2.4 Collection and transport

2.3 Sensitivity analysis

3 Results and discussion3.1 Overall results3.2 State-of-the-Art (SotA) efficiency scenario3.3 Best Available Technology (BAT) efficiency scenario3.4 Material recovery3.5 Sensitivity analysis

4 Limitations and perspectives5 ConclusionsAcknowledgementsReferences