2010 Gentil Et Al Models for waste life cycle assessment: Review of technical assumptions

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Models for waste life cycle assessment: Review of technical assumptions
  This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institutionand sharing with colleagues.Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third partywebsites are prohibited.In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further informationregarding Elsevier’s archiving and manuscript policies areencouraged to visit:http://www.elsevier.com/copyright  Author's personal copy Models for waste life cycle assessment: Review of technical assumptions Emmanuel C. Gentil a , Anders Damgaard a , Michael Hauschild b , Göran Finnveden c , Ola Eriksson d ,Susan Thorneloe e , Pervin Ozge Kaplan e , Morton Barlaz f  , Olivier Muller g , Yasuhiro Matsui h , Ryota Ii i ,Thomas H. Christensen a, * a Department of Environmental Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark b DTU Management, Innovation and Sustainability Group, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark c Environmental Strategies Research – fms, Royal Institute of Technology, (KTH) 100 44 Stockholm, Sweden d Department of Technology and Built Environment, University of Gävle, S-801 76 Gävle, Sweden e US EPA, Office of Research and Development, National Risk Management Research Laboratory, 109 T.W. Alexander Drive, Research Triangle Park NC 27711, USA f  Department of Civil, Construction, and Environmental Engineering, NC State University, Raleigh, NC 27695-7908, USA g PricewaterhouseCoopers, 63, rue de Villiers, 92208 Neuilly-sur-Seine, France h Graduate School of Environmental Science, Okayama University, Okayama, Japan i Pacific Consultants Co. Ltd., 1-7-5, Sekito, Tama-shi, Tokyo, Japan a r t i c l e i n f o  Article history: Received 25 February 2010Accepted 3 June 2010Available online 5 July 2010 a b s t r a c t A number of waste life cycle assessment (LCA) models have been gradually developed since the early1990s, in a number of countries, usually independently from each other. Large discrepancies in resultshavebeenobservedamongdifferentwasteLCAmodels,althoughithasalsobeenshownthatresultsfromdifferent LCA studies can be consistent. This paper is an attempt to identify, review and analyse method-ologies and technical assumptions used in various parts of selected waste LCA models. Several criteriawere identified, which could have significant impacts on the results, such as the functional unit, systemboundaries, waste composition andenergymodelling. The modellingassumptions of waste managementprocesses, ranging from collection, transportation, intermediate facilities, recycling, thermal treatment,biological treatment, and landfilling, are obviously critical when comparing waste LCA models.This review infers that some of the differences in waste LCAmodels are inherent to the time they weredeveloped. It is expected that models developed later, benefit from past modelling assumptions andknowledge and issues. Models developed in different countries furthermore rely on geographic specific-ities that have an impact on the results of waste LCA models. The review concludes that more effortshould be employed to harmonise and validate non-geographic assumptions to strengthen waste LCAmodelling.   2010 Elsevier Ltd. All rights reserved. 1. Introduction Since the early 1990s, waste LCA tools have been developed tomodel the environmental performance of waste management sys-tems (Morrissey and Browne, 2004; Björklund et al., 2010). Thesemodels have been developed by a range of environmental protec-tion agencies, universities or consultancies, mainly in Europe andNorthAmerica.However,duetothecomplexnatureofwasteman-agement modelling and the range of country-specific data, thesemodelshavebeendevelopedinrelativeisolationandconsequentlysuffer a lack of harmonisation.LCA can be applied to waste management systems either byusing dedicated waste LCA tools or by using product LCA tools. Inthis paper, the focus is on waste LCA tools for the assessment of an integrated waste management system. It can however be notedthat essentially the same generic LCA methodology can be used ineither case (Finnveden, 1999a; Clift et al., 2000).Winkler (2004) and Winkler and Bilitewski (2007) compared LCA models for waste management, including a quantitativeassessment of six models (ARES, EPIC/CSR, IWM2, MSW-DST, OR-WARE and UMBERTO). The assessment was made by computingthe same waste management scenario (the city of Dresden in Ger-many)inallsixwasteLCAmodels.Discrepanciesofupto1400%forsome results, which lead to contradictory results among models,were identified. The work of  Winkler and Bilitewski (2007) isimportant because the authors were the first to highlight andquantifysignificant differencesamongdifferent wasteLCAmodels.Similarly, Rimaityté et al. (2007) compared the incineration out-puts of the LCA–IWM model with measured emissions data andobserved large differences between the model and the measureddata. Since modelling assumptions, and possibly calculation errors 0956-053X/$ - see front matter   2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.wasman.2010.06.004 *  Corresponding author. Address: Department of Environmental Engineering,Building 115, Technical University of Denmark, DK-2800 Kongens Lyngby,Denmark. Tel.: +45 45251603; fax: +45 45932850. E-mail address:  thc@env.dtu.dk (T.H. Christensen).Waste Management 30 (2010) 2636–2648 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman  Author's personal copy in the models, are leading to different results, it is important toidentify key criteria that could potentially have significant conse-quences on the results of waste LCA models.LCA models are frequently used to compare waste treatmentalternatives (Finnveden and Ekvall, 1998; Björklund and Finnve-den, 2005; Villanueva and Wenzel, 2007). These studies have ingeneral concluded that the relative order of results is consistentamong different studies. In contrast, Winkler and Bilitewski sug-gested that large differences among models resulted in changesin the relative order of treatment and disposal alternatives.Theobjectiveof thispaper is to reviewandanalyseanumberof different LCA models, developed throughout the world, for wasteand recyclables management. The review is based on available lit-erature,consultationwithLCAmodeldevelopersanduseofthedif-ferent models, where possible. The paper focuses on methodology,input parameters and modelling assumptions. For purpose of sim-plification, this paper excludes the life cycle impact assessment(LCIA) phase and does not provide a comparison of inventoriesamong models but rather focuses on the technical assumptionsleading to the results. 2. Waste management and LCA models Waste LCA, as opposed to product LCA, is a system LCA thataims at assessing the environmental performance of a number of interconnected waste management technologies based on a spe-cific waste composition from the point of generation of the wasteto its final disposal. Waste management is defined by all the activ-ities including collection, transport, handling, treatment, materialand energy recovery and disposal of waste, as indicated in Fig. 1.Fig. 1 illustrates a generic waste management system with thelinkagesbetweenthewasteandthewiderenvironment. InawasteLCA, various elements contained in the waste (elemental wastecomposition) are often mathematically linked to the emissionssrcinating from the waste handling, treatments or disposal. Fromagenericperspective,itisexpectedthatawasteLCAmodelhastheability to model the following aspects:   Environmental performance for the management of a variablefractional waste composition. Models should respond to achangeinfractionalwastecomposition, suchasvaryingcontentof e.g. paper and plastic.   Emissions related to the elemental composition of the waste.Models should respond to elemental waste specific emissions,such as, for example, mercury content in newspaper.   Emissions independent of the waste composition. Modelsshouldrespondtowastemanagementprocesses’ operatingspe-cific emissions, such as the amount of dioxin emitted.   Emission offsets with other systems. Models should includesubstitutionwithenergysystemsandmanufacturingofprimaryresources, e.g. such as aluminium.   Flexible system boundaries. Models should be able to includecountry-specific energy mix in the calculation.   Determination of life cycle inventory (LCI) of an integratedwaste management system. Models should include the assess-ment of an integrated and interconnected system composedof number of transportation and waste management processes,ranging from collection to final disposal. 3. Choice of waste LCA tools to be reviewed Almost50LCAmodels arecurrentlyavailableinEurope(EPLCA,2008), and more ona worldwidebasis, withdifferent applicability,functionality,licensingrestrictionsandcosts.Inordertoundertake SocietalOUTPUTSWaste QuantityFractionsElementsproperties Collection BinsBagsBottle banks Transport TrucksShipTrainIndividual vehicles Biological Treatment Compost Anaerobic DigestionMBT Thermal Treatment IncinerationPyrolysisGasification Material Recovery Open-loopClose-loop Landfill Open dumpBioreactor Inert Home CompostingResources and Energy Inputs Construction –Maintenance –Decommission –Ancillary Materials -EnergyDecommission –Ancillary materials –Process related emissions –Waste related emissions Direct Environmental Emissions   Biosphere ForestrySoil Energy System ElectricityHeatFuel Industrial System Reprocessing Carbon sinkIntermediate Facilities  AutomaticManual ExportCo-treatment    S   Y   S   T   E   M    E   X   C   H   A   N   G   E IndirectEnvironmental benefits Fig. 1.  Genericintegratedwastemanagement system. Theouterdottedlinerepresentssocietyat large(earthsystemandtechnosphere). Theinnerdottedlinerepresentsthewaste management systems represented bya number of waste management technologies (light shaded grey). Thedark shadedgrey represents the inputs andthe outputs of the whole waste management system. The boxindicating the systemexchangeshows the relationships of materials and energyflows between the waste industry andwidersociety, through substitution. E.C. Gentil et al./Waste Management 30 (2010) 2636–2648  2637  Author's personal copy a robust review of LCA tools, we evaluated models that fit into thepre-defined selection criteria as listed above.Based on these selection criteria, the following models havebeen considered for the review:   EASEWASTE, Denmark (Kirkeby et al., 2006);   EPIC/CSR, Canada (Haight, 1999, 2004);   IWM2, UK (McDougall et al., 2001);   LCA–IWM, EU (Den Boer et al., 2005a,b, 2007);   MSW-DST, USA (Weitz et al., 1999; Solano et al., 2002a,b; Thor-neloe et al., 2007);   ORWARE, Sweden (Dalemo et al., 1997; Eriksson et al., 2002);   SSWMSS, Japan (Tanaka et al., 2004; Tanaka, 2008);   WISARD, UK (Ecobilan, 1997); and   WRATE, UK (Thomas and McDougall, 2003; Gentil et al., 2005;Coleman, 2006).Other tools, such as ARES (Schwing, 1999), HOLIWAST(HOLIWAST, 2006), LCA-LAND (Nielsen et al., 1998; Nielsen and Hauschild, 1998), MIMES (Sundberg et al., 1994), MSWI (Ciroth, 1998) and WAMPS (Moora et al., 2006) were not included because the availability of the information was either too scarce, the toolonly considered a specific waste management technology, or themodel was not an LCAtool. Asummaryof the development phasesof the different models are presented in Fig. 2. 4. Evaluation approach A set of evaluation criteria has been used to assess the differentLCA models. The main comparison criteria include the functionalunit definition, system boundaries, waste composition, energymix and waste management processes. These criteria are consid-ered of key relevance in waste LCA models (Björklund andBjuggren,1998;Björklund,1998;Eriksson,2003). Otherevaluationcriteria, not covered in this paper, are also of importance, such asopen-loop recycling, multi-loop recycling, cut-off criteria, sensitiv-ity, uncertainty and Monte Carlo analyses. Finally, another veryimportant criterion is the inclusion of comprehensive metadata,critical for understanding the assumptions made for defining thewaste management processes; however, this is also excluded fromthis paper. 4.1. Functional unit  According to ISO 14040 (2006), the functional unit (FU) is thequantified performance of a product or a system for use as a refer-ence unit. The FU is defined in a similar fashion for all the modelsreviewed. The FU generally include all the waste (with a specificcomposition) managed (in tonnes) in a waste management systemoveradefinedtimeperiod(e.g.usually1year),foraspecificregion.The FU canalso be defined by normalisingthe data to one tonne of waste, but this canbeadaptedinall themodels. However, theusershouldbeawareofthesedifferenceswheninterpretingtheLCIandLCIA results. As long as the functional unit is defined consistentlyacrossthemodels,thisshouldnothaveanyinfluenceonthemodelcomparison. 4.2. System boundaries System boundaries are considered to be essential criteria forwasteLCAmodels, sincetheirdefinitioncoulddrasticallyinfluencemodel results (Wenzel and Villanueva, 2006a). In the inventoryanalysis there are three groups of system boundaries (Guinée,2002). Timeconsiderationcanalsobeincludedasa systembound-ary. These types of system boundaries include:   The technical system and the environment;   Time horizon boundaries;   The technical system and other technical systems (upstreamand downstream boundaries, such as the energy system); and   Significantandinsignificantcontributions(boundaryconditionsfor cut-off criteria). 4.2.1. Technical system and the environment  The boundary conditions defined for a waste management sys-temand the environment influencedirectlythe outcomeof anLCAstudy. Waste entering the waste management system as an input,excludes the imbedded inputs because of the technical impossibil-ity to account for all the products’ life cycles ending up as a waste(‘‘Zero’’ burden approach). The level of inclusion and quantity of the inputs and the outputs entering and leaving waste manage-ment systems are different among the different models and canbe different among waste management activities. This is due tothe different complexity and exhaustiveness of the models wheredevelopers had to choose the type and quantity of inputs and out-puts based on best available knowledge at the time of development.The geographical boundaries and therefore the geographicalscope are also critical for the definition of the boundaries betweenthetechnicalsystemandtheenvironmentinwasteLCAmodelling.The reviewed models contain data that are country-specific andthereforeaparticularattentionshouldbetakenwhenusingamod-el developed in one country and used in another. For instance, theenvironmental performance of electricity production could be ModelCountry '94'95'96'97'98'99'00'01'02'03'04'05'06'07'08'09SourceMIMES-wasteSW Sundberg, 1994 ORWARESW Dalemo et al. , 1997, Eriksson et al. , 2002 LCA-LANDDK Nielsen et al. , 1998a,b MSWIGER Ciroth, 1998  ARESGER Schwing, 1999 EPIC/CSRCA Haight, 1999, 2004 MSW-DSTUSA Weitz et al. ,1999, Thorneloe et al  ., 2007 WISARDUK, FR, NZ Ecobilan, 1999 IWM2UK Mc Dougall, 2000 SSWMSS JP Tanaka et al  ., 2004, Tanaka, 2008 LCA IWMEU Den Boer et al. , 2005a,b, 2007 WAMPSSW Moora, et al. , 2006 HOLIWASTEU HOLIWAST, 2006 WRATEUK Gentil et al  , 2005, Coleman, 2006 EASEWASTEDK Kirkeby et al. , 2006 Fig. 2.  Timeline of selected waste LCA models. The grey area indicates the launch time of the models. The solid line represents the active development phase and launch of subsequent versions of the same model, while the dotted line indicates the research leading to the development phase or the subsequent research not necessarily leading toan active development (use of the model as a research tool). This timeline has been developed based on available literature and discussions with authors and developers.2638  E.C. Gentil et al./Waste Management 30 (2010) 2636–2648
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