Waste Management 61 (2017) 1–2
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Life cycle assessment in solid waste management: Facts and artefacts Life cycle assessment or analysis (LCA) has been an area of extensive research in solid waste management (SWM) during the past two decades. The interest in the application of LCA in solid waste management, since 2000, can be viewed in the following graph. As is evident from the graph, the interest on SWM research with LCA increased steadily after 2000 and particularly after 2006. In the last four years, a peak in the number of pertinent publications was observed. In addition, it appears that the preferred term used in publications (articles and reviews) is life cycle assessment rather than life cycle analysis. In addition, the term life cycle inventory, which by definition is one component of a LCA, has gradually reduced in use. Fig. 1 also reveals that between 50% and 60% of the LCA publications in the solid waste field are dedicated to municipal solid waste. During the 90s, LCA started with simple data collection and analysis was done using plain spreadsheets, and sometimes plain paper. Nowadays, complex software packages are used to generate data and to perform analysis. Despite the non-automation of the old approach, scientists focused a lot on what they were doing and knew precisely every detail of their system including boundaries, assumptions, original values, etc. Actually, well known professionals and researchers of LCA in solid waste management, during the first years of its application, simply used ‘‘paper and pencil” to develop their inventories. During the most important part of a LCA, namely the life cycle inventory (LCI), researchers need to obtain and record the direct ‘‘environmental burdens” and the direct ‘‘energy consumption”. The term ‘‘direct” means those environmental emissions and the energy consumption that is associated with the operation of the waste management unit or process under study. In the case of solid waste, researchers are concerned about the environmental burdens (energy consumption can be included under this term) from the moment that a material becomes a waste. The main difference, therefore, from the typical LCA on materials or processes is that the approach of ‘‘cradle to grave” becomes now ‘‘waste to grave”. Original inventory data are important to perform a thorough analysis and a researcher needs to seek those data by performing original research in the laboratory or via field measurements. In addition, meetings and interviews with people in real-scale facilities are required to obtain data especially with regard to water consumption, effluent discharges, electrical energy and diesel consumption, etc. Several times researchers try to fill the gaps using bibliographic data. And this is where the problems appear and LCA starts to be abused. Bibliographic data may have nothing to do with the real operation of the unit (or case) under study.
http://dx.doi.org/10.1016/j.wasman.2017.03.016 0956-053X/Ó 2017 Published by Elsevier Ltd.
As LCA became more popular over the years, several commercial (and occasionally free) LCA ‘‘black box” software, that could allegedly do everything, began to spawn. This is a classic consequence of the commercialization in research. In a similar manner, during the 80s, when groundwater modelling was in fashion, a lot of ‘‘blackbox” groundwater contamination modelling software emerged. Only a few people knew exactly the processes modelled in the software. As a result, many researchers who did not know the basics of groundwater modelling, just plugged in numbers and produced results. The same attitude has unfortunately been practiced with the LCA software that started to emerge during the decade of 2000. Despite the fact that all these software contain important databases and information that have been carefully gathered for years, very few of the users know exactly and in every detail what is contained there and what some terms in the software mean. In addition, as earlier mentioned, those data contained in the databases cannot apply to all cases and cannot cover all real cases. Original data still need to be carefully gathered from scratch and should not be solely based on the data contained in the ‘‘black box” commercial LCA software. It is clear: an incinerator in Denmark might have completely different direct emissions than an incinerator in another part of the world. Based on the experience of one of the authors of this editorial, biowaste composting emissions that were contained in a LCA software were based on emissions from manure composting in the Netherlands. In this case, the results cannot be consistent, and even more, they can be biased to one or another alternative selected for waste management. Therefore, it is essential to validate the original data used in LCA and, if not available, to perform the necessary experimental work to provide reliable input variables; as in any area of applied science. The variation among results from various LCA software that were applied on the same MSW system has been well demonstrated in the important article of Winkler and Bilitewski (2007). Those authors had found variations exceeding 1000% among those results and they pointed out that it is difficult to model MSW systems due to their complexity. In their conclusions, Winkler and Bilitewski (2007) had characteristically noted that ‘‘The variations found in the LCA results of the different models are the result of these difficulties in drawing a real picture within the different modelling approaches. Seen from a very strict perspective of natural science, the degree of variations within the results is too high and not acceptable. Due to the high differences, scientist cannot draw an exact picture of the environmental impacts of a waste management system.” How reliable can, therefore, LCA be for solid waste management? It appears that LCA has a relative value and can only compare
Editorial / Waste Management 61 (2017) 1–2
Number of arcles appearing in Scopus per year
Life Cycle Assessment+SW 70
Life Cycle Assessment + MSW Life Cycle Analysis+SW
Life cycle Analysis + MSW Life Cycle Inventory+SW
50 40 30 20 10 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Fig. 1. Number of publications (articles and reviews) appearing in ScopusÒ that contain the keywords shown in the legend (SW: solid waste, MSW: municipal solid waste) (accessed April 2016).
different scenarios as long as uniform assumptions are strictly maintained over those scenarios. Important components of a LCA are the boundaries of the system and the functional unit as well as several other technical assumptions, such as the inclusion or not of the transportation of an end product and the allocation of the environmental burdens (according to either environmental or economic criteria). Particularly the specification of boundaries is important and this is the aspect that has led to inconsistencies amongst the different studies. The selection of a proper functional unit (FU) is of core importance and can also lead to wrong interpretations if not properly selected. Let us imagine a wastewater biological treatment plant that has operational problems with aeration and does not remove a significant amount of BOD. Probably this plant will not have high environmental impacts during its operation. Would it be fair for this plant, especially when you compare it with a properly operating plant, to render the cubic meter of input wastewater as the FU? The answer is clearly no. We should use the reduction of BOD as a functional unit, or something similar, to obtain fair and reliable conclusions. This is even more critical when managing solid wastes, especially organics. Again, imagine a MBT plant with the main objective to stabilize the organic matter prior to landfilling. Practically all the LCA studies reported in the literature for such plants use weight of the input material as the FU. But again, is this fair (and correct)? Should not be the level of stabilization achieved in the plant be used as the FU? If not, the environmental impacts can be referred to something that is not the real objective of the analysed scenario. The same happens when using compost instead of chemical fertilizers to provide nutrients to crops. The easy way to perform a LCA would have been to use the weight of a nutrient (e.g. N) in each material. But recent studies show that when using compost, there are additional benefits than the simple addition of nutrients (for instance, organic compost has significantly higher antioxidant and anti-carcinogenic properties than chemical fertilizers). In conclusion, LCA is inherently a powerful tool to compare different scenarios or technology alternatives in waste management, when properly used. This proper approach comprises: (i) the use of reliable data, complementing theoretical and experimental and field values, (ii) the proper definition of key points, such as the system boundaries and the functional unit and (iii) a complete sensitivity analysis to be well aware of the consistency of the LCA results. If this is not accomplished, there is no way for LCA to prop-
erly compare scenarios in waste management, which is a typical practice in our field. As someone said years ago: ‘‘Everything should be made as simple as possible, but not simpler." Reference Winkler, J., Bilitewski, B., 2007. Comparative evaluation of life cycle assessment models for solid waste management. Waste Manage. 27, 1021–1031.
Dimitrios Komilis Department of Environmental Engineering, Democritus University of Thrace, Xanthi, Greece E-mail address: [email protected]
Antoni Sánchez Ferrer Universitat Autonoma de Barcelona, Spain E-mail address: [email protected]
Dimitrios Komilis is a faculty of solid waste management at the Department of Environmental Engineering of the Democritus University of Thrace-Greece. His research interests include all aspects of solid waste management and composting.
Antoni Sánchez Ferrer is the head of the compost investigation group in Universitat Autonoma de Barcelona. His current research interests focus on solid state fermentation for the valorisation of organic wastes and the use of nanoparticles in environmental applications. He has more than 130 articles published in indexed journals.