Analyse du Cycle de Vie de scénarios de gestion des déchets comprenant du TMB : Analyse des résultats pour la monétarisation | LCA of waste management systems with MBT: Analysis of results for monetization

The European legal framework about solid waste management has been considerably reinforced for more than a decade. One of the most important changes is the EC landfill directive (99/31/EC), which requires the reduction of organic matter in municipal solid waste going to landfill. In an attempt to solve this problem, France has developed for about less than 10 years the Mechanical Biological Treatment (MBT). It is a waste treatment combining on one plant stages of mechanical sorting and biological treatment like composting, stabilisation and anaerobic digestion. Nevertheless, some detractors support the development of a biowaste source-separated collection and its specific treatment. How to compare environmental performances of these MBT scenarios? What weight could be given to the environmental impacts of waste management scenarios, when decision makers consider only market costs as invest and operating costs? Two mean goals are followed. First, we want to highlight the environmental strengths and weaknesses of several waste management scenarios including MBT are highlighted. Then these environmental results are used for a monetization step in order to obtain some individual trade-offs between environmental impacts through an exploratory monetization approach. This paper focuses consequently on the assessment of four residual household solid waste (HSW) management scenarios, which are representative from trends that exist in France: a referential scenario (incineration of residual HSW) and three alternatives that integrate a biological treatment for the organic fraction of the residual HSW. The first alternative is a MBT plant which provides compost through an aerobic degradation of residual HSW. The second alternative is quite similar to the first one but it is built with an additional step of anaerobic degradation, prior to composting, which provides energy recovery from biogas. The third alternative is made up of a source-separated biowaste collection, which is biologically treated in order to produce compost. Remaining HSW are directly burned in an incinerator. Waste management systems studied are limited to residual waste and biowaste flows and take into account collection, transport, treatment, refusal management and by-products valorisation according to the Life Cycle Thinking. Life Cycle Assessment (LCA) is an internationally standardized methodology (ISO 14040 and 14 044) that is considered as one of the most effective environmental management tools. It was chosen to carry out the environmental assessment (Del Borghi et al., 2009). Only three impact categories are presented in this paper: climate change, effects on human health and abiotic resources depletion. A stated preferences method, called Choice Experiment (Hoyos, 2010), and derived from marketing research, is adapted and tested for the monetization of environmental impacts. Through the setting up of an experimental design and survey we have got marginal Willingness to Pay (WTP) for each impact category, which allows trade-offs between these impacts. Judging by our first assessment, environmental impacts results of waste management scenarios with MBT seem to strongly depend on compost spreading process and its fate in agricultural soil, which are the most sensitive steps too, because of their current modelling limits. These results point out a need of a further research concerning knowledge of compost spreading emissions in the fields and they beg the question of the relevance of the organic matter back to soil. Indeed the referential scenario has globally lower impacts than the others, due to the avoided impacts of energy substitution. On the contrary, the second alternative with MBT is the most impacting due to compost spreading. The adaptation of a Choice Experiment (CE) for the monetization of environmental impacts provides certainly WTPs for each impact category mentioned above. These marginal WTPs are sensibly higher for climate change and effects on human health than for abiotic resources depletion. These values are not usable at the moment for several reasons. Firstly, CE is based on individual preferences aggregation. Is it the right scale to weight these environmental impacts? Secondly, the adaptation of this monetization method was tested by bringing additional information on environmental impacts to the respondents and then by taking into accounts the individual level information in the econometric modelling. Further works should be led in this direction to reduce this uncertainty and to set more precisely the adaptation possibilities for environmental impacts.