Life Cycle Assessment of mechanical biological pre-treatment of Municipal Solid Waste: a case study.

The environmental performance of mechanical biological pre-treatment (MBT) of Municipal Solid Waste is quantified using Life Cycle Assessment (LCA), considering one of the 57 French plants currently in operation as a case study. The inventory is mostly based on plant-specific data, extrapolated from on-site measurements regarding mechanical and biological operations (including anaerobic digestion and composting of digestate). The combined treatment of 46,929 tonnes of residual Municipal Solid Waste and 12,158 tonnes of source-sorted biowaste (as treated in 2010 at the plant) generates 24,550 tonnes CO2-eq as an impact on climate change, 69,943kg SO2-eq on terrestrial acidification and 19,929kg NMVOC-eq on photochemical oxidant formation, in a life-cycle perspective. On the contrary MBT induces environmental benefits in terms of fossil resource depletion, human toxicity (carcinogenic) and ecotoxicity. The results firstly highlight the relatively large contribution of some pollutants, such as CH4, emitted at the plant and yet sometimes neglected in the LCA of waste MBT. Moreover this study identifies 4 plant-specific operation conditions which drive the environmental impact potentials induced by MBT: the conditions of degradation of the fermentable fraction, the collection of gaseous flows emitted from biological operations, the abatement of collected pollutants and NOx emissions from biogas combustion. Finally the results underline the relatively large influence of the operations downstream the plant (in particular residuals incineration) on the environmental performance of waste MBT.