Life Cycle Assessment of Mechanical-Biological Treatment of Mixed Municipal Waste

The aim of this study is to quantify the environmental exchanges associated with the mechanical-biological treatment (MBT) of mixed municipal waste, for a specific MBT plant, based on the annual operation data for the year 2015. Modeling of environmental performance of the MBT technology is done on actual, real data of the operating plant, taking into account particular, explicit outputs and efficiencies of the plant. Results contribute to quantitative understanding of MBT technology and its environmental impact, including the impacts from individual unit processes within MBT. The study is based on Life Cycle Assessment methodology, employing the EASETECH model. One megagram of mixed municipal waste entering the MBT plant is adopted as the functional unit. The system boundaries cover the whole value chain from collection and transport of mixed municipal waste through mechanical and biological operations until final treatment of end-waste generated in the MBT plant. Results of modeling show the MBT of mixed municipal waste, with accompanying final treatment processes of end-waste has negative impact on the environment. Significant impact categories include photochemical ozone formation, eutrophication, acidification, human toxicity. Aerobic biological treatment of the undersize fraction rich in organic material has the biggest share in total environmental impact, mainly due to ammonia and dinitrogen monoxide emissions. It may suggest that aerobic treatment is not the best option for MBT plants and biogasification with energy recovery can be more beneficial. Landfilling of ballast and stabilized waste, and use of compost for remediation of a closed landfill entail slightly lower environmental impact than the biological treatment. Recycling of secondary materials sorted from residual waste has positive effects on the environment.