Abstract:Cities in China are producing large amounts of municipal solid waste (MSW); however, they have limited MSW treatment capacity, leading to serious environmental problems. MSW recycling systems, such as incineration with energy recovery, landfill gas utilization, and composting, are promising ways to reduce environmental impacts and recover energy and materials. To evaluate MSW recycling systems, we proposed a quantitative eco-efficiency analysis model by integrating life cycle assessment (LCA) and life cycle costing (LCC) analyses. With an effort on consistently combining LCA and LCC, issues about system boundary, allocation, time, aggregation were discussed.Six environmental impact categories, including global warming, ozone layer depletion, acidification, eutrophication, photochemical oxidation and human toxicity, were evaluated and aggregated by LCA. Meanwhile, three cost impact categories, including capital cost, operational cost and disposal costs, were evaluated and aggregated by LCC Environmental and economic impacts of LCA and LCC were normalized and defined as eco-efficiency indicators. We applied the eco-efficiency analysis model to a case in Tianjin, China. We compared three typical MSW recycling scenarios:incineration with energy recovery scenario, landfill with landfill gas utilization scenario, and composting and landfill scenario. We also conducted a contribution analysis for both LCA and LCC to identify critical processes and components leading to environmental impacts and economic costs. Moreover, a sensitivity analysis was performed to investigate the impact of collection and transportation distance on the eco-efficiency indicators. The results show that the composting and landfill scenario is optimum for Tianjin, given the MSW characteristics and technology levels in Tianjin. The LCA results show that the composting and landfill scenario has the lowest environmental impacts, followed by the incineration with energy recovery scenario and landfill with landfill gas utilization scenario. However, the LCC results show that the landfill with landfill gas utilization scenario has the lowest economic impacts, followed by the composting and landfill scenario and incineration with energy recovery scenario. Key components identified by the contribution analysis are global warming for total environmental impacts and capital cost for total economic impacts. Furthermore, emissions of CO2 from MSW incineration process and CH4 from both landfill process and composting process contribute the most to global warming. Photochemical oxidation and human toxicity from the incineration with energy recovery scenario and acidification and eutrophication from both the landfill with landfill gas utilization scenario and composting and landfill scenario contribute significantly to total environmental impact. The sensitivity analysis of collection and transportation distance showed no impact on the rankings of the three scenarios, on the basis of both environmental impacts and economic costs. However, the eco-efficiency indicators showed reversed changes over collection and transportation distance. Considering the practical situation of Tianjin's MSW management, source separation of wet/dry MSW components and composting represent high eco-efficiency and are hence recommended by this study. Given the methodological differences between LCA and LCC, choices and assumptions about their system boundaries, allocation methods, time issues, and aggregation methods should be carefully considered. The eco-efficiency analysis performed in this study is a useful method for supporting MSW recycling systems and sustainable MSW management.