一般廃棄物処理システムの設計における評価と意思決定の支援を志向したLCA手法の適用

Abstract

Background, Aim and Scope. Municipal Solid Waste (MSW) management system has an important role to reduce final disposal of MSW. Recently prevention of global warming in MSW transportation and treatment processes is also coming into important. Decision makers in local region should design the MSW management system that solves above issues, and is desirable for the region in cost constraint. But there are few studies taking into account regional MSW discharge and waste treatment properties and their perspective. In this study, we proposed a methodology to design environmentally and economically desirable MSW management systems in local region by applying Life Cycle Assessment (LCA) and cost analysis.Materials and Methods. The central region of Iwate Prefecture was chosen as a case study. Firstly, we surveyed material and energy inputs/outputs in MSW transportation and treatment processes in the case study area. Then, Life Cycle Inventory (LCI) data of each process was calculated. Secondarily, scenarios involving several MSW management systems considering patterns of MSW treatment technologies and/or MSW segregation were designed. Results and Discussion. As a scenario analysis, Greenhouse Gas (GHG) emissions, SOx/NOx emissions, final disposal and the cost was calculated when each scenario would be for the period from FY2005 to FY2030. From the results, we found that the MSW treatment system in which municipalities form communal MSW treatment mostly has an advantage than the municipality-based MSW treatment system in which municipalities treat MSW by themselves. We also found the trade-off relationship in the results; a system giving priority to gasification and melting facilities decreases the amount of final disposal and cost and increases GHG emissions, while another system giving priority to stoker type grate facility decreases GHG emissions and cost and increases the amount of final disposal. However this trade-off relationship is solved by enhancing waste segregation and/or bio-methanation of kitchen garbage. Additionally, we calculated the indicator value of environmental impact by the Distance-to-target method, and we evaluated a relationship between the indicator value and the cost. As the result, scenario involving the region-based MSW treatment system with bio-methanation is selected as a desirable MSW management system if reduction of final disposal is prioritize as the MSW treatment policy. Conclusions. In the actual fields, it is required not only quantatative evaluation environmental impact and cost but also qualitative investigation such as site selection of waste treatment facilities considering NIMBY phenomenon. Nonetheless, the methodology proposed in this paper is effective for local municipalities’ decision support.