ライフサイクルでの環境面と経済面を考慮した生ごみ再資源化技術評価

Abstract

The environmental impacts and life cycle costs (LCC) of garbage utilization systems were estimated by LCA procedure. Five types of garbage utilization processes were considered: composting; methane fermentation + effluent disposal, methane fermentation + liquid fertilizer, gasification melting and stoker-type incineration.An inventory analysis was carried out to evaluate the environmental loads of each system for construction, processing, and transportation. The environmental impacts were estimated using LIME (Life Cycle Impact Assessment Method based on Endpoint Modeling). The effects of substitution for chemical fertilizer and electric power generation were taken into account in the environmental impact analyses. At the same time, the life cycle cost of each system was calculated using the same functional unit and system boundaries as set in the LCA.Results indicated that the stoker-type incineration system would have the largest environmental impact among the garbage utilization systems considered. The methane fermentation system was more effective in reducing environmental impacts if effluents were used as liquid fertilizer. The effect from saving resource by using liquid fertilizer from the methane fermentation process was significantly large. On the other hand, effects from the electric power generation from incineration or gasification melting systems were negligible. From the point of life cycle costs, construction and collection costs were dominant in all the considered systems. The gasification melting system was estimated to be the most expensive due to its high construction cost. The methane fermentation system was concluded to be the most effective means of garbage utilization for both environmental impacts and life cycle costs.