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280 Vol.6 No.4 October 2010 1. 背景と目的 現在、食品廃棄物のリサイクルなど廃棄物系バイオマス の利活用が進められており、国内の自治体では厨芥類等の バイオガス化によるエネルギー利用やコンポスト化による 堆肥利用を行う様々なシステムが検討されている。既往の LCA事例1-3)においてもバイオガス化によるエネルギー 利用は従来の焼却処理と比べて厨芥類の水分除去のための エネルギーを必要とせず、また焼却熱による蒸気発電と比 べてガスエンジン発電の効率が高いことから温室効果ガス (GHG)排出量を抑制出来るとされている。 一方、厨芥類には食べ残しなどの食品ロスが含まれる。 日本が食料資源の多くを輸入していることからも食品ロス の発生抑制は重要であり、食品ロス分の生産・流通段階の GHG排出も削減される。しかし、発生抑制された場合は再 資源化量が減り、再資源化によるGHG削減効果が減少する。 このため発生抑制される廃棄物が再資源化されるものか、 焼却されるものかで発生抑制の効果も異なり、その点を含 めた評価も必要である。前述のように再資源化のみを扱っ たLCAの既往研究は多く存在するが、発生抑制とのトレー ドオフを直接扱ったものは国内外で報告されていない。 Synopsis: Objective. The recycling of food waste by biogasification and/or composting is under consideration by some domestic municipalities. At the same time, a reduction in lost food such as leftovers improves self-sufficiency in food and reduces greenhouse-gas (GHG) emissions from the production, distribution and cooking (referred to here as ‘supply’) of the food. But if food loss is reduced, the GHG reduction effect obtained by recycling will be small. In this study, we investigated the amount of food loss in household waste in Kyoto City, and GHG emissions from the supply of the food. On the basis of the results, we conducted a life cycle inventory (LCI) analysis to clarify the trade-off between recycling by biogasification and reduction in food loss. The functional unit is treatment of 218,510t household waste, including lost food, and the supply of the lost food. Results and Discussion. First, this study showed that the amount of food loss is about 20kg/capita/yr. Of this, 8.3kg was directly discarded food and 11.9kg was leftovers. Second, the GHG emissions associated with the supply of this food were estimated. For directly discarded food, it was an average of 1,402g-CO2eq/kg. For leftovers, it was an average of 1,728g-CO2eq/kg. Accordingly, GHG emissions for food loss are about 32kg-CO2eq/capita/yr. LCI analysis revealed that if biogasification were introduced, the elimination of all food loss would cause a decrease in the substitution effect of about 3,000t-CO2eq/yr. But at the same time there would be a decrease of about 46,000t-CO2eq/yr from the production of the lost food. This result shows that a reduction in food loss would be effective even if biogasification were introduced. Conclusions. Although there is some uncertainty in the results, this study shows that a reduction in food loss would be effective and important for GHG reduction. On the basis of the study, we hope that reduction in food loss will be further promoted.

Life Cycle Analysis of Household Waste Management considering Trade-off between Food Waste Reduction and Recycling