厨芥類の発生抑制と再資源化のトレードオフを考慮した家庭系廃棄物処理のライフサイクル分析

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 1,728 g-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 Alhough 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.