Development of Emissions Factor for the Decentralized Domestic Wastewater Treatment for the National Greenhouse Gas Inventory

摘要

Methane and N₂O emissions were measured simultaneously in three types of decentralized wastewater treatment facilities to develop new emission factors (EFs) in Japan. Considering the ratio of the actual load to designed load and elapsed time from last desludging, 24 sites for Johkasou treating domestic wastewater, 6 sites for Johkasou treating night soil only, and 30 sites for vault toilet were selected. Gas samples were collected in the morning, afternoon, and evening for every Johkasou site. The investigation was conducted in summer and winter to estimate the annual average EFs. The EFs of CH₄ and N₂O of both Johkasou were higher than that used in the national greenhouse gas inventory in 2012, whereas the CH₄ and N₂O EFs of vault toilet were lower. Especially, N₂O EF was only 1% of the national inventory in 2012, and almost zero. According to the results of these three types of decentralized wastewater treatment facilities, the emissions of CO₂eq in FY2010 were 1.77 times higher than the national inventory.