History and Current Situation of Night Soil Treatment Systems and Decentralized Wastewater Treatment Systems in Japan

摘要

In Japan, night soil, or black water, was formerly used as fertilizer for agriculture. However,nduring the rapid economic growth that took place after 1960, chemical fertilizers began to be adopted fornagriculture and night soil was almost abandoned. How to treat the excess of night soil then became a bignchallenge to tackle. From that time a variety of night soil treatment technologies have been developed andnthe Japanese government has actively promoted the construction of night soil treatment facilities all overnthe country. As measures for domestic wastewater treatment, sewerage systems were spread in high-densitynurban areas, while a decentralized system called johkasou was diffused in rural areas with low populationndensity. Johkasou is a unique system that was devised in Japan and mainly treats domestic wastewater onsite.nNight soil treatment systems and decentralized wastewater treatment systems used in Japan arenintroduced in this paper, in the hope that the experience acquired in Japan will contribute to improve thensanitation conditions in other countries.