Evaluation of Environmental Load Mitigation by Overseas Promotion of Decentralised Wastewater Treatment Facilities

Abstract

 We compared the environmental impacts such as waste generation, greenhouse gas emission and water pollution load discharged from various wastewater treatment facilities. The target facilites were septic tanks that are currently widely used abroad, small-scale wastewater treatment systems of which their promotion in the future is expected, overseas adaptable Japanese Johkasou, and centralised sewerage systems. The result suggests that, from the viewpoint of conservation of the water environment, the transition from septic tanks to systems that are able to remove nitrogen is in urgent need. Also, in terms of waste generation mitigation, it is suggested that the overseas adaptation of Japanese Johkasou, which has low sludge discharge volume per removed BOD, appears effective. Difference in greenhouse gas emission volume between centralised systems and decentralised systems decreases as size of treatment facilities becomes smaller. It is showed that when targeted P.E (population equivalent) is lower than 150, decentralised small-scale systems, including the overseas adaptation of Japanese Johkasou, have a lower emission volume than centralised system.

 The effect of reducing environmental impact such as waste generation, greenhouse gas emissions, and water pollution load were compared and examined.