Yasumoto Magara* and Yoshinori Kurosawa**

( *Director, Department of Sanitary Engineering, The Institute of Public Health
**Senior Researcher, Department of Sanitary Engineering, The Institute of Public Health)

Abstract

With about 1,200 collected night soil treatment plants treating about 42,000,000 population equivalent of night soil and 30,000,000 population equivalent of on-site treatment tank sludge. The importance of the collective night soil treatment system to public health as well as ambient water pollution control is very much huge in Japan. Since the development of public sewerage system is very slow, the role of the collected night soil treatment plant should be recognized by citizens. The collected night soil treatment systems has contributed to control of pathogenic diseases including parasitic diseases. The purpose of the collected night soil treatment plant has shifted from pathogen control to ambient water pollution control because Japan has succeeded in managing and controlling pathogenic diseases by the appropriate treatment of night soil and the development of piped water supply systems. Because of strong concensre lated to environmental issues such as the control of environmental carcinogens and the maximum utilization of water resources for national activities, sophisticated night soil treatment technology involving high rate biological denitricication with membrane filtration has been developed through a joint revearch project by govemment and the private sector. Reasons for the success of the new system and also the future target of collective night soil treatment system are discussed in this paper.

Key words: collected night soil treatment, pathogenic disease control, biological denitrification, membrane filtration, cost