In Japan there are about 1200 collective night-soil treatment plants which treat about 42,700,000 population equivalent of night soil and 30,000,000 population equivalent of on-site treatment tank sludge. A sophisticated night-soil treatment system has been developed which uses ultramembrane filtration for the solid-liquid separation stage in a biological denitrification process devised by a joint research and development project between the governmental research institute and a number of private industries.

The effluent from the new system can be anticipated to have levels of BOD, SS, COD, T-N and T-P of about 5 mg/l, 0 mg/l, 35 mg/l, 20 mg/l and less than 0.3 mg/l, respectively. The investment and operational cost of the new system is less than or equivalent to a conventional biological denitrification plant. Furthermore the new system has the advantage of requiring less land and fewer operators. Because of these advantages the new system, i.e. a high-rate biological denitrification process with ultramembrane filtration, is going to be the major system for collective night-soil treatment plants in Japan.

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