Takehiko Ogawa*, Masaharu Tadokoro** and Shigeru Ohno***

* Kanagawa Prefectural Public Health Laboratories
** Kanagawa Prefectural Environmental Research Center
*** Emeritus Professor, Kitasato University

+ Correspondence should be addressed to Takehiko Ogawa:
(52-2, Nakao-cho, Asahi-ku, Yokohama-shi, 241, Japan)

Abstract

Small-scale on-site domestic wastewater treatment systems have recently been used for disposal of domestic wastewater. However, little is known about the quantity and quality of the waste excess sludge discharged from these systems through clearing, because the systems were recently improved.

In this study, the quantity and quality of the excess sludge discharged from the systems were investigated as part of an evaluation of excess sludge treatment at night-soil treatment plants.

The amount of the excess sludge was about 0.84 m3/person/year. Total solid (TS) was 22,000 mg/L, and biological oxygen demand (BOD) was 6,000mg/L. The amount of the excess sludge was 1 - 2.5 times that of the flush toilet wastewater treatment systems and the sludge from the conventional large or middle scale domestic wastewater treatment systems. The concentrations of various sludge components were between that of the sludge from flush toilet systems, and that of the sludge from large- or middle-scale domestic systems. They ranged from 30-70% for the collected night-soil, which contained many solids but little organic matter. These results suggest the necessity for further research on excess sludge treatment systems.

Key words: small-scale on-site domestic wastewater treatment systems, clearing, waste excess sludge, night-soil treatment, sludge treatment