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

Abstract

Installment of small-scale on-site domestic wastewater treatment systems has been actively promoted as a part of the waste disposal management plan.

In this study, basic solid-liquid separation characteristics of waste excess sludge from small-scale on-site domestic wastewater treatment systems by cleaning were evaluated for disposal at night-soil treatment plants. The values of various parameters of filtration efficiency in waste excess sludge were far lower than those in digested sludge. Dewaterability from the treatment systems was very poor, and efficient solid-liquid separation was considered to be difficult without sludge conditioning. Characteristics of solid-liquid separation of waste excess sludge from the treatment systems were evaluated experimentally. Mechanical thickening was more effective than gravitational thickening. However, solid-liquid separation was nearly impossible without conditioning of sludge. Dewaterability was markedly improved by conditioning with a polymer coagulant. Methods of sludge dewatering without chemicals were examined for sludge utilization for agriculture and landscape planting. The freezing-thawing process was the most effective, and its conditioning efficiency was comparable to that of chemical coagulation.

Key words: small-scale on-site domestic wastewater treatment systems, waste excess sludge treatment, night-soil treatment, solid-liquid separation, dewaterability