2008 Volume 44 Issue 1 Pages 1-9
In small-scale domestic wastewater treatment facilities (Johkasou), it is an important subject to reduce the excess sludge withdrawn from the system, because many of human excrement treatment plants have insufficient capacity for receiving the sludge. In this study, we focused on the performance of aerobic digestion for raw sludge (RS) stored in an inflow tank of Johkasou and a mixture of RS and garbage (GMS) under continuous aeration (CA) and intermittent aeration (IA) conditions. The volume of the reactor was 10 l and the treatment was conducted at 10 days of hydraulic retention time (HRT). The sludge obtained from the mixed liquor in the reactor was separated one to three-days interval by a centrifugal separator and returned to the reactor, and the supernatant was withdrawn as an effluent. After the operation, RS or GMS was fed into the reactors. The MLSS in the reactors increased gradually until around 150 days of the experimental period and kept stable concentrations after then (total experimental period: 229 days). The average sludge decomposition ratios for RS were 72.8％ under CA condition and 67.8％ under IA condition. The average sludge decomposition ratios for GMS were lower than those for RS: 64.7％ under CA condition and 53.3％ under IA condition. In the case of IA condition, both total nitrogen (TN) removals for RS and for GMS were ca. 95％. When RS was treated under CA condition, pH of the effluent decreased to 5.2, but almost complete nitrification was observed.
