Abstract
A sludge recycling and treatment center that makes use of thermophilic methane fermentation from domestic kitchen waste and night soil sludge started operation in Japan in 2000. The characteristics of the raw material (night soil sludge, domestic kitchen waste), the performance of methane fermentation, the effect of recycle flow on the water treatment system and the cogeneration of electric power has been studied by collecting methane fermentation data for two years. During this period, stable methane fermentation performance was achieved. The highest electrical power generation by methane gas was 2, 243 kWh/day. This was equivalent to about 15.3% of the power consumed at the entire sludge treatment plant. Due to the return water flow from the methane fermentation process, the BOD/Kj-N of the activated sludge influent water was lower compared to when there is no recycle flow. Therefore, there was a tendency for the amount of methanol charged into the secondary denitrification tank to increase. However, the cost of this consumed methanol was small compared to the total running costs. Results indicate that is possible to implement a full-scale treatment plant that makes practical use of organic waste.
