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Cogeneration through the Processing of Domestic Kitchen Waste and Night Soil Sludge in a Full-scale Sludge Treatment Plant
Yutaka Yoneyama*, Katsuhiko Takeno*, Kikuo Shimizu**, Tatsuo Naito**, Fumio Itagaki**, Yoshimitsu Yasuhara** and Mutsuo Nakada***
* Environmental Engineering Group, Ebara Corporation
** Great Joetsu Municipal Zone Association
*** Joetsu Sewage Works Centeriformer member of Great Joetsu Municipal Zone Associationj
õ Correspondence should be addressed to Yutaka Yoneyama:
Environmental Engineering Group, Ebara Corporation
i4-2-1 Honfujisawa, Fujisawa-shi, Kanagawa, 251-8502 Japanj
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 materialinight soil sludge, domestic kitchen wastej, 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 2,243kWh/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.
Key words: methane fermentation, full-scale process, night soil, septic
tank sludge, household kitchen waste