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High Speed and Efficient Methane Fermentation Process for Sewage-Sludge Pretreated Using Sub-Critical Water Technology

Hiroyuki Yoshida, Hayato Tokumoto, Kyoko Nishiguchi, Ryo Ishii, and Takayuki Matubara. Chemical Engineering, Osaka Prefecture University, 1-1 Gakuencho, Sakai, Osaka, Japan

The hydrolysis reaction is considered to be the rate-limiting step in the overall methane fermentation process. After acid formation, methane is produced in 1-3 days. Sub-critical water hydrolysis (Sub-CW) produced various organic acids (mainly acetic acid) at 5-10 min from excess seweage-sludge. When 0.01-0.1 M acetic acid was feeded into the digester, nearly 100% of acetic acid was converted to methane and carbon dioxide in 1-3 days. In Sub-CW hydrolyzed excess sewage-sludge experiment, methane generation rate was 2 times compared to the non-treated excess sewage-sludge after 3 days incubation. In model experiment, mixture of acetic acid and formic acid (mainly composed acetic acid) was completely consumed in 1 day. In addition, almost organic acid was consumed in 1 day. These results suggest that high speed and efficient methane fermentation process is attained using sub-critical water hydrolysis reaction as a pretreatment.