Characteristics and Microbial Community Structural Analysis of Methane Fermentation Sludge for Treating Bean-Curd-Processing Wastewater

The characteristics of methane fermentation for treating bean-curd (tofu)-processing wastewater (BCW) containing waste bean curd frying oil were determined. To facilitate the dispersion and degradation of the oil in the wastewater, lipase and two emulsifiers were adopted. Lipase pretreatment accelerated methane fermentation. Three anaerobic digester series were continuously supplied with BCW and operated under the following conditions: Run 1, without lipase pretreatment, thermophilic methane fermentation (55°C); Run 2, with lipase pretreatment, thermophilic methane fermentation; Run 3, with lipase pretreatment, mesophilic methane fermentation (35°C). Triglycerides and long-chain fatty acids (LCFAs) were completely eliminated by lipase pretreatment in the digester (Runs 2 and 3). The calculation of mass balance demonstrated that 70% of the supplied CODCr in BCW was eliminated in Run 2, and that 60% of the supplied CODCr was converted to methane. However, only 30-40% of the supplied CODCr was converted to methane in Run 3 or 1. The analysis of the microbial community structure in the sludge of the three digesters showed that the sulfate-reducing activity in Run 2 was lower and sulfate-reducing population was also smaller than those in Runs 1 and 3. Lipase pretreatment and thermophilic methane fermentation conditions promote the prevalence of LCFA utilizing hydrogen-producing acetogenic bacteria in the sludge of Run 2.