Effect of COD/sulfate ratios on batch anaerobic digestion using waste activated sludge

A study on the effects of the COD/sulfate ratio on characteristics of sulfate-reducing bacteria (SRB) and methane-producing bacteria (MPB), using waste activated sludge (WAS), were performed in batch anaerobic digestion. The methane production rates of untreated and thermal treated WAS were 0.21–1.23, and 0.64–2.02 mL/day VSS, respectively. In the meantime, the hydrogen sulfide gas production rates of untreated and thermal treated WAS were 0–0.36, and 0–0.21 mL/day VSS, respectively. The methane production rate decreased as about 60% at the 11.6 of COD/sulfate ratio. In the case of high influent CODs, the methane production rate increased while the hydrogen sulfide rate decreased. It is thought that it is necessary to regulate the COD concentration in influent wastewaters in order to decrease the effects of SRB. The concentrations of various components such as sulfate should be properly controlled to reduce the methane production inhibition caused by the SRB in the anaerobic digestion using WAS.