Interaction between acetate fed sulfate reducers and methanogens

During anaerobic treatment of sulfate containing wastewaters, sulfate reducing bacteria (SRB) and methane producing bacteria (MPB) can compete for acetate as the common primary substrate. Since acetate is an intermediate of anaerobic degradation of complex wastes, the outcome of the competition between SRB and MPB can affect the treatment efficiency. The objective of this research was to determine the effects of feed acetate to sulfate ratio and redox potential on the interaction between SRB and MPB. Both batch serum bottles and chemostats were used for this study. The acetate degradation rate constants (k in Monod model), were found to be 2.4 and 3.2/d for SRB and MPB, respectively, and the Monod half velocity coefficients (Ks) were found to be 102 and 116 mg/l for SRB and MPB, respectively. As the feed acetate/SO2−4 ratio was increased from 0.66 to 3.33, the percent acetate utilized by SRB decreased from 71 to only 4% in chemostats and from 40 to 12% in batch serum bottles. The percent acetate utilized by the SRB increased from 19 to 35% when the redox potential was changed from −175 to −75 mV in additional Eh-stat experiments.