Abstract
During the anaerobic treatment of sulphate-containing wastewaters, sulphate-reducing bacteria (SRB) compete with methane-producing bacteria (MPB) for the available electron donors. In this work the treatment of a synthetic wastewater, namely, a mixture of acetate, propionate and butyrate with high concentrations of sulphate (COD:sulphate ratio of 0.5–2.5), was studied in upflow anaerobic sludge bed reactors (UASB) operating at 30°C. The influences on the competition between SRB and MPB of two levels of pH (6.75 and 7.75) and low temperature shocks (12–15°C for 3 days) were investigated. The results showed that SRB were able to outcompete MPB at both levels of pH with high (up to 350 mg l−1) and low (below 100 mg l−1) concentrations of free hydrogen sulphide in the digesters. Short-term low temperature shocks had no significant effect on the proportions of feed COD used by SRB and MPB. The COD:sulphate ratio was a key factor affecting the competition between SRB and MPB. At values higher than 0.67 the fraction of degraded COD consumed by SRB decreased, due to sulphate limitation.
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