Anaerobic degradation of benzoate and cresol isomers in sulfate-rich wastewater

Abstract

Results of a continuous wastewater experiment conducted in an upflow anaerobic sludge blanket (UASB) reactor at 37°C showed that m- and o-cresols (225 mg.l-1 each) could be partially degraded, and their presence did not adversely affect methanogenesis of benzoate (1000 mg.l-1) and sulfidogenesis of sulfate (1800-5600 mg.l-1. With 12 hours of hydraulic retention, the reactor on average was able to remove over 99.5% of benzoate, 11.0% of m-cresol, 8.3% of o-cresol and reduce up to 48% of sulfate. Sulfate was reduced at a constant rate of 1630 mg.(l.d)-1, independent of sulfate concentration. Results of batch tests showed that biogranules were able to remove 46.2% of m-cresol and 37.4% of o-cresol in 100 hours. Furthermore, biogranules treating solutions containing 1250 mg.l-1 of sulfate degraded benzoate at an average rate 125% faster than those treating sulfate-free solutions; 74.4% of the electron flow was used for methanogenesis and only 25.6% for sulfidogenesis. Results suggest that most sulfidogens in the biogranule were acetogenic, producing acetate, most of which was subsequently converted by methanogens into methane.