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

Results of a continuous wastewater experiment conducted in an upflow anaerobic sludge blanket (UASB) reactor at 37 degrees C showed that m- and o-cresois (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 convened by methanogens into methane. (C) 1997 IAWQ. Published by Elsevier Science Ltd.