ANAEROBIC DEGRADATION OF BENZOATE AND CRESOL ISOMERS IN SULFATE-RICH WASTE-WATER

Results of a continuous wastewater experiment conducted in an upflow a naerobic sludge blanket (UASB) reactor at 37 degrees C showed that m- and o-cresois (225 mg.l(-1) each) could be partially degraded, and the ir 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 remov e over 99.5% of benzoate, 11.0% of m-cresol, 8.3% of o-cresol and redu ce up to 48% of sulfate. Sulfate was reduced at a constant rate of 163 0 mg.(l.d)(-1), independent of sulfate concentration. Results of batch tests showed that biogranules were able to remove 46.2% of m-cresol a nd 37.4% of o-cresol in 100 hours. Furthermore, biogranules treating s olutions containing 1250 mg.l(-1) of sulfate degraded benzoate at an a verage rate 125% faster than those treating sulfate-free solutions; 74 .4% of the electron flow was used for methanogenesis and only 25.6% fo r sulfidogenesis. Results suggest that most sulfidogens in the biogran ule were acetogenic, producing acetate, most of which was subsequently convened by methanogens into methane. (C) 1997 IAWQ. Published by Els evier Science Ltd.