United Utilities

Effect of Sulfate Reduction on Chemical Oxygen Demand Removal in an Anaerobic Baffled Reactor

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Courtesy of United Utilities

Laboratory studies were conducted to investigate the effect of sulfate reduction on chemical oxygen demand (COD) removal in an eight-compartment anaerobic baffled reactor (ABR) at two COD to-sulfate (SO4 2-) ratios (40 [corresponding to 100 mg/L SO4 2-] and 8 [500 mg/L SO4 22]) with an influent COD concentration of 4000 mg/L.The COD was composed of a carbohydrate (sucrose) and protein (peptone) mixture. Sulfate reduction, which had a maximum rate of 0.22 kg SO4 2-/kg volatile suspended solidszd, was primarily confined to the first compartment but was incomplete. It was hypothesized that poor scavenging capacity and sulfate deficiency were responsible. The dissolved sulfide concentrations experienced during this work were less than 130 mg/L (or 4% in gaseous phase) and typically less than the levels expected to cause bacterial inhibition; however, various trophic groups, especially acetogenic bacteria, seemed to be acutely inhibited by hydrogen sulfide (H2S). In contrast, low concentrations of reduced sulfide (15 mg/L H2S(aq)) generated from sulfate reduction stimulated reductive methanogenesis. Nevertheless, overall COD removal decreased with increased sulfate addition and seemed to be influenced by residual COD production. The volatile fatty acid results obtained during this
work were consistent with literature findings, namely, acetate accumulation and lack of acetoclastic activity, improved propionate use, and inert butyrate use.

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