PHASE-SEPARATED ANAEROBIC TOXICITY ASSAYS FOR SULFATE AND SULFIDE

As compared with anaerobic toxicity assays (ATA) for industrial toxicants focused only on the acetoclastic methanogens, two phase-separated ATAs for sulfate and sulfide have been conducted by means of acidogenic and methanogenic cultures. Seed sludge was obtained from a two-phase upflow anaerobic sludge blanket (UASB) reactor which operated on glucose as a substrate. The obtained results were compared with those of mixed culture. In the acidogenic ATA, the glucose utilization rate could be expressed in a first-order reaction kinetic. Gas production and substrate utilization were affected slightly when sulfate concentration was up to 6000 mg SO4-S/1. However, the substrate conversion to acetate was retarded by sulfate addition. When sulfide over 800 mgS/1 was added in test bottles, glucose utilization rate was retarded and the first-order kinetic constant decreased. From the results of the methanogenic ATA, it was found that methanogens were more sensitive than acidogens as the sulfate and sulfide concentrations increased. Although methane production was slightly retarded by added sulfate, methane was produced up to 60% of the control when the sulfate was 6000 mg SO4-S/1. Methane production was not inhibited up to 200 mgS/1; however, it was severely retarded at 400 mg S/1. The methane production was completely inhibited in excess of 800 mg S/1. In mixed culture, the inhibiting effects of sulfate and sulfide on mixed culture differed from those of phase-separated anaerobes. Methane production was only slightly inhibited when sulfate and sulfide concentrations reached up to 4000 mg SO4-S/1 and 1200 mg S/1, respectively.