Sulfide‐Induced Inhibition of Anaerobic Digestion

Batch anaerobic digestion studies of the effects of pH and sulfide concentration upon lactose utilization, acetate utilization, and sulfate reduction using lactate as a carbon source were performed using 100 ml glass syringes. Increased concentrations of un‐ionized $H_{2}S$ inhibited lactose utilization and acetate utilization whereas total sulfide concentration, more than un‐ionized $H_{2}S\text{,}$ inhibited sulfate reduction. Increased retention time was required to carry lactose and acetate utilization to completion in the presence of high concentrations of TS. Almost 90% utilization of lactose at undissociated $H_{2}S$ in excess of 900 mg/L was attained at a retention time of 228 hr. Acetate utilization was 100% complete after 74 days at $175\mathrm{mg}/L‐H_{2}S$ and deteriorated rapidly to zero at higher $H_{2}S$ concentrations. A mechanism is proposed whereby the carbon flow can be diverted from sulfate reduction to methanogenesis in spite of the presence of a high concentration of sulfate.