Anoxic sulfide oxidation in wastewater of sewer networks

Investigations on anoxic sulfide oxidation in wastewater under sewer conditions are presented. Batch tests were designed and conducted to study both chemical and biological sulfide oxidation by nitrate in the water phase. Oxidation at pH 7.0 and 8.5 was performed in parallel and wastewater with anaerobic storage period of 0, 3, 4, 6 days was used. Initial sulfide concentrations at a level of 0–4.1 g S m −3 were applied by either addition or sulfate reduction. Results showed that wastewater in sewers was capable of biological, but not chemical, sulfide oxidation under anoxic conditions. Elemental sulfur was the end-product during the experiment. Nitrite accumulates in wastewater as an intermediate. The anoxic oxidation rates for fresh wastewater was 0.48 g S m −3 h −1 at pH 7.0 and 0.62 g S m −3 h −1 at pH 8.5, which accounted for less than 30% of the potential aerobic oxidation rates. A long-term anaerobic adaptation of the wastewater was found to inhibit the oxidation process.