Coupled anaerobic/aerobic treatment of high-sulfate wastewater with sulfate reduction and biological sulfide oxidation

A pharmaceutical wastewater with a chemical oxygen demand (COD) concentration of 40,000 mg/l and a sulfate concentration of 5,000 mg/l was treated in a anaerobic baffled reactor. Treatment of the wastewater at 10% dilution was effective but at higher influent concentrations sulfide inhibition reduced efficacy of both COD conversion and sulfate conversion. A recycle line with an attached-film biological reactor was inserted into the anaerobic baffled reactor to facilitate biological sulfide oxidation. Recycling anaerobic effluent through a sulfide oxidizing biological system reduced inhibition in the anaerobic reactor by both reducing inhibitory sulfide concentrations within the reactor and by diluting the influent. The major product of the biological oxidation of sulfide by a Thiobacillus species appeared to be elemental sulfur. At an influent wastewater concentration of 40% and a HRT of 1 day, COD removal efficiencies were greater than 50% and the conversion of influent sulfate was greater than 95% with effluent sulfide concentrations of lees than 20 mg/l. The major product observed from degradation of isopropyl acetate was acetic acid. Coupled anaerobic/aerobic provided removal of sulfur from the wastewater stream and helped to stabilize the pH in the reactor system.