Autotrophic removal of sulphide from industrial wastewaters using oxygen and nitrate as electron acceptors

Abstract

The effect of environmental conditions on sulphide removal was studied in laboratory-scale batch experiments. Sulphide removal was carried out by adding two different electron acceptors (oxygen and nitrate) and stock sulphide solution to activated sludge solutions obtained from a wastewater treatment plant treating molasses-based industrial wastewaters. The effects of pH, temperature, and concentration of activated sludge on specific sulphide oxidation rates were studied. It was found that 80% sulphide removal was achieved when oxygen was used as an electron acceptor with activated sludge, whereas almost 100% sulphide removal was obtained when nitrate was used. Sulphide removal without activated sludge was also determined. The specific sulphide oxidation rate increased approximately 88% with increasing activated sludge concentration with nitrate as an electron acceptor and sulphide was completely removed within 6 min. When oxygen was used as an electron acceptor, specific removal increased up to 92%; however, it was observed that an amount of sulphide remained in the medium, even though the activated sludge concentration was increased. Additionally, the stoichiometry of sulphide oxidation both with nitrate and oxygen were calculated assuming different end products based on thermodynamic approach and compared with experimental yield values.