Biological Removal of Sulphate from Industrial Effluents and Concomitant Production of Sulphur

Sulphate wastes, such as sulphate-rich industrial effluents or waste gypsum, present a serious environmental pollution problem. A biological sulphate removal process has been evaluated for the treatment of these wastes. In this process, sulphate is converted to H₂S when a carbon source, such as molasses is added. A complete mix reactor was used for sulphate reduction to H₂S, which was subsequently stripped off in a closed system with either CO₂ or nitrogen as carrier gas. The H₂S in turn is oxidized to elemental sulphur in the sulphur production stage when it is brought into contact with a ferric solution. In a subsequent aerobic stage, degradation of organic carbon residuals and calcium carbonate crystallization are achieved simultaneously. Strontium, which is present in waste gypsum, is removed partially in the anaerobic stage, and completely in the aerobic stage. It is shown that sulphate wastes can be treated by the biological sulphate process for the production of reusable water and/or the recovery of valuable by-products such as elemental sulphur, sodium bisulphide and heavy metals.