The removal of sulfate and metals from mine waters using bacterial sulfate reduction: Pilot plant results

Abstract

A treatment process that bacterially converts sulfate into elemental sulfur via a hydrogen sulfide intermediate was demonstrated at pilot scale for the treatment of three mine waters that contained metals and sulfate. Ethanol served as the bacterial carbon and energy source. The mine waters were treated at rates that ranged from 50–150 L day−1. Contaminant concentrations up to 13 mg L−1 copper, 0.1 mg L−1 mercury, 0.04 mg L−1 cadmium, 3.5 mg L−1 zinc, 0.68 mg L−1 cobalt, 1.3 mg L−1 nickel, 49 mg L−1 iron, and 63 mg L−1 aluminum were removed to meet water quality effluent limits. Manganese removal was about 80% under normal operating conditions but increased to 96% when the process was optimized for manganese removal. The process was shown to be capable of decreasing sulfate concentrations from 1800 mg L−1 to less than 250 mg L−1, nitrate from 100 mg L−1 to less than 1 mg L−1, arsenic from 8 mg L−1 to less than 0.03 mg L−1, and calcium from 310 mg L−1 to less than 100 mg L−1. Acid mine waters were neutralized using bacterially-generated alkalinity; no external alkalinity source was needed.