High Efficacy Two-Stage Metal Treatment Incorporating Basic Oxygen Furnace Slag and Microbiological Sulfate Reduction

Abstract

Lignocellulosic sulfate-reducing biochemical reactors (SRBRs) can be implemented as passive treatment for mining-influenced water (MIW) mitigating the potentially deleterious effects of MIW acidic pH, and high concentrations of metal(loid)s and SO 4 2−. In this study, a novel two-stage treatment for MIW was designed, where basic oxygen furnace slag (slag stage) and microbial SO 4 2− reduction (SRBR stage) were incorporated in series. The SRBRs contained spent brewing grains or sugarcane bagasse as sources of lignocellulose. The slag reactor removed >99% of the metal(loid) concentration present in the MIW (130 ± 40 mg L −1 ) and increased MIW pH from 2.6 ± 0.2 to 12 ± 0.3. The alkaline effluent pH of the slag reactor was mitigated by remixing slag effluent with acidic MIW before SRBR treatment. The SRBR stage removed the bulk of SO 4 2− from MIW, additional metal(loid)s, and yielded a circumneutral effluent pH. Cadmium, copper, and zinc showed high removal rates in SRBRs (≥96%) and likely precipitated as sulfide minerals. The microbial communities developed in SRBRs were enriched in hydrolytic, fermentative, and sulfatereducing taxa. However, the SRBRs developed distinct community compositions due to the different lignocellulose sources employed. Overall, this study underscores the potential of a two-stage treatment employing steel slag and SRBRs for full-scale implementation at mining sites.