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

Area of Science:

• Environmental Engineering
• Environmental Microbiology
• Geochemistry

Background:

• Mining-influenced water (MIW) poses environmental risks due to acidic pH and high concentrations of metal(loid)s and sulfate.
• Lignocellulosic sulfate-reducing biochemical reactors (SRBRs) offer a passive treatment approach for MIW.
• Steel slag has shown potential for metal(loid) removal and pH neutralization.

Purpose of the Study:

• To design and evaluate a novel two-stage passive treatment system for MIW.
• To assess the efficacy of a steel slag stage followed by an SRBR stage in removing contaminants.
• To investigate the impact of different lignocellulose sources on microbial community development and treatment performance.

Main Methods:

• A two-stage system was developed, combining a basic oxygen furnace slag reactor with SRBRs.
• SRBRs utilized spent brewing grains or sugarcane bagasse as lignocellulose substrates.
• MIW was analyzed for pH, metal(loid)s (Cd, Cu, Zn), and sulfate concentrations before and after treatment.

Main Results:

• The slag stage removed >99% of initial metal(loid)s and increased pH from 2.6 to 12.
• Remixed slag effluent with acidic MIW prior to SRBR treatment mitigated high pH.
• The SRBR stage effectively removed sulfate and additional metal(loid)s, achieving circumneutral pH.
• Cadmium, copper, and zinc removal in SRBRs exceeded 96%, likely via sulfide precipitation.
• Distinct microbial communities, enriched in sulfate-reducing taxa, developed in SRBRs based on lignocellulose source.

Conclusions:

• The integrated two-stage treatment system demonstrates high efficiency in remediating MIW.
• Steel slag and lignocellulosic SRBRs are a viable passive treatment combination for mining sites.
• The choice of lignocellulose source influences microbial community structure in SRBRs.