Sugarcane Bagasse as a Microbial Host Media for the Passive Treatment of Acid Mine Drainage

Abstract

Anoxic microcosms and flow-through experiments were used to evaluate the ability of sugarcane bagasse to support biogenic sulfide production that can mitigate pH and immobilize heavy metals commonly found in acid mine drainage (AMD). The study was organized in three phases. Phases I and II used mine tailings to generate AMD solutions having a pH near 2, with total metals concentrations in excess of 15 mg/L. Fresh sugarcane bagasse was placed in AMD solutions contained in microcosms at various liquid:solid ratios, under controlled environmental conditions. Within 3 days, significant reductions (>9%) in dissolved As, Cu, Pb, and Zn concentrations were achieved and pH was elevated to circumneutral conditions. Phase III used fresh AMD to challenge flow-through columns packed with bagasse. Reductions in dissolved Cd, Cu, U, and Zn concentrations between 1.5 to 2 orders of magnitude were observed and sustained for more than one year. Column performance was not significantly impacted by temperature fluctuations in the range between 5 and 22°C. Nucleic acid probes confirmed that sulfate reducing bacteria (SRBs) were active and present in the bagasse-containing microcosms. The relative abundance of SRBs suggests they were associated with the sulfide and alkalinity production and that biogenic sulfide was likely responsible for metal removal.