A sulfate reducing bioreactor controlled by an electrochemical system enables near-zero chemical treatment of metallurgical wastewater

Adaptability of sulfur-disproportionating bacteria for mine water remediation under the pressures of heavy metal ions and high sulfate content

Biological sulfide production processes mediated by sulfate/sulfur reduction have gained attention for metal removal from industrial wastewater (e.g., mine water (MW) and metallurgical wastewater) via forming insoluble metal sulfides. However, these processes often necessitate the addition of external organic compounds as electron donors, which poses a constraint on the broad application of this technology. A recent proof of concept study reported that microbial sulfur disproportionation (SD) produced sulfide with no demand for organics, which could achieve more cost-benefit MW treatment against the above-mentioned processes. However, the resistance of SD bioprocess to different metals and high sulfate content in MW remains mysterious, which may substantially affect the practical applicability of such process. In this study, the sulfur-disproportionating bacteria (SDB)-dominated consortium was enriched from a previously established SD-driven bioreactor, in which Dissulfurimicrobium sp. with a relative abundance of 39.9 % was the predominated SDB. When exposed to the real pretreated acidic MW after the pretreatment process of pH amelioration, the sulfur-disproportionating activity remained active, and metals were effectively removed from the MW. Metal tolerance assays further demonstrated that the consortium had a good tolerance to different metal ions (i.e., Pb2+, Cu2+, Ni2+, Mn2+, Zn2+), especially for Mn2+ with a concentration of approximately 20 mg/L. It suggested the robustness of Dissulfurimicrobium sp. likely due to the presence of genes encoding for the enzymes associated with metal(loid) resistance/uptake. Additionally, although high sulfate content resulted in a slight inhibition on the sulfur-disproportionating activity, the consortium still achieved sulfide production rates of 27.3 mg S/g VSS-d on average under an environmentally relevant sulfate level (i.e., 1100 mg S/L), which is comparable to those reported in sulfate reduction. Taken together, these findings imply that SDB could ensure sustainable MW treatment in a more cost-effective and organic-free way.