Treatment of Acid Mine Drainage in a Bioelectrochemical System, Based on an Anodic Microbial Sulfate Reduction

Abstract

The possibilities of simultaneous removal of sulfates and heavy metals (Cu, Ni, Zn) from acid mine drainage have been investigated in two-section bioelectrochemical system (BES). The used BES is based on the microbial sulfate reduction (MSR) process in the anode zone and abiotic reduction processes in the cathodic zone. In the present study, the model acid mine drainage with high sulfate (around 4.5 g/l) and heavy metals (Cu 2+ , Ni 2+ and Zn 2+ ) content was performed. As a separator in the laboratory, BES used an anionic exchange membrane (AEM), and for electron donor in the process of microbial sulfate reduction in the bioanode zone -waste ethanol stillage from the distillery industry was employed. In this study, the possibility of sulfates removal from the cathodic zone was established by their forced migration through AEM to the anode zone. Simultaneously, as a result of the MSR process, the sulfate ions passed through AEM are reduced to H 2 S in the anode zone. The produced H 2 S, having its role as a mediator in electron transfer, is oxidized on the anode surface to S 0 and other forms of sulfur. The applicability of waste ethanol stillage as a cheap and affordable organic substrate for the MSR process has also been established. Heavy metals (Cu 2+ , Ni 2+ and Zn 2+ ) occur in the cathode chamber of BES in different degrees of the removal. As a microbial fuel cell (MFC) operating for 120 hours, the reduction rate of Cu 2+ reaches 94.6% (in waste ethanol stillage) and 98.6% (in the case of Postgate culture medium). On the other hand, in terms of Ni 2+ and Zn 2+ , no significant decrease in their concentrations in the liquid phase is found. In the case of microbial electrolysis cell (MEC) mode reduction of Cu 2+ -99.9%, Ni 2+ -65.9% and Zn 2+ -64.0% was achieved. For 96 hours, the removal of sulfates in MEC mode reached 69.9% in comparison with MFC mode -35.2%.