Simultaneous removal of tetrathionate and copper from simulated acidic mining water in bioelectrochemical and electrochemical systems

This study demonstrates (bio)electrochemical tetrathionate (S4O62 −) degradation with simultaneous elemental copper recovery from simulated acidic mining water. The effect of applied external voltage on anodic tetrathionate removal, cathodic copper removal and current density was studied using two-chamber flow-through bioelectrochemical (MEC) and abiotic electrochemical (EC) systems. At low applied cell voltages (≤ 0.5 V), the highest tetrathionate removal rate (150–170 mg L− 1 d− 1) and average current density (15–30 mA m− 2) was obtained with MEC. At applied external voltages above 0.75 V, abiotic EC provided the highest average current density (410–3600 mA m− 2). In bioelectrochemical systems, the current generation likely proceeds via intermediary reaction products (sulfide and/or thiosulfate), while in electrochemical system tetrathionate is oxidized directly on the electrode. The copper removal rates remained low (< 10 mg L− 1 d− 1) in all systems at applied cell voltages below 0.5 V, but increased up to a maximum of 440 mg L− 1 d− 1 in MEC and to 450 mg L− 1 d− 1 in EC at applied cell voltage of 1.5 V. After seven days of operation at applied cell voltage of 1.5 V, copper removal efficiency was 99.9% in both MEC and EC and the average tetrathionate removal rates were 160 mg L− 1 d− 1 and 190 mg L− 1 d− 1, respectively. This study shows that by applying external voltage, tetrathionate and copper can be efficiently removed from acidic waters with bioelectrochemical and electrochemical systems.