Comparative efficiency of microbial fuel cells and electrocoagulation for the treatment of iron-rich acid mine drainage

Abstract

The present study compares the efficiency of microbial fuel cells (MFCs) and electrocoagulation (EC) for pH increase and Fe removal from Fe-rich acid mine drainage (AMD). The experiments were carried out in batch reactors, using synthetic AMD with initial pH 2.4–2.5 and Fe initial concentration around 500 mg/L. In MFCs, a two-chamber configuration was used (with bioanode using sewage sludge as inoculum, 200–1000 mg/L of sodium acetate as substrate in the anolyte, and AMD as catholyte), separated by an anion exchange membrane (AMI7001). For EC testing, the performance of different electrode materials (Fe and Al), reaction times (15–90 min) and current intensities (100–500 mA) was evaluated. Results showed that MFCs presented the highest efficiency (final pH of 7.7–7.8 and Fe removal >99.9%) at an acetate concentration of 1000 mg/L and corresponding power density between 2 and 20 W/m3. Overall, EC showed the best efficiency with Fe electrodes, at 500 mA and 60 min, yielding a final pH 7.3–7.4 and >94% Fe removal. Thus, both processes seemed to have similar efficiency for the treatment of Fe-rich AMD. However, MFC was found to be about 12 folds more expensive, mostly due to the costs associated to chemical reagents and to membrane replacement after fouling. Finally, the treatment of AMD by MFCs was significantly longer than by EC (days for MFCs vs minutes for EC).