Improvement of Wastewater Treatment Performance and Power Generation in Microbial Fuel Cells by Enhancing Hydrolysis and Acidogenesis, and by Reducing Internal Losses

Abstract

In this study, biodegradation performance and power generation in MFCs were improved. Domestic wastewater was biodegraded in a dual-chamber MFC system equipped with a DupontTM Nafion® 117 proton exchange membrane, graphite electrodes (8.0 cm × 2.5 cm × 0.2 cm) in both chambers and an external electric circuit with a 100 Ω resistor. Experiments were conducted using an anaerobic inoculum that was prepared onsite by acclimating mixed liquor from municipal wastewater. Aqueous hydrochloric acid (0.1 M HCl, pH 1.82) was used as the electrolyte in the cathode chamber. Free-oxygen conditions were promoted in both chambers by means of a vacuum (77.3 kPa). Low pH (< 5) and mixing conditions were maintained in the anode chamber and all the tests were carried out at 25 ± 1 °C. These conditions enhanced the hydrolysis and acidogenesis, inhibited the methanogenesis and reduced the internal losses. All of them together contributed to improve the treatment performance and power generation of the MFCs. Results of batch tests show COD reductions of up to 95%, voltages peaks of 0.954 V, maximum power densities on the order of 2.1 W·m−2 and 36.9 W·m−3, and energy generation peaks of 99.4 J·mg−1 COD removed. These values are greater than those reported in the MFCs’ literature for municipal wastewater (26 mW·m−2–146 mW·m−2), industrial wastewater (419 mW·m−2) and culture medium solutions (1.17 W·m−2), and similar to those of glucose (3.6 W·m−2). Thus, these results can contribute to further enhancing the energy generated in MFCs and moving forward to make the MFCs more ready for practical applications of bioenergy production.