Multi-anode enhanced the bioelectricity generation in air-cathode microbial fuel cells towards energy self-sustaining wastewater treatment.

Microbial fuel cells (MFCs) hold considerable promise for harnessing the substantial energy resources present in wastewater. However, their practical application in wastewater treatment is limited by inadequate removal of organic matter and inefficient power recovery. Previous studies have investigated aeration as a method to enhance the removal of organic matter, but this method is energy-intensive. To address this issue, this study proposed using MFC-recovered bioelectricity for aeration, thereby mitigating the associated expenses. An air-cathode MFC with multi-anode was constructed and optimized to maximize electricity supply for aeration. Carbon-felt anodes were chosen as the most effective anode configuration, due to the high abundance of electroactive bacteria and genes observed in the biofilm generated on their surface. By incorporating six carbon felt anodes, the MFC achieved a 1.7 and 1.1 fold enhancement in the maximum power and current density, respectively. The optimized MFC unit achieved a stable current density of 0.32 A/m2 and achieved COD removal of 60% in the long-term operation of 140 days in a 50 L reactor. In a reactor scaled up to 1600 L, 72 MFCs successfully powered a mini air pump work for 10 s after an 81-s charging period. The intermittent aeration resulted in partial increases in DO concentrations to 0.03-3.5 mg/L, which is expected to promote the removal of nitrogen compounds by the nitrification-anammox process. These groundbreaking results lay the foundation for self-sustaining wastewater treatment technologies.

Long-term evaluation of an air-cathode microbial fuel cell with an anion exchange membrane in a 226L wastewater treatment reactor.

Although the treatment of municipal wastewater using microbial fuel cells (MFCs) has been extensively studied, scaling the systems up for practical use remains challenging. In this study, a 226 L sewage treatment reactor was equipped with 27 MFC units, and its chemical oxygen demand (COD) removal and electricity production were evaluated. The MFC units were tubular air cores with a diameter of 5 cm and length of 100 cm, which were wrapped with a carbon-based cathode, anion exchange membrane (AEM), and nonwoven graphite fabric. The air-cathode-AEM MFC generated 0.12-0.30 A/m2, 0.072-0.51 W/m3, and 1.7-4.6 Wh/m3 in a chemostat reactor with a COD of 140-36 mg/L and hydraulic retention time (HRT) of 9-42 h throughout a year. The decrease in the COD was represented as the first-order rate constant of 0.038. The rate constant was comparable to that of other air-cathode MFCs with cation exchange membranes, indicating the necessity of a posttreatment to meet the discharge standard. It has been estimated that the MFC operation for 24 h before post-aeration can reduce the energy required to meet the discharge standard by 70%, suggesting the potential applicability of MFC in long HRT-treatments such as oxidation ditch. The resistances of the anode, cathode, and AEM were 15, 7.0, and 0.51 mΩ m2, respectively, and surface dirt rather than deterioration primarily increased the AEM resistance. A current exceeding 0.2 A/m2 significantly increases the anode potential, indicating that the current was limited by low COD. Increasing the anode-specific surface area can improve air-AEM MFCs used for practical applications.