Scaling up 3D-printed urine microbial fuel cells with the membrane electrode assembly

Urine microbial fuel cells (MFCs) show potential for urine treatment to achieve simultaneous organic matter removal and electricity production. However, factors affecting the performance of urine MFCs during scaling up remain unclear. This study develops a 3D-printed air-cathode urine MFC with the membrane electrode assembly (MEA). After scale-up in parallel, unstable anode potential is responsible for the open circuit voltage (OCV) difference among various units, which leads to the energy loss in the system. For systems connected in series, unstable cathode potential mainly contributes to the voltage reversal, resulting in large power loss. Electrochemical impedance spectroscopy analysis indicates dramatically increased ohmic and polarization resistance in both serial and parallel systems. Bode plot further demonstrates after parallel connection, an obvious capacitance effect is observed, which provides evidence to illustrate the phenomenon of non-Faradaic current. Compared to serially connected systems, the capacitor of power management system can harvest more energy from systems connected in parallel. The microbial community analysis demonstrates Geobacter is the most dominant anodic electroactive bacteria both before and after scale-up. Overall, these results show the different strategic improvement should be executed while utilizing parallel connection (focusing on anode) or serial connection (focusing on cathode) to scale up urine MFCs.