Effects of vertical and horizontal configurations of different numbers of brush anodes on performance and electrochemistry of microbial fuel cells

To maximize wastewater treatment and energy production by microbial fuel cells (MFCs), it is important to design the optimal anode arrangement. In this study, four brushes were tested horizontally or vertically to the cathode as the number of the anodes increased from one to four. In the horizontal configuration, adding the anodes greatly reduce electrode resistance and enhanced cell performance, showing four anodes (H4) was the best. In the vertical configuration, two anodes (V2) showed greatest performance and greatest decrease in anode resistance. Compared with one anode, maximum power increased by 59% in H4 and by 18% in V2; anode polarization resistance decreased by 95% in H4 and by 74% in V2; anode impedance decreased by 91% in H2 and by 73% in V2. Cathode resistance was relatively constant, showing adding anodes had negligible effect on it. Because diffusion resistance increases with increasing distance between an anode and a cathode, the vertical anodes should have different diffusion resistance and performances. In this study, adding more anodes vertically decreased cell performance in V3 and V4. However, in a cyclic voltammetry test, current production was substantially increased when the third and the fourth brush anodes were introduced in the both arrangements. Compared with one anode, current production increased by 200% in H4 and by 205% in V4. It shows that the external electrical input relieved diffusion resistance and increased current generation and that installing anodes away from the cathode is a good strategy to increase current production in a system with external power supply such as microbial electrolysis cell. Based on the results, we suggest the following strategy: i) install multiple anodes horizontally along the cathode; ii) install multiple anodes in the second row horizontally along the cathode; iii) install multiple anodes both horizontally and vertically if there is an external power supply.