Model-Based Evaluation of the Effect of Discharge-Charge on Electric Power Generation of Microbial Fuel Cells

As a method for raising the electric power of microbial fuel cells (MFC), we have noticed that repeat of discharge (closed circuit: CC) and charge (open circuit: OC) produces higher electric power than continuous CC. We tried to find the best interval time for the electric power generation of MFC using compost by experiments and model simulations. As a result of the experiment, the interval time of CC and OC, which was less than 60 seconds, produced about 1.2 times-higher electric power output than the continuous CC. In addition, as for the fixed interval time of CC, which was 30 s, the longer time of OC produced higher power. It is difficult to keep the same condition on the MFC, because each experiment uses the power of the MFC, and then the voltage decreases. Therefore, we simulated the experiments by making a mathematical model for estimating the electric power. The model was based on variation of the concentration of organic compounds, which are consumed by electric current and supplied by diffusion. As a result of the calculation, the effective interval time of CC and OC is less than 15 s. As for the fixed time of CC, the model shows the longer time of OC generates the higher power; however, as the time efficiency, the shorter time of OC is preferable. Therefore, the time efficiency should be considered for practical use of the MFC.