Effects of Aeration and pH on the Performance of Lactic Acid Bacteria-Attached Carbon Fiber Electrode

Abstract

Lactic acid bacteria (LAB) and iron ions dissolved from steelmaking slag (SS), when attached to an electrode surface, improve the performance of carbon fiber electrodes. However, the electrode potential decreases during the attachment (fermentation without aeration), leading to decreased electrode performance when used as a cathode. Additionally, SS dissolution increases the solution pH, which can affect the survival rate of LAB. This study examines the effects of aeration on an electrode potential and solution pH on the survival rate of LAB in solution during fermentation. In the experiments, SS, LAB beverage, bamboo powder, and carbon fiber electrodes were placed in a bottle with and without aeration. Temporal measurements of the solution pH, iron ion concentrations, adenosine triphosphate (ATP), and electrode potential were performed. The results showed that aeration could prevent a 0.5-fold decrease in the electrode potential due to fermentation. The solution pH temporarily increased and exceeded eight during the fermentation, suggesting that SS had been dissolved. ATP began to decrease when the solution pH exceeded 8, indicating that the solution pH influences the survival rate of LAB. It is recommended that the fermentation should be conducted within three days. Furthermore, to improve the performance of a sediment microbial fuel cell (SMFC), the electrodes with and without aeration should be used as the cathode and anode of SMFC, respectively.