Sustainability of Microbial Fuel Cell for Efficient Congo Red Degradation and Energy Recovery Using the Garlic Extract Pretreated Sludge Inoculum

ABSTRACT The main bottleneck found in microbial fuel cells (MFC) is substrate loss due to unwanted microorganisms, which will reduce the electron transfer and hence coulombic efficiency (CE). Methanogens present in the inoculum competitively inhibit the process of electrogenesis, thereby reducing power output. There are various methods established to inhibit the methanogens or to suppress methane production. Among that, the inhibition methods using medicinal plant metabolites are very prevalent. The allicin compound present in garlic extract is reported to inhibit methanogens and hence can be used as a pretreatment agent, which would enhance the performance of MFC. During long‐term operation, to enrich the electrogens to maintain a stable microbial biofilm and suppress the methanogens, unwanted microorganisms in the anodic inoculum should be removed. The combination of extract pretreatment and inoculum removal strategies has been employed in this study to ensure long‐term improved performance. A significant reduction in the methanogenic population of the anaerobic sludge inoculum could be obtained with garlic extract pretreatment. A maximum CE (20%) and maximum power density (8.4 W/m 3 ) could be obtained while using garlic extract pretreated inoculum in MFC. The CE further improved to 31.7% with the removal of sludge inoculum from the MFC. An increase in bio‐electrochemical activity on the anode was observed during cyclic voltammetry and linear sweep voltammetry after the sludge was removed from the system. In addition, the Congo red dye degradation rate was also found to be enhanced using this strategy, which is found to be sustainable.