Ultrasonic pre-treatment of Bacillus velezensis for improved electrogenic response in a single chambered microbial fuel cell

Abstract

Various microbial strains and techniques are being used to improve power production in microbial fuel cells. Cow dung is a peculiar source of anaerobic and micro-aerophilic organisms that were employed in this study to isolate exo-electrogenic microorganisms. To validate their exo-electrogenic nature, all eight visually distinct bacterial single-cell colonies were tested using the ferrocyanide reduction assay, which resulted in the selection of one bacterial strain AD1-ELB with the ability to reduce ferrocyanide for further biochemical, physiological and electrochemical characterization. The selected strain AD1-ELB was identified as Bacillus velezensis by 16 s rRNA gene sequencing. When used in a single-chambered MFC, the isolated AD1-ELB strain produced a maximum open-circuit voltage of 455 mV with a maximum current density of 51.78 µA/cm2 and maximum power density of 4.33 µW/cm2 on the 16th day. Bacillus velezensis AD1-ELB strain was treated with low-frequency ultrasound (40 kHz) for 1, 2, 3, 4, and 5 min to assess the effect of ultrasonic pre-treatment on an isolated pure culture-based microbial fuel cell. A 3-min exposure to low-frequency ultrasonic therapy resulted in an increase in maximum power of 4.33 µW/cm2 with a current density of 51.78 µA/cm2 in the MFC, which decreases significantly after 4 and 5 min. Thus, the overall power density achieved was 1.89 times greater than in MFCs with untreated strain. These findings support the use of low-frequency ultrasonic stimulation to improve the performance of microbial fuel cell devices and are restricted to the pure, single-cell strain AD1-ELB, with the potential for variation if some other isolated strain is utilized, hence requiring further study to determine its relative variations.