Boosting voltage generation in dual-chambers microbial fuel cells through multi-parametric optimization of effects of selected factors using Box Behnken design

Abstract

Low electricity output of microbial fuel cells (MFCs) has continued to limit their large-scale applications, as bioenergy sources. Thus effects of surface area of anode (0.005 to 0.015 m2), surface area of cathode (0.005 to 0.015 m2) and volume of substrate in anode chamber (750 to 1500 ml), on MFCs voltage output, were optimized. Replicated Box Behnken Design (Minitab) gave 30 runs. After 25 days operation, average voltage generated by MFCs ranged from 7.76±0.28 mV to 34.32±3.2 mV, across 10 kΩ. Response Optimizer (Minitab) indicated 0.011 m2 as optimal surface area of anode, 0.015 m2 for cathode and 1500 mL for volume of substrate in anode chamber, with estimated maximum voltage of 41.83 mV, when used. This gives 1:1.3:136,363 ratio for surface area of anode, surface area of cathode and volume of substrate in anode, which could be useful in scaling up the device. On application of these optima, highest and lowest average voltages of 54.5±3.2 mV and 20.1±2.7 mV were generated. This maximum voltage was 30.3% higher than the estimate by Response Optimizer, and 58.8% higher than the highest average voltage recorded without optimization. Again, the lowest average voltage (20.13±2.7 mV) obtained after optimization was 159.4% higher than the lowest voltage (7.76±0.28 mV) recorded without optimization. BOD of piggery wastewater, used as substrate, reduced by 18.9%, while COD declined by 31.4%. Diverse Gram-positive and Gram-negative bacterial isolates were identified in the wastewater. Therefore, Box Behnken design is useful optimization of factors, to boost the output of MFCs.