Bioelectricity production and bioremediation potential of Withania somnifera in plant microbial fuel cells

Abstract

In p-MFCs living plants photosynthesize within a bio-electrochemical circuit. The plant exudes organic waste material from the roots. In the rhizosphere, bacteria consume these wastes by oxidizing them in contrast to the atmosphere that reduces it. This redox reaction along with photosynthesis can be harnessed as bioelectricity. In this work, the plant Withania somnifera (L.) Dunal was used for generating bioelectricity from the root exudates and organic matter available in the soil. An open circuit voltage of 930±21 mV was achieved between multiple cycles of operation. The cell voltage further increased to 1260±140 mV with enrichment in the form of discards from vegetable matter. The peak recorded voltage was 1400 mV. Graphite fibre felt electrodes ensured uniform microbial growth with power densities that were achieved at 57 mW/m² and 84 mW/m² with and without enrichment respectively. ATR-FTIR demonstrated complete degradation of specific compounds attached to the carbon matrix in the soil along with the polysaccharide content from the enrichments. Additionally, this work also monitored the changes in soil pH and its homogeneity, the impact of photosynthetically active radiation, humidity, and the presence of CO₂ in the air, and how it affects plant growth and ultimately the microbes at the rhizosphere which accounted for the bioremediation and the resultant bioelectricity production. SEM imaging provided additional evidence that the presence of electrochemically active soil bacteria, an anaerobic environment, and electrode characteristics are crucial for the development of conductive biofilms.