Electrochemical performance of biocathode microbial fuel cells using petroleum-contaminated soil and hot water spring

Microbial fuel cells is growing technology for energy production (electrical and gaseous) with potential electrochemically active bacteria from degradation of unwanted contaminants. Electrogenic [petroleum-contaminated soil (PCS) and hot spring water HSW)] and electrotrophic [activated sludge] bacterial communities were enriched and evaluated for electric current production in biocathode microbial fuel cells (MFC). Molecular phylogenetic (454 pyrosequencing) analysis of environmental samples revealed an overall change in bacterial density and diversity after second-stage enrichment. The predominant electrogenic bacteria grown at anodic biofilms belonged to phylum Proteobacteria (80-98%) in both MFC-1 (PCS) and MFC-2 (HSW) reactors. After enrichment, the major shift in the bacterial species on anodic surface was observed in case of Stenotrophomonas maltophilia (89%) and shewanella sp. (15%) in the respective reactors. Overall, among electrotrophic bacteria, the relative abundance (27-30%) of Pseudomonas aeruginosa was maximum on the cathodic biofilm in both fuel cells. Scanning electron and confocal laser scanning microscopies of biofilms revealed that anode and cathode surfaces were covered with different microcolonies and dispersed bacterial cells. Cyclic voltammetry (-1 to 1V vs. Ag/AgCl) further confirmed the presence of highly proficient electrogenic bacteria capable of generating high electricity ranging from 8mA in MFC-1 and 0.37-Y in MFC-2. Maximum power density of 5500mWm(-2) at a current density of 100mAm(-2) (550)] was recorded in MFC-1 during enrichment stage 2; however, it (P-max=1201mWm(2)) remained 78% lower in MFC-2. Fourier transform infrared spectroscopy and COD removal [86% (SD=8.3 +/- 2.0)] of anolyte (PCS) confirmed active degradation of petroleum contaminants during the operation of MFC-1.