Trivalent iron shaped the microbial community structure to enhance the electrochemical performance of microbial fuel cells inoculated with soil and sediment

Bioelectrochemical performance of bacterial communities of cropland soil and lake sediment was evaluated in double chamber microbial fuel cells (MFCs) under the effect of trivalent iron [Fe(III)]. The MFCs were operated in a fed batch mode and their voltage output was measured for a period of 40 days. The highest outputs recorded under untreated conditions using cropland soil and lake sediment were 154 mV (current density= 0.06 mAcm-2, power density = 9.5 mWcm-2) and 137 mV (current density; 0.06 mAcm-2, power density; 7.5 mWcm-2), respectively. An about 87.7% (voltage; 289 mV, power density; 33.4 mWcm-2) and 45% (voltage: 160 mV, current density; 0.06 mAcm-2, power density; 10.24 mWcm-2) increase in voltage output was measured in the respective soil and sediment inoculated MFCs under iron treatment. The COD removal rate increased from 40% and 35-69% and 65% under treated conditions. Alpha rarefaction curves and Shannon index revealed soil derived biofilms contained the most diverse bacterial communities and diversity significantly reduced in sediment biofilm treated with Fe3+. Illumina MiSeq sequencing and scanning electron microscopy indicated the presence of a diverse microbial diversity where Proteobacteria, Bacteriodetes and Firmicutes were the most abundant phyla. Predominant genera included Pseudomonas, Sedimentibacter, Aminobacterium, Clostridium and Flavobacterium sp. MFCs with sediment supported the delta-proteobacteria; the class that includes Shewanella sp. and Geobacter sp., higher in the presence of Fe3+ than soil-MFCs. Based on 16SrRNA sequencing, isolated bacteria were identified as Staphylococcus sp., Bacillus sp., Streptomyces sp. and Gordonia sp., already reported for their electricity generation potential.