Microbial fuel cells with polychlorinated biphenyls contaminated soil as electrolyte. Energy performance and decontamination potential in presence of compost

The electrical performance of Terrestrial Microbial Fuel Cells (TMFCs) with soil as the electrolyte was tested with two concentrations (150 or 250 ng/g soil) of PCBs (Polychlorinated biphenlys) and compost (3 % w/w) in an experiment lasting 60 -80 days. Energy output levels were recorded daily by varying the external resistance for detecting the best operating conditions. PCB concentrations and microbiological analyses (total microbial abundance and activity) were performed at the start and end of the experiment. The highest power generation (207 +/- 80 mW/m 2 at 112.5 Omega) was recorded in the presence of compost with the lowest PCB concentration, when compared to TMFCs without compost (1.5 +/- 0.2 mW/m 2 at 300.8 Omega). The results demonstrated that the power generation was correlated with a lower internal resistance and a higher microbial activity. Moreover, chemical results indicated a possible threshold of PCB concentration for the concurrently electricity production and PCB degradation. In fact, PCB removal was obtained only in the cells with high PCB concentration, achieving a reduction of 21 % and 16 % with and without compost, respectively. The microbiological results showed that an additional organic carbon source (methanol or compost) promoted microbial activity and abundance. A positive correlation was found between microbial activity and TMFC electrical output only in the case of PCB low concentration, in the presence of compost. No previous studies addressed the performance of TMFCs with different levels of PCBs in terms of soil decontamination and electricity production. Although a longer experiment is needed, considering PCB persistence in soils, this experiment provided useful information and a new insight on the TMFC effectiveness for soil decontamination and electricity production. The results presented here support considerations about soil resilience through microbial communities and orient further research on contaminant degradation by TMFCs.