Low CO<sub>2</sub> footprint remediation of oil-contaminated soil in a sediment microbial fuel cell

Abstract. Active study of electrocatalytic properties of prokaryotes in the last 30 years has led to the creation of a new field of biotechnology – electricity generation in microbial fuel or electrolytic cells, where microbial cells act as biocatalysts of anodic or cathodic processes consuming organic matter or forming biomass and substances with added value during electrotrophic fixation of CO2. The most economically promising is the use of microbial fuel cells (MFC) for wastewater treatment and in bioremediation processes. Recently, the prospects for the introduction of MFC or stimulation of electroactive microbial communities for the purification of oil-contaminated anaerobic layers of soils and marine sediments have been considered. However, this version of the technology has a number of significant technical limitations. We describe a laboratory sedimentary MFC with a bioanode and biocathode inoculated with oil-contaminated soil, which for 210 days of continuous operation was the only source of power supply for an autonomous sensor for monitoring ambient air parameters. Electric current generation in the MFC was accompanied by the destruction of hydrocarbons in contaminated soil and the formation of various microbial populations in the anaerobic soil layer, at the anode and at the cathode, in which potential oil destructors, electrogens and electrotrophs dominated, respectively. At the same time, the release of CO2 against the background of ambient air was minimal, which indicates the formation of an effective gas filter in the MFC. Short-term incubation of the MFC in field conditions revealed a significant effect of temperature fluctuations on the physicochemical parameters of the device, its performance and the composition of the cathode microbial population. We consider in detail the changes in the phylogenetic and physiological diversity of microbial populations of different zones of the sedimentary MFC during its operation, and also outline the prospects and problems of the practical application of such systems for bioremediation of oil-contaminated soil.