Increasing the conductivity of the electrolytes used in microbial electrochemical systems is an essential prerequisite to large‐scale application of these technologies. Microbial anodes formed on carbon felt from a salt marsh inoculum under polarisation at 0.1 V (versus a saturated calomel electrode), generated up to 85 A m−2 in media that contained 30–45 g L−1 of NaCl. Analyses of microbial populations showed a stringent selection of the two microbial genera Marinobacter and Desulfuromonas. Currents decreased if NaCl concentration was increased to 60 g L−1. This highest salinity was shown to consistently impact the bioanode performance in three ways: voltammetry indicated degraded electron‐transfer kinetics, confocal laser scanning microscopy showed a modified biofilm structure and DNA pyrosequencing detected a decrease in the level of Desulfuromonas spp. relative to Marinobacter spp. A consistent correlation was, thus, found between electrochemical kinetics, biofilm structure and the composition of the microbial community.

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The development of economically-efficient microbial electrochemical technologies remains hindered by the low ionic conductivity of the culture media used as the electrolyte. To overcome this drawback, halotolerant bioanodes were designed with salt marsh sediment used as the inoculum in electrolytes containing NaCl at 30 or 45g/L (ionic conductivity 7.0 or 10.4S·m(-1)). The bioanodes were formed at four different potentials -0.4, -0.2, 0.0 and 0.2V/SCE to identify the effect on the electrochemical kinetic parameters, the biofilm structures and the composition of the microbial communities. The bioanodes formed at -0.4V/SCE were largely dominated by Marinobacter spp. Voltammetry showed that they provided higher currents than the other bioanodes in the range of low potentials, but the maximum currents were limited by the poor surface colonization. The bioanodes formed at -0.2, 0.0 and 0.2V/SCE showed similar ratios of Marinobacter and Desulfuromonas spp. and higher values of the maximum current density. The combined analysis of kinetic parameters, biofilm structure and biofilm composition showed that Marinobacter spp., which ensured a higher electron transfer rate, were promising species for the design of halotolerant bioanodes. The challenge is now to overcome its limited surface colonization in the absence of Desulfuromonas spp.

This is the first report to show AR gene dynamics and persistency of potentially pathogenic bacteria through metagenomic approach in cattle manure ambient temperature anaerobic digestion.