The performance of microbial anodes in municipal wastewater: Pre-grown multispecies biofilm vs. natural inocula

•Comparison of inoculation strategies for continuously operated microbial anodes.•Inoculation with sludge or plain municipal wastewater yielded similar results.•Also a pre-grown biofilm of exoelectrogens did not yield higher currents .•99% of the pre-grown biofilm was detached after 20 days of operation with wastewater.

In this study, different inoculation strategies for continuously operated microbial anodes are analyzed and compared. After 20 days of operation with municipal wastewater anodes pre-incubated with a biofilm of the exoelectrogenic species Geobacter and Shewanella showed current densities of (65 ± 8) μA/cm2. This is comparable to the current densities of non-inoculated anodes and anodes inoculated with sewage sludge. Analysis of the barcoded pre-grown multispecies biofilms reveal that 99% of the original biofilm was detached after 20 days of operation with municipal wastewater. This is in contrast to previous experiments where a pre-grown biofilm of exoelectrogens was operated in batch mode. To implement pre-grown biofilms in continuous systems it will thus be necessary to reveal a window of process parameters in which typical exoelectrogenic microorganisms including model organisms can be kept and/or enriched on anodes.