In this study, electrochemically active microbial biofilms were cultivated and studied at continuously alternating electrode potentials. Compared to cultivation and operation at a single constant potential, this method enhanced microbial turnover and maximum current densities. Electrochemically active microbial biofilms were cultivated in a multi‐carbon source culture for several biofilm generations and were subsequently fed with real, domestic wastewater. Compared to constant potential cultivation, average (N=12) biofilm limiting current density at +0.2 V vs. Ag/AgCl increased from 0.350±0.101 to 0.508±0.099 mA cm−2 with a significant reduction in the time required until the maximum current output was reached from 2.01±0.79 to 1.36±0.71 d. The relative increase in maximum current density and decrease in the time required to reach it are similar. The relative differences of higher over lower values are both approximately 45 %. Biofilm community analysis showed a dominance of Geobacteraceae spp. in the electrochemically active biofilms, which is in accordance with the formal potentials derived from cyclic voltammetry. The overall increase in performance is related to the selection of electrochemically active microorganisms, which exhibit local maxima in their electron transfer kinetics between −0.3 and −0.2 V vs. Ag/AgCl.
This study details, in‐depth, the development of graphite paper as electrodes, specifically anodes, for microbial electrochemical technologies. Processed natural graphite powders were used as an active filler substance in paper composites. Mechanical and electrical properties were balanced during development. Graphite papers with 80 wt% natural graphite content had tear lengths of 730±58 m and resistivities of 0.014±0.001 Ω cm. Electrochemically active biofilms on these materials, cultivated from biomass taken from the bioanodes of an already running bioelectrochemical reactor, were fed with acetate and yielded an average maximum current density of 0.855±0.135 as well as 0.489±0.148 mA cm−2 with a complex substrate mixture. All anodes exhibited similar performance to commonly used carbonaceous electrodes fed the same substrates. This places them as flexible and cheap electrode materials suitable for large‐scale microbial electrochemical technologies.
Whey is a main by‐product of the dairy industry and is difficult to valorise for small and medium enterprises. Microbial electrochemical technologies could be the key for these enterprises to exploit this current waste product. Whey removal and conversion to electrical current was investigated at microbial anodes using potentiostatically controlled half‐cell experiments. The anodes were fed with a whey solution containing ca. 1 g L−1 COD. This can be reliably cleaned with average removal efficiencies of 65.8±10.9 %. The removal coincided with maximum current densities of 0.31±0.06 mA cm−2 and Coulomb efficiencies of 37.1±10.8 %. The anodes are based on a robust complex microbial community. This was established in bioelectrochemical reactors by end of four batch cycles showing an efficient niche differentiation from the following successive enrichments. The microbial analysis revealed a division of labour with mainly planktonic microorganisms degrading the complex whey components by fermentation to organic acids, part of which are subsequently used by the electroactive bacteria at the anode. The results show the need for deciphering microbial structure‐function relationships for future process steering as well as engineering approaches.
The Cover Feature illustrates the complex interconnections and feedback between different groups of parameters during the development of novel graphite paper electrode materials. The featured study shows, in depth, the development of mechanically stable, low resistivity, and good bioelectrochemical performing bioanodes. More information can be found in the Article by D. Y. Alvarez Esquivel et al. on page 1851 in Issue 8, 2020 (DOI: 10.1002/celc.201902087).
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