AUTHOR=Jourdin Ludovic , Raes Sanne M. T. , Buisman Cees J. N. , Strik David P. B. T. B. TITLE=Critical Biofilm Growth throughout Unmodified Carbon Felts Allows Continuous Bioelectrochemical Chain Elongation from CO2 up to Caproate at High Current Density JOURNAL=Frontiers in Energy Research VOLUME=6 YEAR=2018 URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2018.00007 DOI=10.3389/fenrg.2018.00007 ISSN=2296-598X ABSTRACT=

Current challenges for microbial electrosynthesis include the production of higher value chemicals than acetate, at high rates, using cheap electrode materials. We demonstrate here the continuous, biofilm-driven production of acetate (C2), n-butyrate (nC4), and n-caproate (nC6) from sole CO2 on unmodified carbon felt electrodes. No other organics were detected. This is the first quantified continuous demonstration of n-caproate production from CO2 using an electrode as sole electron donor. During continuous nutrients supply mode, a thick biofilm was developed covering the whole thickness of the felt (1.2-cm deep), which coincided with high current densities and organics production rates. Current density reached up to −14 kA m−3electrode (−175 A m−2). Maximum sustained production rates of 9.8 ± 0.65 g L−1 day−1 C2, 3.2 ± 0.1 g L−1 day−1 nC4, and 0.95 ± 0.05 g L−1 day−1 nC6 were achieved (averaged between duplicates), at electron recoveries of 60–100%. Scanning electron micrographs revealed a morphologically highly diverse biofilm with long filamentous microorganism assemblies (~400 μm). n-Caproate is a valuable chemical for various industrial application, e.g., it can be used as feed additives or serve as precursor for liquid biofuels production.