Addition of a carbon fiber brush improves anaerobic digestion compared to external voltage application

Abstract
Two methods were examined to improve methane production efficiency in anaerobic digestion (AD) based on adding a large amount of surface area using a single electrically conductive carbon brush, or by adding electrodes as done in microbial electrolysis cells (MECs) to form a hybrid AD-MEC. To examine the impact of surface area relative to electrodes, AD reactors were fitted with a single large brush without electrodes (FB), half a large brush with two electrodes with an applied voltage (0.8 V) and operated in closed circuit (HB-CC) or open circuit (HB-OC) mode, or only two electrodes with a closed circuit and no large brush (NB-CC) (equivalent to an MEC). The three configurations with a half or full brush all had improved performance as shown by 57-82% higher methane generation rate parameters in the Gompertz model compared to NB-CC. The retained biomass was much higher in the reactors with large brush, which likely contributed to the rapid consumption of volatile fatty acids (VFAs) and therefore improved AD performance. A different microbial community structure was formed in the large-size brushes compared to the electrodes. Methanothrix was predominant in the biofilm of large-size carbon brush, while Geobacter (anode) and Methanobacterium (cathode) were highly abundant in the electrode biofilms. These results demonstrate that adding a high surface area carbon fiber brush will be a more effective method of improving AD performance than using MEC electrodes with an applied potential.

Citation
Baek, G., Saikaly, P. E., & Logan, B. E. (2020). Addition of a carbon fiber brush improves anaerobic digestion compared to external voltage application. Water Research, 116575. doi:10.1016/j.watres.2020.116575

Acknowledgements
This research was funded by the Stan and Flora Kappe endowment and other funds through The Pennsylvania State University.

Publisher
Elsevier BV

Journal
Water Research

DOI
10.1016/j.watres.2020.116575

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S0043135420311106

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