Addition of a carbon fiber brush improves anaerobic digestion compared to external voltage application. (1st January 2021)

• Record Type: Journal Article
• Authors: Baek, Gahyun; Saikaly, Pascal E.; Logan, Bruce E.
• Is Part Of: Water research. Volume 188(2021)
• Publication Date: 2021-01-01
• Subjects: Anaerobic digestion -- carbon brush -- microbial community structure -- microbial electrolysis cell -- surface area; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.116575
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Large conductive surface areas were compared to the use of electrodes in AD Adding a large carbon brush improved performance more than current generation More biomass could be retained on the large carbon brush than small-size electrodes Methanothrix was dominant methanogens on the large-size carbon brush Geobacter and Methanobacterium were highly enriched on the electrodes 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 voltage. Graphical abstract: Image, graphical abstract