Enhanced methane production from cellulose using a two-stage process involving a bioelectrochemical system and a fixed film reactor

• Main Authors: Kondo, A. (Author), Morita, M. (Author), Sasaki, D. (Author), Sasaki, K. (Author), Tsuge, Y. (Author)
• Format: Article
• Language: English
• Published: BioMed Central Ltd 2021
• Subjects: Anaerobic digestion; Anaerobic digestion process; Bio-electrochemical; Bioelectrochemical system; Bio-electrochemical systems; Bioelectrochemical systems (BES); biofilm; Carbon Fibers; Cellulolytic bacterium; cellulose; Cellulose; Cellulosic material; Clostridium; Conductive materials; Electrochemical systems; Electrodes; Entertainment industry; experimental study; Fixed film reactor; Graphite fibers; Hydraulic retention time; Hydrogen production; Hydrogenotrophic methanogen; methane; Methane; Methanobacterium sp.; Methanogens; Methanosarcina sp.; Microbial fuel cells; molecular analysis; Nucleic Acids; pollutant removal; Processes; Productivity; Regenerative fuel cells; RNA; Systems; Two-stage process
• Online Access: View Fulltext in Publisher

 Background: It is desirable to improve the anaerobic digestion processes of recalcitrant materials, such as cellulose. Enhancement of methane (CH4) production from organic molecules was previously accomplished through coupling a bioelectrochemical system (BES); however, scaling-up BES-based production is difficult. Here, we developed a two-stage process consisting of a BES using low-cost and low-reactive carbon sheets as the cathode and anode, and a fixed film reactor (FFR) containing conductive material, i.e., carbon fiber textiles (CFTs) (:BES → FFR). By controlling the cathodic current at 2.7 μA/cm2 without abiotic H2 production, the three-electrode BES system was operated to mimic a microbial electrolysis cell. Results: The thermophilic BES (inlet pH: 6.1) and FFR (inlet pH: 7.5) were operated using hydraulic retention times (HRTs) of 2.5 and 4.2 days, respectively, corresponding to a cellulose load of 3555.6 mg-carbon (C)/(L day). The BES → FFR process achieved a higher CH4 yield (37.5%) with 52.8 vol% CH4 in the product gas compared to the non-bioelectrochemical system (NBES) → FFR process, which showed a CH4 yield of 22.1% with 46.8 vol% CH4. The CH4 production rate (67.5 mM/day) obtained with the BER → FFR process was much higher than that obtained using electrochemical methanogenesis (0.27 mM/day). Application of the electrochemical system or CFTs improved the yields of CH4 with the NBES → FFR or BES → non-fixed film reactor process, respectively. Meta 16S rRNA sequencing revealed that putative cellulolytic bacteria (identified as Clostridium species) were present in the BES and NBES, and followed (BES→ and NBES→) FFR. Notably, H2-consuming methanogens, Methanobacterium sp. and Methanosarcina sp., showed increased relative abundances in the suspended fraction and attached fraction of (BES→) FFR, respectively, compared to that of (NBES→) FFR, although these methanogens were observed at trace levels in the BES and NBES. Conclusions: These results indicate that bioelectrochemical preprocessing at a low current effectively induces interspecies H2 transfer in the FFR with conductive material. Sufficient electrochemical preprocessing was observed using a relatively short HRT. This type of two-stage process, BES → FFR, is useful for stabilization and improvement of the biogas (CH4) production from cellulosic material, and our results imply that the two-stage system developed here may be useful with other recalcitrant materials. © 2021, The Author(s).