Contribution analysis of methane production from food waste in bulk solution and on bio-electrode in a bio-electrochemical anaerobic digestion reactor

• Published in: The Science of the total environment 2019-06, Vol.670, p.741-751
• Main Authors: Park, Jun-Gyu, Lee, Beom, Kwon, Hye-Jeong, Jun, Hang-Bae
• Format: Article
• Language: English
• Subjects: Bio-electrochemical anaerobic digestion (BEAD); Biofilm; Bulk solution; Methane production; Microbial communities
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.02.112

Quantitative evaluation of methane production either in bulk sludge or biofilm on electrodes was performed in a bio-electrochemical anaerobic digestion (BEAD) reactor with a lower electrode surface area/reactor working volume (A/V) ratio (7.0 m2/m3). Methane production by electrochemical reaction was also evaluated in the BEAD reactor with a biofilm-free electrode under the same conditions as in other experimental sets. The contributions of bulk sludge, biofilms on the electrodes, and electrochemical reactions in the BEAD reactor, on methane production, were 70.2%, 29.8%, and 0%, respectively. The principal methane-producing reactions occurred in the bulk sludge facilitated by H2-dependent methylotrophic and hydrogenotrophic methanogens. Hydrogenotrophic methanogenesis was also the main methane-producing reaction in the biofilms attached to the bio-electrodes. Quantitative analysis of methane production (29.8%) in the biofilm revealed that bio-electrochemical processes involving H2 and direct bio-electrochemical methane production contributed 8.7% and less than 0.1%, respectively. Interestingly, biochemical processes (21.1%) contributed the most to the overall production of methane in the biofilm. Bulk sludge contributed more to methane production than the biofilm, but the methane production per unit mass of volatile solid on the electrodes was about 1.6-times higher than that of bulk sludge. Methane was not produced in the BEAD reactor with biofilm-free electrodes. Therefore, formation and maintenance of biofilms on the electrodes are essential for improved methane production in BEAD reactors. [Display omitted] •Effect of bulk sludge and biofilm on methane production in BEAD was evaluated.•CH4 production by H2-dependent methanogens is the main reaction in the bulk.•Biochemical CH4 production is the main reaction in the biofilm.•The bulk and the biofilms in BEAD contribute 70.2% and 29.8% to CH4 production.