Bioconversion of H2 and CO2 from dark fermentation to methane: Effect of operating conditions on methane concentration

Abstract

The main goal of this study was to assess the methane production in a biotrickling filter (BTF) using a synthetic gas mixture (H2/CO2: 60/40), evaluating the effect of the empty bed gas residence time (EBRT), pH, and temperature. The BTF was inoculated with acclimated granular anaerobic sludge. Three EBRT were tested: 11.6, 5.8, and 2.9 h. The decrease in EBRT (from 11.6 to 5.8 h) increased 1.3-fold the methane content (69 ± 3%) with H2 and CO2 removals of 100% and 24 ± 6%, respectively. The following reduction to 2.9 h showed no effect on CH4 content. The increment of the pH had no significant effect; however, the highest CH4 percentage (74%) was observed at a pH of 8.5. The system showed flexibility to adapt to changes in temperature without drastically diminishing CH4 concentration. In these stages, the principal hydrogenotrophic archaea detected was Methanobacterium flexile. Soluble microbial products such as butanol, caproate, and iso-valerate were detected in all the operating stages. This study demonstrates the potential of methane generation from a dark fermentation gaseous effluent.