Hydrogenotrophic activity under increased H2/CO2 pressure: Effect on methane production and microbial community

H2 and CO2 are main compounds of synthesis gas. Efficient conversion of syngas to biomethane is a straightforward strategy to integrate the energy value of syngas into existing natural gas grid infrastructures. In this study, the effect of initial H2/CO2 (80/20, v/v) pressure on methane production rate and microbial community diversity was assessed in a hyperbaric bioreactor inoculated with anaerobic granular sludge. Several batch experiments were performed to distinguish between the effect of initial total gas pressure and H2/CO2 partial pressure: (1) varying initial gas pressure (from 1 to 6 bar) with 100% H2/CO2 mixture; (2) constant initial gas pressure (5 bar), with increasing H2/CO2 partial pressure (from 1 to 5 bar); (3) varying initial gas pressure (from 2 to 5 bar) with constant H2/CO2 partial pressure (2 bar). In (2) and (3), N2 was used for ensuring the necessary overpressure. Microbial community changes in the system were monitored by 16S rRNA-based techniques (PCR-DGGE). The raise of H2/CO2 initial pressure (100% H2/CO2) from 1 to 5 bar led to an improvement in methane rate production from 0.035 ± 0.014 mmol h-1 to 0.072 ± 0.019 mmol h-1. Similar methane production rates were observed in reactors operated at the same H2/CO2 partial pressures, even when varying the total initial gas pressure. Hydrogen partial pressure was shown to determine the structure of bacterial communities and diversity decreased with increasing H2/CO2 partial pressure. No significant changes were observed for the archaeal communities