Enhanced bioconversion of hydrogen and carbon dioxide to methane using a micro-nano sparger system: mass balance and energy consumptionElectronic supplementary information (ESI) available. See DOI: 10.1039/c8ra02924e

Simultaneous CO 2 removal with renewable biofuel production can be achieved by methanogens through conversion of CO 2 and H 2 into CH 4 . However, the low gas-liquid mass transfer ( k L a ) of H 2 limits the commercial application of this bioconversion. This study tested and compared the gas-liquid mass transfer of H 2 by using two stirred tank reactors (STRs) equipped with a micro-nano sparger (MNS) and common micro sparger (CMS), respectively. MNS was found to display superiority to CMS in methane production with the maximum methane evolution rate (MER) of 171.40 mmol/L R /d and 136.10 mmol/L R /d, along with a specific biomass growth rate of 0.15 d −1 and 0.09 d −1 , respectively. Energy analysis indicated that the energy-productivity ratio for MNS was higher than that for CMS. This work suggests that MNS can be used as an applicable resolution to the limited k L a of H 2 and thus enhance the bioconversion of H 2 and CO 2 to CH 4 . Simultaneous CO 2 removal with renewable biofuel production can be achieved by methanogens through conversion of CO 2 and H 2 into CH 4 . However, the low gas-liquid mass transfer ( k L a ) of H 2 limits the commercial application of this bioconversion.