Feasibility test anaerobically enhancing methane yield under the injection of hydrogen and carbon dioxide

The anaerobic conversion of surplus hydrogen to methane by hydrogenotrophic methanogen in an anaerobic digester has been attempted to overcome the drawbacks of hydrogen uselessly escaped from small or middle-scale industries. A biochemical methane potential test was thus performed to evaluate the methane production from hydrogen and carbon dioxide (H₂/CO₂ = 4:1) injected directly into the reactors at mesophilic temperature (38 °C) for 30 days. The cumulative methane yield increased stepwise, ultimately reaching a maximum of 143.94 NmL CH₄/g VS_add at the end of the experiment, which was 56% higher than the control. After 7 days of incubation, the methane content in the biogas accounted for about 90%, whereas the control showed 10% lower than that. The kinetic study showed the injection of H₂/CO₂ could reduce the rate of hydrolysis, verifying that the experimental data fit the first-order model better. In the meantime, microbial community analysis showed an increase in relative abundance of hydrogenotrophic methanogens, Methanobacteriales and Methanomicrobiales, in the sludge obtained after the test compared to before, indicating the increased methane yield was dominantly attributed to hydrogenotrophic methanogenesis. This study demonstrated that H₂/CO₂ injection directly into the anaerobic digester was feasible for ultimately enhancing the quality of biogas.