A comparison of microbial and bioelectrochemical approaches for biogas upgrade through carbon dioxide conversion to methane

This study compares microbial and bioelectrochemical methods of biogas upgrade via CO2 conversion to CH4. First, an in situ approach for CO2 conversion is investigated in an anaerobic reactor with a continuous supply of exogenous H2. This approach increased CH4 content of the biogas to 80–85%, yet also increased the effluent acetate concentration to 5,000–6,000 mg L−1 due to homoacetogenic activity. In a second approach, an anaerobic biofilter was continuously fed with biogas and an exogenous supply of H2, resulting in a CH4 content of 85–90% and a H2 consumption of 4.2–4.5 mol per mol of CO2 removed. Finally, biogas upgrade via CO2 to CH4 conversion was demonstrated in the cathode compartment of a membraneless microbial electrosynthesis cell. This test resulted in a CH4 purity of 85 – 90% and an energy consumption (per L of treated biogas) of 3.1 ± 1.6 Wh L−1.