Static hydrodynamic cavitation as external gas-liquid transfer system for biological biogas upgrading

The study deals with the use of a static hydrodynamic cavitation device as a gas-to-liquid mass transfer system to provide the biological conversion of carbon dioxide into methane in a dedicated bioreactor. An orifice plate hydrodynamic cavitation device was coupled with a thermophilic pilot-scale bioreactor inoculated with a mixed inoculum sampled from a centralized full-scale anaerobic digester treating sewage sludge. The bioreactor was fed with hydrogen and carbon dioxide and then, with a mix of hydrogen and biogas, and monitored in terms of process efficiency and stability. Gas sparging through the static hydrodynamic cavitation device was feasible under the operating conditions applied, allowing to achieve a methane concentration above 96% in the gas produced and a hydrogen solubilization efficiency of about 100% without compromising biological stability. However, during the biogas upgrading experimental stage a significant foam formation was observed in the reactor headspace, which led to a lower bioavailability of the CO2 and increased complexities in process management.