Biogas treatment for H2S, CO2, and other contaminants removal

The gradual depletion of fossil fuels along with the need to use renewable energy sources to mitigate climate change has triggered the development of biomethane as a green alternative of natural gas, where biomethane is obtained via upgrading the biogas obtained by anaerobic digestion of organic substrates. Overall, the inherent presence of multiple contaminants in biogas (CO2, H2S, and siloxanes) requires an effective purification prior injection into natural gas grids or use as a vehicle fuel. Recently, /chemical technologies such as water/organic/chemical scrubbing, pressure swing adsorption, or membrane separation dominate the market of biogas upgrading, with membrane separation gradually increasing its share in the CO2 removal sector. Biotechnologies based on hydrogenotrophic CO2 reduction to CH4 (power-to-gas), algal–bacterial symbiosis, or chemolithotrophic H2S oxidation have been tested in the laboratory under multiple bioreactor configurations and are currently under validation at a pilot scale. Biotechnologies for siloxane removal are, however, at an embryonic stage, with two-phase partitioning bioreactors showing promising results. This review describes the fundamentals and discusses the recent trends in biogas emerging upgrading biotechnologies.