Biogas upgrading methods: recent advancements and emerging technologies

Biogas is a valuable product of the anaerobic digestion process, which is used for the generation of renewable energy. The main component of biogas is methane together with impurities like carbon dioxide water vapour, hydrogen sulphide, siloxanes, hydrocarbons, ammonia, oxygen, carbon monoxide and nitrogen. Their presence is undesired, reducing the calorific value of biogas and creating various operational problems on machines. Therefore, multi-stage technologies for their removal are used during the process of transformation of biogas to biomethane. This paper presents the most used physicochemical technologies for biogas upgrading and CO2 removal with the addition of novel findings and further possibilities of their improvements. Compared are their costs, energy requirements, removal efficiency and other parameters to give the reader a more complex view on their competitiveness. The review also includes a comprehensive description of chemotrophic as well as phototrophic methods of hydrogen sulphide treatment with a focus on biological means. Although these methods are not always feasible when compared with physicochemical counterparts, they offer attractive advantages, including lower cost and more environmentally friendly operation with greater possibilities of improvement.