ABSTRACT
In the anaerobic digestion (AD) process microorganisms convert organic material into biogas under anaerobic conditions. In man-made engineered systems, biogas is produced at sewage treatment plants, in AD plants from industrial and municipal biowastes as well as in farm AD plants from agricultural feedstocks such as manure, crop residues and energy crops. Biogas is also produced in landfills. The biogas composition varies in different production sites with methane (CH4) and carbon dioxide (CO2) as the main components while sulphide compounds are typically present as well as various trace compounds including siloxanes. CH4 is the main energy component in the biogas, while it is also a strong greenhouse gas (GHG). Biogas, similar to natural gas, is typically used for combined heat and power (CHP) generation and increasingly as vehicle fuel and for distribution through the natural gas grid. Moisture, dust and sulphur (S) compounds are typically removed before any energy use, for example to prevent corrosion. For vehicle use and natural gas grid injection as well as for some CHP applications, removal of CO2 and other contaminants is needed to produce high value product, referred to as biomethane. This chapter presents biogas composition and its upgrading for biomethane production with emphasises on CO2 removal.
