Biomethane —also known as renewable natural gas (RNG) or Sustainable Natural Gas (SNG)— is the methane produced from biomass. It has similar properties to natural gas. Biomethane is renewable, because it is obtained from renewable organic matter (biomass), following treatment of the biogas obtained in the anaerobic digestion process.
During the anaerobic digestion processes, the organic matter is broken down by bacteria in the absence of oxygen to produce biogas and a sludge containing most of the inorganic substances (nitrogen, phosphorus, etc.), together with other non-biodegradable compounds.
Biogas is generated at municipal solid waste (MSW) landfills, as a result of breakdown of the accumulated organic matter. It can also be produced in reactors or digesters that process biomasses with a high organic matter content: sludge from wastewater treatment plants (WWTPs), waste from arable and livestock waste, etc.
Biogas is a mixture of gases, containing 40–70 % methane (CH4), 30–40 % CO2, 2–8 % of H2O and traces of other compounds such as SH2, O2, N2, NH3, siloxane and particulates. It has to be treated using a cleaning process and upgraded to obtain BM.