Biogas is the gaseous product of anaerobic digestion, a biological process in which microorganisms break down biodegradable material in the absence of oxygen. Biogas is comprised primarily of methane (50%–70%) and carbon dioxide (30%–50%), with trace amounts of other particulates and contaminants. It can be produced from various waste sources, including land ll material; animal manure; wastewater; and industrial, institutional, and commercial organic waste. Biogas can also be produced from other lignocellulosic biomass (e.g., crop and forest residues, dedicated energy crops) through dry fermentation, co-digestion, or thermochemical conversions (e.g., gasification).
Biogas can be combusted to provide heat, electricity, or both. In addition, it can be upgraded to pure methane— also called biomethane or renewable natural gas—by removing water, carbon dioxide, hydrogen sulfide, and other trace elements. This upgraded biogas is comparable to conventional natural gas, and thus can be injected into the pipeline grid or used as a transportation fuel in a compressed or liquefied form. Renewable natural gas is considered a “drop-in” fuel for the natural gas vehicles currently on the road.
Similar to other fuels, biomethane requires a distribution infrastructure using dedicated retailing stations supplying only biomethane (compressed or liquefied). Alternatively, certification schemes or other mechanisms can be applied allowing consumers to buy the equivalent of biomethane while using a regular natural gas refilling station. In 2016, approximately 1% of the biogas produced in the EU+EFTA was used for transport (Eurostat).