Biogas, a methane (CH4) rich gas produced from anaerobic digestion of organics, is a valuable renewable fuel. Upgrading biogas, the process of removing impurities and concentrating CH4, produces a cleaner, more useful/valuable fuel. While biogas can be upgraded to biomethane (>95% CH4, see footnote), a fuel that can be injected into natural gas grids or used in vehicles, this level of upgrading is cost prohibitive for most farms. More typical on-farm use of biogas is in boilers and engine-generator sets, where lower CH4 levels (>50%) can be used providing water and hydrogen sulfide (H2S) are removed. Combinations of demisters, condensation sumps, and chillers are used for dewatering. Many developed technologies remove H2S (desulfurization), and are highlighted below.