Composition

Typical composition of biogas^[2]

Matter	%
Methane, CH4	50-75
Carbon dioxide, CO2	25-50
Nitrogen, N2	0-10
Hydrogen, H2	0-1
Hydrogen sulfide, H2S	0-3
Oxygen, O2	0-2

The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55-75%CH₄ ^[3].

Main article: Siloxanes

In some cases biogas contains siloxanes. These siloxanes are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or various other elements in the combustion gas. Deposits are formed containing mostly silica (SiO₂) or silicates (Si_xO_y) and can also contain calcium, sulfur, zinc, phosphorus. These white mineral deposits build to a surface thickness of several millimetres and must be removed by chemical or mechanical means.