Biogas is a combustible gas mixture that is produced by the fermentation of biomass. The typical fermentation substrate is sewage sludge, organic waste or food waste, manure, agricultural waste (such as cover crops, crop residues etc.), as well as specially cultivated energy plants (renewable raw materials). Biogas is produced by the microbial degradation of organic matter under anaerobic conditions.
Biogas can be used for electricity and heat production in a CHP gas engine, or it can be cleaned in a biogas upgrader to reach the same quality as fossi-derived natural gas and then injected into the natural gas grid or used as vehicle fuel (Bio-CNG). If fed into the natural gas grid, the upgraded biogas (often referred to as biomethane) is obliged to fulfill the quality criteria defined by the relevant laws, e.g. the ÖVGW G31 and G33 in Austria. If used as fuel for CNG -vehicles, different regulations apply, e.g. the BGBL 417-II 2004. The table below compares biogas composition with standardized compositions of natural gas and CNG.