The Biogas

Biogas composition

CH4

Biogas is characterized based on its chemical composition and the physical characteristics which result from it. It is primarily a mixture of methane (CH4) and inert carbonic gas (CO2). However the name “biogas” gathers a large variety of gases resulting from specific treatment processes, starting from various organic waste - industries, animal or domestic origin waste etc

Chemical composition

Different sources of production lead to different specific compositions. The presence of H2S, of CO2 and water make biogas very corrosive and require the use of adapted materials. The composition of a gas issued from a digester depends on the substrate, of its organic matter load, and the feeding rate of the digester

Components	Household waste	Wastewater treatment plants sludge	Agricultural wastes	Waste of agrifood industry
CH4 % vol	50-60	60-75	60-75	68
CO2 % vol	38-34	33-19	33-19	26
N2 % vol	5-0	1-0	1-0	-
O2 % vol	1-0	< 0,5	< 0,5	-
H2O % vol	6 (à 40 ° C)	6 (à 40 ° C)	6 (à 40 ° C)	6 (à 40 ° C)
Total % vol	100	100	100	100
H2S mg/m3	100 - 900	1000 - 4000	3000 – 10 000	400
NH3 mg/m3	-	-	50 - 100	-
Aromatic mg/m3	0 - 200	-	-	-
Organochlorinated or organofluorated mg/m3	100-800	-	-

Physical characteristics

According to its composition, biogas presents characteristics interesting to compare with natural gas and propane. Biogas is a gas appreciably lighter than air, it produces twice as less calories by combustion with equal volume of natural gas.

Types of gas	Biogas 1 Household waste	Biogas 2 Agrifood industry	Natural gas
Composition	60% CH4 33 % CO2 1% N2 0% O2 6% H2O	68% CH4 26 % CO2 1% N2 0% O2 5 % H2O	97,0% CH4 2,2% C2 0,3% C3 0,1% C4+ 0,4% N2
PCS kWh/m3	6,6	7,5	11,3
PCI kWh/m3	6,0	6,8	10,3
Density	0,93	0,85	0,57
Mass (kg/m3)	1,21	1,11	0,73
Indiex of Wobbe	6,9	8,1	14,9

The Biogas

Biogas composition

Chemical composition

Physical characteristics

Headings: