Biogas composition
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 |
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