Biogas and biofertilizer
Biogas is methane gas produced from organic material such as leftovers, sewage sludge, manure and plants. Biogas is formed when the material is broken down by microorganisms in an oxygen-free environment. This process is called digestion and takes place in a digester.
VafabMiljö owns a biogas plant located at Gryta in Västerås. In the plant the leftovers are mixed with sludge from grease and forage crops. Hay crops are mixed grasses such as timothy and clover. It takes about 20 days for the material to decompose. From the digester, we get both biogas and fertilizer. The biogas is used as fuel for vehicles such as buses, trucks and cars.
To use biogas to vechicles, the methane must content higher methane than it does when it comes out of the digester. When the gas is ready in the digester it contains about 65 percent methane and 35 percent carbon dioxide. To serve as a vehicle fuel, the methane gas has to be about 97 percent. To raise the level of methane gas, it is send to the upgrading plant where the carbon dioxide is washed away. This is done by means of water at 10 bar pressure. The biogas is then ready to be sent to filling stations throughout our region.
Today biogas is counted as one of the world’s most environmentally friendly vehicle fuels.
- Biogas – methane gas from renewable energy sources
- Natural gas – methane from fossil sources
- CNG – generic name for both biogas and natural gas
During the digestion process it also produces bio-fertilizer, this is used by farmers to supply essential nutrients back into the soil. Biofertiliser is a locally produced alternative to mineral or chemical fertilizers. The farmers collect the manure on our facility to spread out on the fields again.
Farmers grow forage crops around Västerås. A valuable crop, both for agriculture and for the biogas plant. A total cultivated about 200 hectares cloverrich grassland for energy.
Vall cultivation is important for the biogas plant, for it´s raw material for energy. The dike is harvested once or twice every year and stored as silage adjacent to the plant. Subsequently, the embankment along with food particles to be digested into biogas and digestate.