The Water and Sewerage Authority treats the sewerage water from eastern parts of Oslo at Bekkelaget Treatment Plant. Discharge from approximately 300 000 person equivalents is treated with mechanical, chemical and biological purification including removal of nitrogen. The sludge is digested in digestion tanks at 55 degrees and is de-watered in centrifuges. The biogas which forms during the digestion is pumped to an upgrading facility where the gas is purified and upgraded to biomethane. This is compressed and used as fuel. The amount of upgraded gas is equivalent to 2 100 000 litre diesel equivalents. 45 buses and approximately 100 heavy vehicles are currently driven with upgraded biogas as the only fuel source.
The biogas project is one of Oslo kommune's most profiled environmental projects. The project ensures that more energy is produced than the entire treatment plant uses.