To stop eutrophication of the sea, Gryaab treats the Gothenburg region waste water. The residue, sewage sludge, is turned into soil, fertilizer and a climate-friendly vehicle fuel.
Each year, approximately 55,000 tonnes of sludge are produced at Gryaab. The treated sludge contains nutrients and mulch – what is needed for crops to grow. Some of the decayed sludge is composted and used as construction soil. About half of the sludge is hygienised and used as fertiliser, replacing artificial fertiliser.
Gryaab receives approximately 4,000 litres of water per second. It is cleansed from nitrogen, phosphorus and organic matter, which if released into the sea would lead to eutrophication and oxygen depletion. Treatment is mechanical. chemical and biological. Mechanical treatment involves grids and scrapers; chemical treatment, ferrous sulphate that precipitates phosphorus; and biological treatment, the bacteria found naturally in wastewater. They convert ammonium into nitrogen and break down the organic material.
– The plant is fully automated, so staff do not have to work around the clock.
– Every year Gryaab produces more than 70 GWh of biogas, which is sold to Göteborg Energi and upgraded to 95–98 per cent methane.
– Göteborg Energi compresses the biogas and sells it as vehicle fuel.
– Gryaab produces enough biogas in a year to drive a car 2 500 times around the globe.
– The facility also receives fat and food waste from restaurants, schools, and food producers in the region.
– It is a multi-award-winning disc filter structure that has won both the Kasper Sahlin prize and the Stålbyggnadspriset (Steel Building Prize).
– The plant is tall and thus has a small footprint, which serve as inspiration for those who build in developed areas.
– An extension is planned in order to meet any stricter treatment requirements after 2036.