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.