BROMMA RENINGSVERKS UTLOPP TILL SALTSJÖN-SALTSJÖTUNNELN / The Outlet from the Bromma Sewage Treatment Plant to the Sea - a Full Face Tunnel Boring Project
Bromma sewage treatment plant for 260,000 persons has its outlet in Lake Mälaren, which also serves the greater Stockholm region as a source of drinking water. The erection of a heat pump 4 km from the plant has opened the possibility to choose another more suitable receiving water in the sea outside Stockholm. The heat pump takes the energy from the treated sewage water. Instead of returning the cold water to Mälaren, a tunnel 7.5 km long will be built deep under the city of Stockholm with the outlet in the sea. For the tunnelling there will be used a full face tunnel boring machine (TBM) with a diameter of 3.5 m. The heat pump is already running and the outlet tunnel to the sea will be finished at the end of 1988.