Why does Stockholm need a new wastewater treatment system?

Sweden has undertaken to reduce its emissions of phosphorus and nitrogen to the Baltic Sea, as these contribute to eutrophication. These measures are regulated in the Baltic Sea Action Plan and the EU’s Water Framework Directive. We also need to protect the water in Lake Mälaren, which is our drinking water source and a popular lake for swimming.

The project Stockholm's future wastewater treatment (SFA)

Henriksdal's wastewater treatment plant and the Sickla facility are being developed into one of the world's most modern plants, where we use new technology to purify more wastewater in the same area. The Bromma treatment plant, which is now which is now used to its limits and does not meet future environmental requirements, will be closed. The wastewater from Bromma will instead be led in a new sewage tunnel to be treated with the new technology in Henriksdal.

Environmental benefits with SFA

With efficient membrane technology in Henriksdal's wastewater treatment plant, we reduce emissions of nitrogen and phosphorus and can separate, for example, microplastics before the water is discharged into the Baltic Sea. With the new technology, we can live up to the increased environmental requirements of the future. 

With the new sewer tunnel, many discharge points along Lake Mälaren will be removed, which means that the emissions of untreated wastewater into the lake in the event of heavy rains will be reduced by 50%.

Another advantage of the project is that no malodorous sludge management will take place in the vicinity of residential areas in Åkeshov and Hammarby sjöstad.

Difficulties in expanding Bromma treatment plant

Bromma wastewater treatment plant has a significantly less purification of nitrogen than Henriksdal WWTP has. Preserving the Bromma treatment plant would require an upgrade of the capacity and an expansion of the plant.

The alternative of retaining and expanding the Bromma treatment plant was investigated prior to the decision. The investigations concluded that it was not a reasonable alternative. It is not possible to expand the shallow basins at the Åkeshov facility, as safety distances are required to the nearest buildings. In addition, there would be no possibility of future expansion for increased and improved purification and biogas management.

Environmentally and economically the best alternative

Concentrating operations on one wastewater treatment plant is best from an environmental point of view and is also the most cost-effective alternative.

With the alternative of keeping the Bromma treatment plant, we would lose several environmental benefits that we now get with the project. For example, reduced emissions of untreated wastewater into Lake Mälaren and more efficient and safer production of biogas. With that alternative, all water in Bromma could not be purified with membrane technology, which will now happen in Henriksdal.

The new sewer tunnel from Bromma to the Sickla facility is also an investment that enables a future expansion of housing in Söderort, as sewer from new buildings can be connected to the tunnel. Without the new sewage tunnel, new developments in Söderort would require a new long tunnel to the Sickla facility.

Future operating and reinvestment costs as well as investment in new technology would also be higher with two treatment plants.

The project's budget has been expanded since the decision in 2013. There are several reasons for this, but above all it is a very complex project and it takes longer than originally planned to rebuild a treatment plant that must be in operation at all times. Other reasons are subsequent decisions to increase capacity in the Sickla facility and more space is needed than originally planned for the technology in Henriksdal.

The calculation prior to the decision showed that the alternative of retaining the Bromma treatment plant would cost approximately SEK 1.3 billion less than the alternative chosen. Despite this, the Land and Environment Court decided that the closure of the Bromma treatment plant was the best alternative from an environmental and socio-economic point of view.