That is why the Henriksdal treatment plant is being developed to make it one of the most modern plants in the world. The Bromma treatment plant will be shut down, and a new wastewater tunnel will be established between Bromma and Henriksdal.
At least 1,2 million people are expected to be living in the City of Stockholm by 2040. This is why the Stockholm's Future Wastewater Treatment project has adopted a strategic, long-term approach with a view to handling wastewater treatment sustainably and efficiently by 2040.
When this project is complete, we will have secured an effective wastewater system for all of the city's residents while also effectively reducing the environmental impact on Lake Mälaren and the Baltic Sea.
Environmental, technical and socio-economic factors indicate that shutting down the Bromma treatment plant would be the best thing, concentrating wastewater treatment at the treatment plant in Henriksdal instead. A new tunnel will be constructed in order to channel wastewater from Västerort to Henriksdal. This is also what is implied by the decision made by Stockholm Municipal Council in May 2014.
The Bromma treatment plant is nowhere near as good at nitrogen treatment as Henriksdal. Retaining the Bromma plant would require upgrading its capacity and expanding the premises. But the Bromma treatment plant is located above ground in a densely populated area, and there has to be a safe zone of at least 200 metres around the plant. So it would be necessary to shut down the plant within ten to fifteen years anyway, as the buildings surrounding it would prevent it being expanded still further.
The Henriksdal plant is located below ground, in Henriksdalsberget, where there is plenty of space. The final stage in the treatment process at the new treatment plant will be replaced with modern membrane technology that is able to treat more water over a smaller area. Moreover, the water will will be cleaner than it is today. We will surpass environmental requirements by some way by 2040, and there will be space inside the mountain to expand the plant still further after that.
Emissions limits will be tightened up as these have to be reduced radically if the water in the Baltic Sea is to be made healthier. To meet the environmental requirements, therefore, we need extended capacity and modernisation of wastewater treatment in the city.
Lake Mälaren is important to Stockholm. We get our drinking water from there, lots of people sail leisure craft there in summer, and there are a number of popular swimming areas along its shores. At present, untreated water is released into Lake Mälaren as an emergency measure – overflow discharge – during periods of heavy rainfall. This would be avoidable if we could store the untreated water when necessary.
