The treatment plant is currently made up of two parts: one plant in Henriksdal and another in Sickla. Changes are made at both the Sickla plant and the Henriksdal plant, and all refurbishment work will be carried out while the treatment plant is operational.
The treatment plant will be equipped with new biological treatment facilities and one of the biggest membrane filtration plants in the world. Membrane bioreactor technology (MBR) will allow us to treat larger quantities of wastewater more effectively than before. We will also improve pre-treatment and sludge treatment.
In the biological treatment stage, organic matter and nitrogen are removed with the help of microorganisms (known as active sludge). Converting our existing process to membrane bioreactors (MBR) will allow us to increase treatment capacity without increasing storage pond volume. The old post-sedimentation ponds where biological sludge is separated from the treated wastewater will be converted into a modern membrane plant that is considerably more efficient. This will allow us to more than double the sludge content in the bioponds, which will more than double the treatment capacity. The new process will also allow us to reduce output levels of nitrogen, phosphorus and organic materials so that we meet the stricter new treatment requirements. The membranes also screen out microplastics, bacteria and a large proportion of viruses from the water phase.
The membrane plant is susceptible to rubbish that may accumulate in the biological treatment facility and destroy the equipment. We have therefore improved treatment handling at the primary treatment stage, installing a new perforated sheet screens at the inlet to the biological treatment facility.
A new, high-flow treatment facility will be needed in order to deal with the high flows arriving at the treatment plants during periods of heavy rainfall or sustained melting of snow, so as to treat the wastewater that cannot be accommodated by the biological treatment stage. High-flow treatment will involve reinforced chemical treatment in the pre-sedimentation ponds, with subsequent final polishing in the sand filters. We will therefore be building a new station for chemical coagulants, widening the inlets to the pre-sedimentation ponds and preparing the sand filters for periodic operation.
The high load at the Henriksdal treatment plant in future will generate considerably larger sludge volumes than is currently the case. A more efficient digestions process will therefore be required in order to stabilise the sludge and extract the energy bound up in it. Therefore, we will be constructing a new facility for thickening the sludge and preparing for a more efficient digestion process.
The digested sludge is currently dewatered and loaded at the Sickla plant. A new dewatering plant with a built-in sludge loading facility will be constructed at Henriksdalsberget, which will reduce the risk of odour problems for people living nearby.
Total length of the tunnel will be 1100 metres. We are building this tunnel because there will be no room for the technology (electricity, ventilation and networks, that is) at the existing treatment plant.
Positioning the technology above the storage ponds also has its advantages.
