The Henriksdal Wastewater Treatment Plant (WWTP) is upgrading its membrane bioreactor (MBR). Soon, it will become the largest MBR WWTP plant in the world.
Henriksdal WWTP is located on the boundary between Stockholm and Nacka, approximately 2km from Slussen, Sweden. It serves over one million people in Stockholm, Huddinge and the surrounding municipalities.
Stockholm has one of the fastest growing populations in Europe. Stockholm Vatten, the city’s water company, are responding to population growth by developing the capacity of the WWTP facility. The company are also producing a higher quality effluent to match the country’s environmental commitments under the Baltic Sea Action Plan (BSAP) and the E.U. Water Directive. They are replacing the plant’s current MBR for the treatment.
The city of Stockholm is big; therefore, the plant is relatively big. In fact, Henriksdal is one of the largest underground WWTP’s in the world; it has a total area of 300,000m³, 18km of associated tunnels and pipe network, and a wastewater treatment capacity of 250,000m³ a day. The facility is responsible for treating two thirds of the municipal wastewater for the city.
Henriksdal’s construction history is full bodied and comprehensive. The WWTP has been treating wastewater for almost 70 years. It opened in 1941 with a daily wastewater treatment capacity of 150,000m³. By 1953, this doubled to 300,000m³. Chemical and biological treatment facilities were then incorporated into the plant’s system.
In the 1960’s, the WWTP started to extract energy (biogas and biochar) from sludge residues. The sludge has been an invaluable resource for the city, versatile enough to fuel buses and grow crops. As much as 50 per cent of the biogas produced in wastewater treatment is now converted into vehicle fuel, and, all the remaining biogas is used as soil conditioner. The sludge gets treated at the neighbouring facility in Sickla.
More recently, significant changes have been made. From the early 90’s through to the late 2000’s, Henriksdal went under considerable reforms.
A major expansion took place between April 1992 to April 1997. The expansion helped the plant to reduce nitrogen emissions by approximately 50%. It also facilitated profound improvements to the phosphorus treatment process.
In 2007 to 2011, there was a second development. This involved the construction of a new hall for rough purification. In addition, considerable work improved the receiving station for grease and organic waste. 80,000m³ of rock was blasted and excavated for this part of the project: it cleared a space underground, so the odorous facilities could be reconstructed and placed away from the surface. In addition, further rock clearance facilitated the development of 3,000 new homes around Henriksdalsberget.
Now, the facilities at the WWTP systematically provide a variety of processes and solutions to wastewater treatment. The WWTP treats wastewater using mechanical, chemical, biological and sand filtration processes. The treated water is then returned into the Baltic Sea. The biogas produced from the plant is used as fuel in the plant’s heat production system for the production of electricity and for producing biomethane for fueling vehicles, while the sludge is used as a soil conditioner.
It is interesting to consider the equipment that deals with these processes. Henriksdal WWTP is currently equipped with eight mechanical screens, two grit chambers with a volume of 590m³ each and two pre-aeration channels with a capacity of 260m³ each. It also contains 13 primary sedimentation tanks with a combined volume of 30,000m³, nine pumping stations to lift the primary-sedimentation to the biological stage, seven aeration tanks with a combined volume of 204,000m³ and 19,000 aerators, five aerator compressors, and 14 secondary sedimentation tanks with a combined volume of 58,000m³.
The plant is also equipped with 12 pumps to lift the water from the biological stage to 60 sand filters, seven digesters with a combined volume of 39,000m³, a heat exchanger digester sludge, a 5,000m³ gas holder, five excess sludge centrifuges with a capacity of 50m³ a hour, two sludge tanks with a combined volume of 10,000m³, four centrifuges with a capacity of 30m³/h each for dewatering of sludge, two silos of 800m³ each for containing dewater sludge, four gas engines, three boilers and associated facilities.
90% of the facilities are currently located underground. However, there is still a need for some surface facilities, such as the control centre building, mechanical treatment facilities, sludge tanks and upper parts of the sludge thickeners. The digesters, gas holder, and gas collection and gas storage facilities are also located above ground. The plant’s old ventilation chimney measuring 80m-high and 7m in diameter is currently being reinforced with concrete.
The plant is functional and effective, but it has been increasing its capabilities by updating treatment technology in order to match city growth. According to Gösta Lindh, managing director of Stockholm Vatten:
“We saw the need to update the current wastewater treatment technology at our Henriksdal facility to meet the demands of a growing population in Stockholm and new environmental requirements set by our governing bodies”.
“GE’s LEAPmbr and ZeeWeed* technology will help us meet our long-term needs for increased wastewater treatment capacity and will help us do so in a more energy-efficient and cost-effective manner.”
The ZeeWeed upgrade is part of the new MBR development. This process began with a pilot in 2014 to test the MBR technology against a load equal to Stockholm’s projected population in 2014.
The pilot test was performed at IVL’s (Swedish Environmental Research Institute) Hammarby Sjöstadsverk research facility. The test produced positive and favourable results, which encouraged the current MBR upgrade project.
In addition to the new membrane distillation units on site, the project requires the construction of a 15km underground tunnel, bored from 30m to 90m below ground level. This will divert the wastewater from Bromma to Henriksdal. A new pre-treatment facility comprised a new pump station, new coarse screening and primary sedimentation basins will also be built at Sickla.
The decommissioning of the Bromma WWTP will start following the commissioning of the revamped Henriksdal WWTP.
Several construction bodies will assist Henriksdal development. So far, Sweco led the major components of the project, including the pre-feasibility study to detailed design and construction followed by the supervision and commissioning of the plant.
Lemminkäinen constructed a 400metre long access tunnel for Stockholm Vatten in order to renovate the water basins for their future capacity improvements.
GE will provide Stockholm Vatten with membrane bioreactor equipment for the WWTP facility to upgrade the existing technology. This will make it the largest MBR plant in the world.
As part of the contract, GE will be delivering a scope that encompasses the design, supply and servicing of the entire membrane filtration package. The contract will be completed in multiple stages and delivered over a period of four to five years. Design will be completed in 2015 and first shipments will begin in 2016.
Mobilaris´ system have been chosen to raise issues over personal safety at Henriksdal purification plant. According to Micael Bäckström at Stockholm Vatten & Avfall, Mobilaris has good support for integrating the security system into the existing facility.
Once the MBR upgrade is complete, the services and capabilities of Henriksdal wastewater treatment will serve this ever growing, ever changing city better than before.