Sara Toustrup Kristensen
February 26, 2025
Reviving Oslofjorden: Removal of Micropollutants and Nitrogen in Wastewater
Across four innovative Norwegian projects, Ramboll’s global water experts are collaborating with external partners and clients to significantly improve the health of Oslofjorden.
Years of pollution from nutrients like nitrogen have led to severe oxygen depletion in Oslofjorden, leaving the fjord in a critical state. Fish populations are nearly depleted, the lower growth limit for seaweed is decreasing, and algal blooms and slime are displacing other organisms. Discharge from wastewater treatment plants is still a major source of pollution, and therefore, improving wastewater treatment is a central initiative to help save Oslofjorden.
Municipalities and treatment plants are anticipating stricter EU regulations for wastewater discharge, targeting the volume of discharge as well as the acceptable level of micropollutants and nitrogen emissions. Following the recently published report on the condition of Oslofjorden by the Norwegian Institute for Water Research, these initiatives seem more important than ever.
Nitrogen from sewage and agriculture together accounts for around 75 percent of the nitrogen that flows into the Oslo Fjord. Therefore, it’s very positive that a lot of municipalities are now actively working on plans for improving wastewater treatment, and that stricter requirements are in place for farmers to reduce plowing of grain fields in the fall.
Together with Hollinger and our visionary clients Oslo Municipality, Søndre Follo WWTP (SFR), and Vestfjorden Wastewater Treatment Plant (VEAS), Ramboll is tackling this challenge as an opportunity to test and implement new and innovative technologies across the projects.
Improved nitrogen-removal at Bekkelaget WWTP
Although Bekkelaget Wastewater Treatment Plant has already undergone a successful process of nitrogen removal, those admirable efforts might not suffice in the future. Ramboll is therefore working with Bekkelaget to reach their new goal, aiming to increase Bekkelaget’s treatment efficiency.
The project entails mapping of current operations of the plant to optimize management and explore the use of new technologies. Ramboll has already started pilot-testing. Alongside the full-scale pilot testing, our global experts will also be working with water quality modelling, simulating different scenarios to give us knowledge on how to increase treatment efficiency.
Preparing treatment of micropollutants for Oslo Municipality
Though no official requirements have been launched yet, Oslo Municipality is pioneering the initiative, exploring, and planning how to remove micropollutants from wastewater outlets with a new treatment plant. To support this ambition, Ramboll is investigating available on and investigating available technologies on micropollutant removal, and preparing the preliminary design of the plant.
The technologies in question have rarely been used in this context before and Norway has limited recent experience with micropollutant removal. Therefore, Ramboll is working in close collaboration with the Swiss engineering company Holinger in this project, benefitting from their advanced experience with micropollutant removal.
Developing a new method for nitrogen-removal with Søndre Follo WWTP (SFR)
SFR is among the pioneering utilities taking extra steps to contribute to a more sustainable future. Although there are no formal requirements for SFR yet, they aim to initiate efforts that can help protect Oslofjorden in the most sustainable and costs-efficient manner using the latest technologies.
Together with the supplier OxyMem, Ramboll has installed an Aerated Membrane Bioreactor (MABR) pilot at SFR, intended to run for a year. Europe has only a handful of these bioreactors, and this is one of them. It is Ramboll’s responsibility to oversee the whole pilot project, validating the results, and act as advisors. With a positive outcome of this process, a significant decrease in energy consumption is anticipated – potentially only 10% of the regular energy expense for nitrogen-removal.
Exploring centralised nitrogen-removal plant for Oslofjorden
Together with VEAS, Ramboll has led a project to improve the condition of the Oslofjord. Ramboll has been in charge of conducting a feasibility study to consolidate wastewater discharges from all treatment plants along the fjord into a larger treatment plant in the outer Oslofjord at Tofte. The project's conclusion indicates that this solution offers significant socio-economic savings, achieving more than 90% efficiency in nitrogen removal, in addition to removing micropollutants.
Ramboll has initiated further development of the concept to provide a decision-making basis for municipalities to join the project. A concept study will be presented as early as end of May 2025. Ramboll is collaborating with four other companies—Norconsult, Cowi, NIVA, and DHI—to deliver a high-quality product that ensures quality assurance and impartiality in decision-making.
Want to know more?
Tor Håkonsen
Avdelingsleder
+47 97 00 29 10