Reviving Oslofjorden: Removal of micropollutants and nitrogen in wastewater

Together with Hollinger and our visionary clients Søndre Follo WWTP (SFR), Vestfjorden Wastewater Treatment Plant (VEAS), Oslo Municipality, Gørvik Municipality, and Vestre Toten Municipality, 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

In 2025, Ramboll finalised a full-scale project at Bekkelaget Wastewater Treatment Plant for improving removal of nitrogen in wastewater. Thanks to this project, the treatment plant now exceeds the requirements of 75% nitrogen removal. Results so far shows that Bekkelaget has managed to reach a treatment level of 80% and removed 1129 tonnes of nitrogen.

The project work entailed mapping of current operations of the plant to optimize management, explore the use of new technologies, and pilot-testing. Alongside the full-scale pilot testing, our global experts also developed a digital model of the treatment process to simulate and evaluate new technologies and other initiatives before implementation.

The project won Ramboll’s sustainability prize in 2025.

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 SFR, Ramboll is working on a project that will prepare and enable the treatment plant for nitrogen removal. As part of that project, we have also supported on an on-going pilot project for an Aerated Membrane Bioreactor. With a positive outcome of this process, the project team anticipates a significant decrease in energy consumption – potentially down to 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.

Following the feasibility study, Ramboll initiated further development of the concept to provide a decision-making basis for municipalities to join the project. In collaboration with Norconsult, Cowi, NIVA, and DHI, Ramboll delivered a high-quality product that ensures quality assurance and impartiality in decision-making.

The project concluded with a concept study in May 2025.

Preparing Rambekk WWTP for new nitrogen-removal requirements

Located north of Oslofjord, Gjøvik and Vestre Toten municipalities are also preparing to meet new regulatory requirements for nitrogen removal – work that will directly affect the health of Oslofjord. To support this work, Ramboll is helping the municipalities develop a joint solution centred on a new biological treatment stage at Rambekk Wastewater Treatment Plant in Gjøvik.

As part of the project, Ramboll is also preparing a cost estimate for a new transfer pipeline from Breiskallen Wastewater Treatment Plant in Vestre Toten to Rambekk, while assessing options for future sludge treatment at Rambekk.

Ramboll’s multidisciplinary team brings together expertise in civil engineering, architecture, technical disciplines, geotechnical engineering, and environmental services. The work will be consolidated in a preliminary design report, providing the municipalities with a robust basis for political decision-making.