Industry News
2026-10-15Ramboll is working with Norwegian municipal authorities and water utilities to advance 5 wastewater treatment projects, with the goal of improving the ecological condition of the Oslofjord. Among them, the nitrogen removal rate at the Bekkelaget wastewater treatment plant has exceeded the legal requirement of 75%, reaching 80%, with cumulative nitrogen removal of 1129 tons; if the aerated Membrane Bioreactor pilot at Søndre Follo succeeds, nitrogen removal energy consumption is expected to drop to 10% of conventional levels; the Tofte centralized treatment scheme is assessed to achieve a nitrogen removal efficiency exceeding 90%.
I. An Ecological Alarm for a Fjord
The condition of the Oslofjord has continued to deteriorate in recent years. Years of nutrient pollution have caused a severe decline in dissolved oxygen in the fjord, fish populations have nearly collapsed, the lower limit of seaweed growth has continued to shift downward, and algal blooms and slime are encroaching on the living space of other organisms. The latest fjord condition assessment released by the Norwegian Institute for Water Research further confirms this trend.
Ellen Hambro, Environmental Director at the Norwegian Environment Agency, provided a set of key figures: nitrogen from sewage and agriculture together accounts for approximately 75% of the nitrogen load entering the Oslofjord. This also explains why all parties have focused their attention on the wastewater treatment side — the treatment cycle for agricultural non-point sources is long, while wastewater plant discharges are relatively concentrated and controllable, and there are mature technical pathways for upgrading standards.
A more direct driving force comes from regulation. Norwegian municipalities and operators are preparing for stricter EU wastewater discharge rules, and the new rules impose higher requirements on discharge volumes and acceptable levels of nitrogen and micropollutants.
II. Bekkelaget: From 75% to 80%, Digital Models First
Ramboll completed the full-scale nitrogen removal upgrade of the Bekkelaget wastewater treatment plant in 2025年. The operating results are: the nitrogen removal rate exceeds the legal requirement of 75%, reaching 80%, with cumulative nitrogen removal of 1129 tons.
What is noteworthy is not the 5 percentage point improvement itself, but the way it was achieved. The project did not directly install new equipment, but first conducted a round of systematic diagnosis: reviewing existing operating conditions, improving management strategies, evaluating new technologies, and conducting pilot tests. On this basis, Ramboll experts developed a digital model of the treatment process, simulating and comparing various possible improvements before implementation.
This pathway has general reference value for upgrading existing plants. The nitrogen removal potential of most wastewater plants is not entirely limited by the capacity of the structures themselves; the optimization space for operating parameters such as dissolved oxygen control, reflux ratio, carbon source dosing points, and sludge age is often underestimated. Using digital models to screen first can avoid spending investment on the links with the lowest marginal benefits. The project received Ramboll's 2025年 sustainability award.
III. Søndre Follo: Aerated Membrane Bioreactor, Nitrogen Removal Energy Consumption May Drop to One-Tenth
At Søndre Follo, the project team is piloting an aerated Membrane Bioreactor (AeMBR). The concept of this technical route is to change the method of membrane fouling control: conventional Membrane Bioreactors rely on high-intensity aeration to scour the membrane surface to delay fouling, and aeration energy consumption typically accounts for the largest share of membrane system energy consumption; the aerated Membrane Bioreactor, by contrast, attempts to maintain flux at lower aeration intensity.
The project team expects that if the trial succeeds, the energy consumption of the nitrogen removal stage is expected to drop to 10% of conventional levels. It should be noted that this is an expected value at the pilot stage and still requires long-term verification under actual influent conditions. But the direction itself is clear: bringing down nitrogen removal energy consumption is a common challenge for Europe's next round of standards upgrading.
IV. Tofte: The Feasibility Calculation for Centralized Treatment
Unlike single-point upgrades, the Tofte scheme proposes the concept of a centralized treatment facility. The conclusion of the feasibility study is that the scheme has significant socioeconomic benefits, with nitrogen removal efficiency capable of exceeding 90%, while also having micropollutant removal capability.
The logic of centralized treatment lies in economies of scale. If multiple small wastewater plants each install their own set of advanced treatment and micropollutant removal facilities, both unit investment and operation and maintenance costs are very high; if wastewater can be collected through pipelines to a single centralized facility, a more complete process combination can be adopted, and it is also easier to afford the ozone, activated carbon, or advanced oxidation units required for quaternary treatment (micropollutant removal). The trade-off is water conveyance energy consumption and pipeline investment, which need to be calculated on a case-by-case basis.
V. Micropollutants: The Next Threshold
A considerable proportion of these five projects point to micropollutants, and most are at the research or planning stage rather than already built and operating. The Oslo municipal authorities are studying how new treatment plants can remove micropollutants from wastewater discharges — even though formal requirements have not yet been issued.
This "research first, mandate later" rhythm is representative of Europe. Micropollutants (pharmaceutical residues, personal care product ingredients, PFAS, microplastics, etc.) have limited removal rates in conventional secondary treatment, and their removal requires additional advanced treatment units, with considerable investment and energy consumption. Regulators typically push forward feasibility studies and technology reserves first, and set limits only after the cost curve and monitoring methods mature. For operators, planning ahead is far more proactive than reacting passively.
VI. Reference Significance for Domestic Upgrading and Retrofitting
Although the geographical conditions of the fjord differ from those of China, three lessons are universally applicable:
- For nitrogen removal upgrading, calculate the operational account first, then the engineering account—Bekkelaget's experience shows that process diagnosis and digital simulation carried out first can often achieve considerable efficiency improvements with relatively small investment, avoiding blind capacity expansion.
- Energy consumption determines the sustainability of upgrading—From the Aerobic Membrane Bioreactor to centralized treatment, the common direction of European technology routes is to reduce the energy consumption per unit of nitrogen removal. Against the backdrop of continuously tightening Total Nitrogen limits in China, the value of low-energy nitrogen removal processes (such as process routes that enhance internal carbon source utilization) is likewise rising.
- Micropollutants should be incorporated into planning reserves in advance—If the land footprint, energy consumption, and interfaces of quaternary treatment units are reserved during the new construction or retrofit stage, the cost is far lower than adding them later.
The five projects in the Oslofjord vary in scale and are at different stages, with some completed and others still on paper. But together they outline a clear path: from single-point compliance to watershed goal orientation, and from end-of-pipe removal to equal emphasis on energy consumption and efficiency. This transformation deserves the attention of all markets that are advancing upgrading and retrofitting.
TIANYI TECH Co., Ltd. (TIANYI LIMITED) has long been deeply engaged in the fields of wastewater treatment and Reclaimed Water Reuse. Centering on the three major directions of low-carbon processes, resource recovery, and smart operations, it provides full-chain services from solution design, equipment manufacturing, and engineering construction to operation management for municipal wastewater plants, Industrial Parks, and various water-using entities. With the goals of "stable compliance, energy saving and consumption reduction, and resource circulation," the company continues to help customers reduce operating costs and enhance system resilience in the green and low-carbon transition.
Source: Compiled from the progress report on Oslofjord wastewater treatment projects released by Ramboll on 2026年10月12日, and public statements by the Norwegian Environment Agency and the Norwegian Institute for Water Research.
