Kalundborg, Denmark (RECREATE: since 2024)

Applied technologies

Desalination technologies

Joint control system for two wastewater treatment plants

Rainwater harvesting systems

Ultrafiltration & nanofiltration membranes as pre-treatment for reverse osmosis

Outcome of assessments

Future water strategy modelling using the urban water optioneering tool (UWOT)

The urban water optioneering tool (UWOT) results show that Kalundborg can substantially improve future water-supply security by current conventional sources, Lake Tissø and groundwater, with alternative water resources, particularly seawater desalination, while reclaimed wastewater and harvested runoff provide complementary contributions. Under moderately growing demand (SSP2), supply deficits in 2035 can only be avoided by alternative water resources. Towards 2050 and 2075, additional treatment capacity for seawater desalination and/or wastewater reclamation would be needed. Synergies arise from fit-for-purpose water allocation and from linking planned wastewater-treatment upgrades with future water reclamation, helping to reduce treatment and energy requirements. The overall approach, combining industrial water reuse, multiple water sources and scenario-based modelling, is transferable to other industrial regions seeking more resilient water-supply strategies. More details can be found in RECREATE D1.4.

Quantitative microbial risk assessment: seawater desalination

Seawater desalination is planned in order to provide the industry with drinking water. A quantitative microbial risk assessment (QMRA) was conducted based on very conservative assumptions regarding pathogen concentrations. The results showed that a treatment process consisting of coagulation, flocculation, filtration and a cartridge filter (MF), as well as reverse osmosis and UV disinfection, is required to achieve an acceptable annual infection probability. As rotavirus concentration is the critical parameter, this should be analysed in the intake region of the future seawater desalination plant in order to design an effective, energy-efficient treatment process. Furthermore, technology-specific log removal values should also be used to validate the results. More details can be found in RECREATE D1.3

Quantitative microbial risk assessment: water reclamation

QMRA was used to assess different treatment trains for water reclamation. The exposure scenarios investigated were the inhalation and ingestion of water during car washing, and the inhalation of aerosols from evaporated cooling tower water. The results showed that, for the car washing scenario, a treatment train consisting of ultrafiltration, UV treatment and RO is required if the effluent from quaternary treatment (consisting of ozonation and granular activated carbon filtration) is used.  With a two-stage RO system, failures lasting between 15 and 30 minutes can occur 100 and 10 times per year, respectively, without exceeding the tolerable risk level for annual infection. The next step should be to validate the results using technology-specific log removal values and measured pathogen concentrations instead of default values. More details can be found in RECREATE D1.3

Legislation and policy recommendations

The most important Danish regulations on drinking water and water production are the Danish Act on Water Supply (2020) and the Executive Order on Water Quality and Supervision of Water Supply Installations (2010). The Water Supply Act (2020) focuses on the utilisation and protection of water bodies, their appropriate use, ensuring a satisfactory water supply, and setting quality requirements to protect human health. The Executive Order on Water Quality and Supervision of Water Supply Installations (2010) defines water quality standards for drinking water, requires water quality testing and the monitoring of abstracted water volumes, and supervises water supply systems. Both regulations have been amended recently, allowing for the use of surface water for drinking water production.

The Seawater Executive Order (Havvandsbekendtgørelsen) permits the use of seawater desalination for producing drinking water came into force in December 2025. Furthermore, the production of drinking water by mixing groundwater or surface water with desalinated seawater is also foreseen, as is the use of drilling wells for this purpose.

Another act came into force in July 2025, called the 'Act on Technical Water Supply'. This Act permits the production of technical water from sources other than groundwater, such as treated wastewater or water from polluted groundwater. According to the act, the technical water cannot be used for drinking purposes, but for other uses such as providing feedwater to Power-to-X (PtX) plants. A Power-to-X plant converts surplus renewable electricity into various energy carriers or products. The X can stand for hydrogen for example.

Based on the revised UWWTD (EU 2024/3019), an amendment to the Danish UWWT Act is being prepared. The Danish parliament has agreed to include very strict discharge thresholds for 17 vulnerable areas in Denmark. One of these areas is located at the northern Great Belt near Kalundborg. The currently being discussed thresholds for phosphorus and nitrogen emissions are 0.1 mg P/L and 2.5 mg TN/L, respectively. This is very strict compared to the current discharge thresholds of 1.5 mg P/L and 8 mg N/L. In contrast, the revised EU UWWTD proposes for sensitive areas and especially for WWTPs >150,000 PE, 0.5 mg P/L or 90% removal and 6 mg N/L or 85% removal.

Although the European Water Reuse Regulation (EU 2020/741) has not yet been applied in Denmark, the country is no longer opting out.

See also D1.2 RECREATE (Kleyböcker et al. 2024)