Improved protection of lakes in Skanderborg

Denmark’s most sensitive in-land aquatic environment is called “Søhøjlandet”. To control eutrophication in these water areas, there is a strong focus on the phosphorus content discharged from the wastewater treatment plants.
Our mission

Improve phosphorus removal to ensure protection of the local fresh waters of Søhøjlandet

Skanderborg is located in one of Denmark’s most sensitive in-land aquatic environments, “Søhøjlandet”. The area is under protection and there is a need to comply with regulations about phosphorus discharge from wastewater treatment plants to the lakes. Phosphorus concentration of the discharged wastewater must therefore be decreased to comply with the strict outlet requirement.
Additionally, Skanderborg municipality expects population and industrial growth in the future combined with a centralization of their wastewater treatment plants.

In this case the wastewater treatment plant in Skanderborg was upgraded with SUEZ’ technology – Densadeg XRC™ - extreme rate clarifier.

It targets wastewater treatment plant effluents as well as the stormwater overflows (known as CSO) leading to discharge of untreated wastewater combined with sewer flows when exceeding the hydraulic capacity of the sewer and/or wastewater treatment plant.
Our solution

A unique combination of solids contact, ballast addition and solids recirculation providing enhanced, rapid wastewater treatment for tertiary phosphorus removal and CSO application

Wastewater treatment plant in Skanderborg is subjected to phosphorous discharge requirement of 1,38 kg/day to Skanderborg Lake, which is equivalent to 0,265 mg/L in the effluent with the current discharge of 1.900.000 m3/year.

Skanderborg municipality expects population and industrial growth in the future combined with a centralization of their wastewater plants. The phosphorus concentration of the discharged wastewater must therefore be decreased to an average level below 0,15 mg/L to comply with the outlet requirement.

In this case wastewater treatment in Skanderborg upgraded the plant with SUEZ technology – Densadeg XRC™ - extreme rate clarifier.
About the technology
Densadeg XRC™ is a high-rate settling clarifier process combining solids contact, ballast addition (dense granular additive) and solids recirculation to enhance settling of solids, which results in rapid floc maturation and faster clarification.

The process consists of:

  1. rapid mix / coagulation stage
  2. flocculation zone
  3. maturation zone
  4. settling & clarification zone
  5. hydrocyclone and ballast recovery
  6. effluent collection


This video shows how our technology works:

Densadeg XRC™ extreme-rate clarifier

Credit: SUEZ - Water Technologies & Solutions

Our results

Installation of Densadeg XRC™ in Skanderborg is our first global reference, where we combined tertiary and CSO treatment

We carried out a monitoring program from March to September 2020 to assess the operating capacity of the Densadeg XRC™.

These first months of operation as tertiary treatment showed:

  • average outlet levels:
    - 0,11 mg/L for total phosphorus
    - 3 mg/L for suspended solids
  • with an iron chloride dosage ranging from 35 to 55 mg/L
  • proven lamellar velocity up to 100 m/h

A significant decrease has been demonstrated between the outlet total phosphorus concentration before the construction of the Densadeg XRC (0,30 mg/L on average) and since it has been in operation (0,11 mg/L on average).

Our data enabled us to estimate that the Densadeg XRC™ operation as tertiary treatment could remove additional 584 kg of phosphorus per year!

Densadeg XRC in Skanderborg

Credit: SUEZ Water Denmark

Contact us

Contact our expert

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