Wastewater upgrade reduces phosphorus runoff in Danish Lake District

 

Following heavy rain overloading the combined sewer systems, diluted raw sewage can potentially overflow to nearby lakes, rivers and seas.

Previous solutions have included separating rainwater and sewage, or the establishment of detention ponds, but these require significant investment.

In a move that could reduce phosphorus discharged into the environmentally sensitive “Swan Lake” from stormwater runoff by 90 percent, Danish water utility Skanderborg Forsyningsvirksomhed upgraded an existing wastewater treatment plant.

Clarifier process

Using SUEZ’s Extreme Rate Clarifiers, known as Densadeg XRC for tertiary treatment, the project will serve as the first public global technology reference for this type of application.

A high-rate settling process, the clarifiers use solids contact, ballast addition and solids recirculation to provide enhanced deposition of solids.

The process removes polymer and iron chloride binding phosphorus to solids. Then anthracite is added to ensure a high degree of condensation, which is extracted from the water through lamella separators.

Two lines of Densadeg XRC are used to ensure operation during normal times and during peak flows. Here the utility can experience up to three times normal load, such as during the week of the Skanderborg Festival or extreme rains, which can occur between 10 and 15 times a year.

A video below shows the XRC process:

According to the Skanderborg Utility, the upgrade is “one more step in the direction of intelligent wastewater treatment by shortening the time span between measurement and dosage and increasing the ability to control the load”.

Safe Recreational Lake Waters

As part of a project entitled ‘Safe Recreational Lake Waters’, Denmark previously invested US$710,000 into a strategic collaboration back in 2016.

This involved public and private partners - the Technological Institute, Aalborg University, Stjernholm A/S, Kilian Water, Amphi-Bac and Skanderborg Utility.

One of the primary objectives was to measure the impact of wastewater in the local Skanderborg Lake. Following multiple analyses, tests showed very low concentrations of E. coli in the water caused by overflows.

Furthermore, a multidisciplinary early warning system has been developed for the bathing guests of Lake Skanderborg.

Presented at the Danish Water Forum Annual Conference 2018, the project was funded by the Danish Eco-Innovation Program under the Ministry of Environment and Food of Denmark.

The system evaluates upcoming overflow events and their effect on the bathing water quality; at the same time ensuring treatment of the stormwater before it enters the recipient.

Water technology community interest

Commenting on the wastewater treatment upgrade, Jens F. Bastrup, CEO of Skanderborg Utility and founder of AquaGlobe – Water Solution Center, said: “This project has offered us a good opportunity to showcase our stewardship of the natural environment.”

Per Krøyer Kristensen, CEO of SUEZ in Denmark, added: “Meeting the United Nation’s Sustainable Development Goals has been a high priority for the Danish public. As such, we expect this project to get a significant amount of attention from the water technology community.”

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