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Katrineholm municipality

Low-flow dredging improves water quality in the Ouljar.

The customer's challenge

Eutrophication due to internal loading

Öljaren, a lake in the municipality of Katrineholm, has had problems with eutrophication for a long time, resulting in excessive algal blooms, deteriorating water quality and periodic fish kills.

As part of its participation in the LIFE IP Rich Waters project, the municipality is evaluating the method of low-flow dredging to improve the lake’s water quality and the effect of reintroducing nutrients through uptake and sedimentation to agricultural land.

Sjön Öljaren utanför Katrineholm.
Bild: Josefine Karlsson / Katrineholms kommun
Clean reject water is returned to the lake after being filtered through a sand filter.
Our solution

Low-flow dredging with a specially built pontoon

Low flow dredging is an innovative technique where Tecomatic has designed a unique pontoon to meet the specific challenges faced by the customer. In addition, we have continuously developed the method to improve the uptake of the sediment.

In low-flow dredging, an electrically powered pontoon sucks up the top layer of nutrient-rich sediment on the lake bed. The sediment is then pumped in a hose up to a polymer station where polymer is added to flocculate the sediment. It is then pumped to a dewatering bag similar to a coffee filter where the particles (nutrient-rich sediment) remain in the bag and the lake water flows out. Before the water is returned to the oiler, it is pumped through a sand filter which filters the water once more.

The sediment left in the bag is so clean and contains, among other things, nutrient-rich phosphorus and will be returned to our cycle by being used as fertilizer on arable land.

Facts and figures

Skylt som visar texten: Här pågår lågflödesmuddring för en bättre miljö.
Katrineholm municipality has had several study visits as many are interested in the project.

“We have been working with Tecomatic since 2020 and we have been able to develop our work together on this project. The method of low-flow dredging a lake and the circular tank is new, so we have had to try out a solution that works well. Working in a lake with strong winds has been one of the challenges that Tecomatic has had to handle and modify the equipment for. The project has been instructive for both parties and we look forward to the continued work.”

– Jenny Herbertsson, environmental strategist, Katrineholm municipality

Katrineholm municipality is participating in the unique LIFE IP Rich Waters project, which is a collaboration between authorities, municipalities, companies, researchers and water conservation associations and is part of the European Commission’s environmental program. By providing new knowledge and better methods, the project will tackle some of the most serious environmental problems affecting the quality and vitality of water.

Read more about the project on the Katrineholm municipality website.

Or on the Rich Waters website.

Watch the LIFE IP Rich Waters movie.

Listen to the P4 Sörmland report on the project.

The low flow dredging process

Tecomatic’s low-flow dredging method is gentle on bottom fauna and aquatic organisms as only the top layers of sediment are sucked up. This is particularly important in environments where we want to minimize turbidity and avoid disturbing marine life.

En bemannad eldriven

A manned electric pontoon sucks up sediment from the bottom. The operation and water level of the dam is not affected.

Sedimentet pumpas

The sediment is pumped via a hose up to a control station where polymer is added. The sediment is then pumped to a geotube.

Illustration på en geotub och ett sandfilter.

The sediment is dewatered in the geotube and the reject water is pumped to a sand filter container. The sand filter purifies the water from smaller particles and returns to the lake as clean water.

Illustration som visar en traktor lastad med sediment.

What remains in the geotube are nutrient-rich sediments that contain, among other things, phosphorus. These can be used as fertilizer in agriculture.

Contact us

Mikael Strand

Water treatment project manager

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