SGI tests new dredging method for contaminated fibre sediments
Dredging of contaminated bottom sediments can release hazardous substances into the water. However, a new method is now being tested to reduce this risk. At the same time, the volume of material that needs dewatering is reduced. The Swedish Geotechnical Institute (SGI) and the Municipality of Sundsvall are conducting trials to handle contaminated fibrebanks more efficiently and gently, using the so-called CDS method.
The method is being tested for the first time at the site of the former Essvik paper mill in Sundsvall. At numerous locations in Sweden, former paper and sawmills have left behind fibrebanks on seabeds and lakebeds. These banks often contain high levels of pollutants that can spread into surrounding waters. As the fibres degrade, they also produce gas, which may contribute to the greenhouse effect. There is therefore a strong need for effective remediation methods.
How the CDS method works
Traditional dredging can stir up sediments, allowing contaminants to disperse in the water. The CDS method (Contained Dredging System) involves suctioning sediment into a large air-filled chamber, which reduces turbidity and the spread of pollution. The method also decreases the amount of dredged material that needs to be dewatered – a clear environmental benefit that also saves both time and money.
Testing the method under real conditions
The CDS method has previously shown promising results on sandy sediments, but it has not yet been tested on fine-grained, fibre-rich sediments or fibrebanks.
The current project aims to test and adapt the CDS method for these challenging conditions. The equipment will be trialled in a real-world setting, and SGI will evaluate the method’s effect on contaminant spread and the characteristics of the dredged material.
“We’re very pleased to receive the funding that makes this pilot project in Essvik possible. It’s a step towards improving our marine environment on a larger scale and using the method more widely,” says Sven-Åke Westman, project manager at Sundsvall Municipality.
Goal: more efficient remediation
SGI has been granted SEK 7 million by the Swedish Environmental Protection Agency for its part of the project, which will run from 2025 to 2029. In the first year, a feasibility study will be carried out to map the current sediments and fibrebanks.
“By adapting the CDS method, we hope to develop a more efficient and gentle approach to remediating contaminated sediments – especially fibrebanks. The goal is to create a method that can be used for sediment remediation both in Sweden and internationally,” says Ann-Sofie Wernersson, ecotoxicology researcher at SGI.