22.09.2020 | Case | Baltic Sea | Sweden
The project demonstrated that dredging and retrieval of sediments from the oxygen-free areas of the Baltic Sea is possible.
Decreasing the internal leakage of phosphorus
TechMarket demonstrated that dredging and retrieval of sediments from the oxygen-free areas of the Baltic Sea is possible. The main aim of the project was to remove the top layers of sediment that consume larger amounts of oxygen. By removing organic substances from the sediment surface, the internal leakage of phosphorus will decrease. Technical tests were carried out in Barnarpa lake, Småland, southern Sweden and deep-sea test waters outside Oxelösund, in the south-eastern part of Sweden.
The project has shown that it is technically feasible:
- to retrieve top layer sediments from deep waters, in this case 120 meters
- to cover large areas of seabed collecting nutrients, with a cost efficient solution at deep waters, in this case some 400 meters wide
- to separate wanted and unwanted fractions (water, mineral silt and organic material) from retrieved sediment
- to obtain drip-free separation of fresh organic sediments without using additives such as polymers
- to rot the organic sediment and produce methane
The organic matter can be used as fertiliser. Low or almost unmeasurable levels of organic pollutants were detected in the sediment in analysis by independent laboratories. Parallel projects confirm that 80% of heavy metals in the sediment can be removed.
The desired outcome of the project is a validation of a test rig for retrieval of sediments from the oxygen-free areas of the Baltic Sea. The conclusions from the test rig will in a second phase dimension a full scale operation at a nominal retrieval pace of 500 tonnes per hour, corresponding to 0.5 tonnes of phosphorus per hour. The test rig design and process should also comply with regulations and requirements of the land based process, such as transportation, depository installations, biogas production, spreading on agricultural soil and leakage to recipient.