The Flemish government, Port of Antwerp and contractor SeReAnt will start this month with the dredging and processing of the most heavily polluted dredged spoil in the port, the so-called TBT sludge. "After years of research, there is now finally a solution to this historical pollution. This is a worldwide first and a milestone for Flanders and the port of Antwerp”, says Lydia Peeters, Flemish Minister of Mobility and Public Works. "We will remove the most heavily polluted sludge from the port. This will improve the water quality substantially.”
Pollution by shipyard
The Flemish government and Port of Antwerp jointly keep the docks of the port of Antwerp accessible for today’s ships. Every year, enormous quantities of sludge are dredged for this purpose and then processed by the AMORAS dewatering plant. "One type of sludge could not yet be treated: sludge with elevated organotin concentrations or Tributyltin, TBT sludge for short”, says Yi-Bin Shan, Head of the Maritime Access Department of the Mobility and Public Works Ministry. "TBT was used worldwide in ship paint since the 1970s to prevent the accumulation of mussels and algae on hulls, but has been completely banned since 2003. The product is extremely harmful to the environment and is also difficult to break down. The sludge has been storing TBT like a sponge all these years and is gradually releasing the contamination. In this way, it disturbs the metabolism and hormone balance of mainly shellfish, such as mussels and snails."
Only port in the world
"Together with the University of Antwerp, we have been examining for several years how to get TBT out of the port”, says Jacques Vandermeiren, CEO of Port of Antwerp. “We are proud that we are now finally able to tackle this historical pollution. Currently, the water quality in the docks scores below the European standard. With this project, the quality will strongly improve. As a port authority, we believe it is important to take responsibility towards society. We are the only port in the world that not only removes polluted sludge, but also ensures its sustainable treatment.” The Flemish government and Port of Antwerp make the necessary resources available for the dredging and processing of the most heavily polluted dredged spoil. “Flanders provides 25 million euros annually for the exploitation of AMORAS. We are now making an additional investment of 700,000 euro a year to dispose of TBT-sludge in an ecologically responsible manner. In this way, we increase the accessibility of the port, an important task of the Flemish government”, says Flemish Minister Lydia Peeters.
“Port of Antwerp has invested 1 million euro in the preliminary phase of this project and will spend another 1.5 million euro per year for the effective treatment of TBT sludge”, port alderman Annick De Ridder continues. “Port of Antwerp wants to be an inspiration for other ports and take a pioneering role in the field of sustainability.”
800.000 m³ of sludge over the next five years
Processing the total quantity of polluted sludge in the port of Antwerp will be a long-term assignment. A pilot project was started in 2018 after having obtained the necessary permits and after having made some modifications to the water treatment plant. "We have added an extra step in our processes and installed activated carbon filters. They filter the toxic substances out of the water after they have passed across our treatment plant”, explains Yi-Bin Shan, Head of the Maritime Access Department. "During this pilot project, we already dredged, transferred and treated 185,000 m³ of heavily contaminated sludge in the AMORAS plant. This has enabled us to properly map out the impact on the plant as well as all potential risks. Now, there is an agreement to remove 800,000 m³ of sludge from the docks over the next five years and to process it into 500,000 tonnes of filter cakes. We will first remove the sludge obstructing the nautical access and the worst TBT hotspots in the older, southern part of the port. After this, we will take on the other port areas.”
How do we proceed?
- The contaminated TBT sludge is dredged from the docks. With a 15 m³ eco-friendly gripper, we avoid spreading the pollution to the surrounding water.
- The dredged spoil is transported to the AMORAS treatment plant in transport containers of 2400 m³.
- SeReAnt, the contractor operating the AMORAS plant, extracts the sludge from the transport containers and pumps it into the treatment plant.
- Coarse dirt and sand are removed.
- The waste water is purified via a water treatment plant and then led back to the docks. TBT sludge is also purified by activated carbon. The water then flows back to the docks.
- The sludge is processed into a dry end product: filter cakes that are safely stored on site.
AMORAS: innovative collaboration between government, port and dredging companies
Through AMORAS, the Flemish government and Port of Antwerp are working together on the sustainable and long-term storage and treatment of dredged spoil from maintenance dredging works in the Antwerp docks. AMORAS stands for ‘Antwerpse Mechanische Ontwatering, Recyclage en Applicatie van Slib’ (Antwerp Mechanical Dewatering, Recycling and Application of Sludge). The Mobility and Public Works Ministry is responsible for 80% of the funds, Port of Antwerp for the other 20%. Since 2011, the dewatering plant annually processes 450,000 tonnes of dry matter into filter cakes. The Temporary Trade Association SeReAnt operates the plant. SeReAnt is a partnership between the environmental companies DEC of DEME Group and Envisan of Jan De Nul Group. AMORAS is constantly looking for solutions to reuse the dry matter obtained from non-polluted dewatered sludge in useful applications. Several options are being explored, but especially the concrete industry shows interest in the filter cakes.