Sediment and Sludge Treatment

AMORAS (Antwerp, Belgium)

The Need

Guaranteeing sufficient draught to shipping traffic is an essential condition for the Port of Antwerp to prosper now and in the future. In order to do so, the Antwerp Port Authorities need to dredge and store large volumes of siltation material on annual basis. However, the available deposit areas for dredged spoil are insufficient.

The Flemish Government, therefore, has decided to build a mechanical silt dewatering plant in the port area as a lasting and innovative solution for the treatment and storage of dredged spoil. This ambitious project has been given the name AMORAS.

The Solution

The acronym A.M.O.R.A.S. stands for “Antwerpse Mechanische Ontwatering, Recyclage en Applicatie van Slib” (Antwerp Mechanical Dewatering, Recycling and Application of Silt). The project shall provide a permanent solution for recycling and storage of dredged sediments in the port of Antwerp.

AMORAS will be implemented in two phases.

• Phase 1 will cover detailed engineering and construction of the dewatering plant and will be executed in a period of 30 months.
• In phase 2 the actual exploitation of the plant will start for a period of 15 years. Calculated in ‘dry material’ some 500,000 tonnes will have to be treated and storage on annual basis.

The partners taking part in the SeReAnt joint venture company have extensive and specialised experience with all distinctive aspects of the AMORAS project, such as the exploitation of various silt treatment centres, dredging and transport of dredged spoil, desanding and mechanical dewatering including storage of dredged spoil. Moreover, these companies can count upon a substantial in-house diversified environmental expertise.

In terms of sustainability the proposed silt dewatering installation meets all contemporary ecological demands, pursuing maximum efficiency of used energy in every phase of the process applied.

Moreover, the plant has a reliable and user-friendly design as a result of far-reaching automation, in-depth control systems and optimal use of available capacity, allowing SeReAnt to guarantee a very long life cycle for the AMORAS project.

The Works

The attached drawing shows the seven important steps in the AMORAS project:

1. Underwater cell
the maintenance dredging material from the harbour docks is stocked temporarily by the Antwerp Port Authority in an underwater cell (capacity 150,000 m³) to be created in the Canal Dock B1. A dredging unit pumps the dredged spoil to the shore for the treatment process to start. More or less heavily contaminated spoil is not stocked temporarily but pumped ashore directly using a barge unloading dredger.

2. Sand separation
The material pumped ashore is diverted to a sieving installation to remove all coarse elements. Depending on the environmental quality of the material and/or the detected sand fraction percentage, the decision is taken to de-sand the material in a sand separation plant.

3. Discharge line
Next, the material is pumped through a discharge pipeline to the treatment plant on the Bietenveld, 4 kms away.

4. Consolidation ponds
On the Bietenveld site the material is deposited temporarily in 4 consolidation ponds, having a capacity of 120,000 m³ each. In the consolidation ponds, the process water required for sieving, de-sanding and pumping of the material is separated again. Less contaminated spoil is deposited in three consolidation ponds, whereas more contaminated material goes to the fourth pond.
An innovative dredging system with rotating gantry spanning the consolidation ponds allows fully automated steering of the process. The dredging gantry is equipped with two mobile dredge pumps that can move along the entire span and that are able to work independently from each other.

5. Dewatering plant using filter presses
In the dewatering hall the consolidated spoil is conditioned and dewatered to form a residue of filter cakes. A number of membrane chamber filter presses dewater the material, pressing the water through a filter cloth.

6. Water purification plant
The filter process water and other effluent water is gathered in the buffer pond for waste water and subsequently pumped to a water purification plant. There the particles in suspension are removed through a physico-chemical process. In a second step the organic material and nitrogen is removed by means of biological cleaning.

7. Deposit site
The controlled deposit of the filter cakes is located on the site “Zandwinningsput”, situated between Hooge Maey, Indaver and the A12 motorway. On this site a stack of filter cakes, over 50 m high, can be deposited on top of an existing 10 m layer of medium consolidated silt that has been deposited there earlier.