Sediment Treatment and Environmental Dredging

Worldwide, Envisan is increasingly involved in the various dredging projects of Jan De Nul Group, ranging from permanent maintenance dredging works to land reclamation projects and port extension works.

In cooperation with the dredging division, Envisan develops specific equipment and techniques (both hydraulic and mechanical) to remove sediments from sea or river beds in a highly efficient and environment-friendly manner.

Using very diverse techniques, polluted sediments are either treated on site or in the group's own treatment centres before they are transported to their final destination. The decontaminated sediments can then in most cases be reused as construction materials.

 

Norway, Renere Havn Project Trondheim

Environmental dredging of contaminated sediments from commercial port, ferry terminal and marina; building of confined disposal area in Nyhavn docks; controlled disposal of contaminated sediments...

Environmental dredging of contaminated sediments from commercial port, ferry terminal and marina; building of confined disposal area in Nyhavn docks; controlled disposal of contaminated sediments in underwater cell and confined disposal area; reclamation of a new area of 5,000 m² in the port; capping of area of 380,000 m² with a filter layer and erosion protection layer of (crushed) limestone; 150 m quay reinforcements work (sheet piling).

Key figures
Country

Norway

Client's name

Trondheim Kommune

Contractor's role

Main Contractor

Period

28.03.2015 - 31.05.2016

Technical specs
Equipment

DN18, Hitachi EX1200 Excavator, DN79, Hitachi ZX870, filling system geobags

Scope

Environmental dredging of 65,000 m³ contaminated sediment.
Disposal in underwater cell and confined disposal area.
Building of containment dike around CDA.
Capping of dredged area with rock material (150,000 m³)

Volume

Dredged volume : 75,000 m³ (ipv 65,000 m³)
Dike construction : 130 m (with in the core 7,000 m³ of geobags filled with sediments and/or sand)
Capping : area of 380,000 m² capped with 150,000 m³ of capping material (limestone)

Soil

Mainly silty sand/some areas soft clay

Type of contamination

PCB’s, heavy metals, TBT and PAH

Belgium, Boue B traitement

Dewatering and treatment of contaminated sediments

Dewatering and treatment of contaminated sediments

Key figures
Country

Belgium

Client's name

Public Services Walloon Region

Contractor's role

Joint Venture Partner

Technical specs
Scope

Dewatering and treatment of polluted sediments coming from dredging works of the inland Walloon waterways.
To minimize the transport chain and associated costs, a mobile floating treatment facility was developed that can operate completely autonomously.
The plant enables transport by ship of both incoming sediments and outgoing treated materials.

Methodology

The mobile installation consists of 2 barges. The system, that was entirely developed and designed by Envisan, consists of several modules that can be activated, depending on the type of delivered sediments. On the first barge, sediments are decontaminated by means of techniques as granulometric separation and soil washing. The plant dedicated to the treatment of drained water is situated on the second barge, together with the soil washing installation.
Dredged sediments are transferred directly from the barge or ship into the treatment system. Prior to treatment, the sediments are sieved on 2 sieves to separate aggregates and exogenous materials from the sediments. The sieving and dewatering of sediments takes place on the second barge. Incoming sediments with a dry matter content of 25-30 % are dehydrated with mechanical filter presses. Treated sediments can have a dry matter content up to 70% resulting in a significant volume loss and cost saving on further handling and disposal costs. The average treatment capacity is 1,000 m³ of sediments per day.

Volume

Sediment treatment capacity: 1,000 m³/day
Water treatment facility capacity: 40 m³/hour
Total amount of sediments to be treated within contract: 1,000,000 m³ of which 320,000 m³ by mobile plant

Type of contamination

Heavy metals, mineral oil, organic compounds, PAH's

Tunisia, Taparura Project - Depollution and Rehabilitation Works at the North Coastline of Sfax

Design
Remediation Works: removal of polluted soils Dredging Works in the Kerkannah Channel
Regeneration Works: creation of a new platform and a new beach by reclamation
...

Design
Remediation Works: removal of polluted soils Dredging Works in the Kerkannah Channel
Regeneration Works: creation of a new platform and a new beach by reclamation
Construction of a confined space: 2,300,000 m³ of contaminated soil was stored in a specially designed landfill
Construction of a water management system: pumping system and water treatment
Extension North, Phase II: an extra reclamation of an area of about 900,000 m²

Key figures
Country

Tunisia

Client's name

SEACNVS: Société d’Etudes et d’Aménagement des Côtes Nord de la Ville de Sfax

Contractor's role

Joint Venture Partner (Part JDN-ENV: 70.7%)

Technical specs
Equipment

Trailing Suction Hopper Dredgers Alexander von Humboldt and James Cook
Pontoons DN24 and DN25
Multicats Tabriki and DN49
Land Equipment for civil works

Scope

Remediation & Rehabilitation Works: The Taparura project is one of a series of broader measures taken by the Tunisian authorities to improve the overall environment in Sfax.
Dredging Works in the Kerkannah Channel
Beach Regeneration Works by Reclamation

Soil

Soils to be excavated: sand, sediments, phosphorgypsum
Soils to be dredged and reclaimed: sand

Volume

Dredging Works in the Kerkannah Channel: 6,716,000 m³
Excavation and storage of polluted soils: 2,300,000 m3
Environmental dredging: 700,000 m³
Reclamation: 6,716,000 m³
HDPE-membrane: 35,700 m²

Surfaces

Construction of a landfill: 55 ha
Rehabilitation of a dumpsite (phosphogypsum) > 200 ha
HDPE-membrane: 35,700 m²
Mineral barrier: 35,700 m², with a 60 cm thickness

Dredging depth

10 - 15 m

Coastal Protection

Geotextile: 29,897 m²
Rubble: 1,558 tonnes
Rock Revetment: 61,082 tonnes
Civil works: drainage canals, sewers
Isolation of the phosphogypsum depot by construction of cement bentonite wall & a HDPE-membrane

Belgium, Construction of a Dike to Protect Against Flooding in Vlassenbroek using Dredged Material from the Zeeschelde between Gentbrugge and Melle

The construction of a dike to protect against flooding in Vlassenbroek is the first phase in the construction of a controlled flood plain in Dendermonde. Jan De Nul –...

The construction of a dike to protect against flooding in Vlassenbroek is the first phase in the construction of a controlled flood plain in Dendermonde. Jan De Nul – Envisan elaborated an innovative technique to construct the dike core with engineered sediments. This technique was geotechnically analysed and modelled in detail. Simultaneously, an elaborate test campaign was set up, examining on lab scale the functioning of 20 potential additives in different concentrations. With a selection of additives, pilot studies were also carried out. Based on the results of these studies, a final design was drawn up and then verified by independent design and engineering offices. The sediment comes from the Zeeschelde between Melle and Gentbrugge. It is brought in over water and dumped by means of an ingenious system based on concrete pumps. The additives are added near the site, before the material is inserted in the dike profile.

 

Key figures
Country

Belgium

Client's name

Waterwegen en Zeekanaal

Contractor's role

Main Contractor

Technical specs
Equipment

DN4, DN19, Mixing Plant, Volvo A40, Caterpillar D6

Scope

Construction of a new 800 m long dike to protect against flooding as part of the Flemish Government's Sigma Plan along the river Scheldt whereby 100% of sediments where used for the new dike. The material could not be stockpiled so a batch of dredged sediments was processed and installed within 24h.
The contract consisted of 2 phases (separate contracts):
1. Research and Design:
- Design: execution methods
- Design protection Air Liquide pipeline
- Design dike
- Design berth
- Permits
2. Execution:
- Construction berth and protection pipeline
- Site establishment and access roads
- Dredging of 95,000 m³ in Melle incl. transport to Dendermonde
- Pump works
- Direct installation of sediments

Volume

Sediments: 95,000 m³ (contract: lumpsum for 103,400 m³)
Concrete: 7,400 tonnes

Belgium, Treatment Plant AMORAS

At the end of 2008 an undeveloped and hardly accessible land was located on the Bietenveld site, right bank in the Port of Antwerp. Today, the largest treatment plant for maintenance dredging...

At the end of 2008 an undeveloped and hardly accessible land was located on the Bietenveld site, right bank in the Port of Antwerp. Today, the largest treatment plant for maintenance dredging material in Europe is a fact.

This project has been named AMORAS, an acronym that stands for Antwerp Mechanical Dewatering, Recycling and Application of Silt. With this project the Flemish Government and the Antwerp Port Authority are investing in a sustainable solution for the treatment and storage of the maintenance dredged material from the Port of Antwerp.

The project was awarded to the formed joint venture SeReAnt, in which Envisan takes part. SeReAnt is in charge of the design and construction of the installations and also of the exploitation of the installation during the initial 15-year period.

 

 

Key figures
Country

Belgium

Client's name

Flemish Government - Port Authority Port of Antwerp
Department of mobility and public works

Contractor's role

Lead contractor of Joint Venture (50 %)

Period
January 1, 2009 to January 1, 2026
Technical specs
Scope

Over 1,000,000 m³ of sediments are dredged in the port of Antwerp each year. Jan De Nul Group, as leader of a consortium, designed a sediment treatment plant that significantly reduces the total volume of material to be disposed. Jan De Nul Group is responsible for exploitation and operation of the plant for a period of 15 years.

Methodology

The total volume to be disposed in the specially constructed storage cell is notably smaller than the initial volume of sediments, as usable sands are separated and water is removed out of the sediments
through the various dewatering stages. The dewatering takes place in 4 consolidation ponds of 120,000 m³ each, and through mechanical dewatering by means of 12 filter chamber presses of 21.5 m³ each.

Volume

Sediments treated and dewatered per year: over 2,500,000 m³
Expoitation of the plant: 15 years

Type of contamination

Heavy metals, mineral oil, PAH’s, organic compounds

France, Dredging and environmental remediation in the port of Dunkirk

Over the last 50 years, the closed basins of the Port Autonome of Dunkirk have silted up considerably. Jan De Nul Group and its subsidiary company Envisan designed the dewatering facilities and...

Over the last 50 years, the closed basins of the Port Autonome of Dunkirk have silted up considerably. Jan De Nul Group and its subsidiary company Envisan designed the dewatering facilities and are responsible for dredging and treating of around 60,000 m³ of contaminated sediments per year. All works are being executed inside the port of Dunkirk.

Key figures
Country

France

Client's name

Grand Port Maritime de Dunkerque

Contractor's role

Main Contractor

Technical specs
Scope

Over the last 50 years, the closed basins of the Port Autonome de Dunkerque have silted up considerably due to its hydraulic position. Jan De Nul Group designed the dewatering facilities and is responsible
for dredging and treatment of around 60,000 m³ of contaminated sediments per year.

Methodology

The works are carried out in various stages:
- construction of 3 lagoons of 2 ha each for natural dewatering of the material;
- hydraulic dredging (Trailing Suction Hopper Dredger) of 60,000 m³/year;
- sediment treatment by enhanced natural dewatering in 4 phases:
filling of the lagoons, decantation phase, consolidation phase and forced dehydration;
- handling of the treated sediments;
- re-use and valorisation of the treated sediments.

Volume

Environmental dredging of contaminated sediments: 60,000 m³ / year
Total volume to be dewatered and valorized: 360,000 m³
HDPE-foil: 40,000 m²
Drainage sand: 23,000 m²

Type of Contamination

Heavy metals, mineral oil, PAH’s, organic compounds