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Development of an integrated approach for the removal of tributyltin (TBT) from waterways and harbours: prevention, treatment and reuse of TBT contaminated sediments
www.portofantwerp.be/tbtclean/

More:  Institute 
Reference no: LIFE02 ENV/B/000341
Period: October 2002 till January 2005
Status: Completed

Institute  Top 
  • Gemeentelijk Havenbedrijf Antwerpen (GHA), more, co-ordinator

Abstract:
As one of the largest ports in the world, the Port of Antwerp is particularly affected by TBTcontamination
from ship paints. A LIFE project attempted to remove affected sediments from Antwerp’s harbours and to treat the material for eventual reuse.

The use of tributyltin (TBT) in ship paints has been banned in the EU since the beginning of 2003. TBT is a toxic biocide that was used since the 1970s to prevent the growth of algae, barnacles and other organisms on ships’ hulls. The toxic substance, however, leaches from the paint into marine waters and eventually accumulates in sediments
on the beds of harbours and ports. The removal of these sediments is vital to prevent TBT being reabsorbed into the water.

The project, which was carried out by the Antwerp Port Authority (Gemeentelijk Havenbedrijf Antwerpen), aimed to
demonstrate an integrated approach to the elimination of TBT from the marine environment: prevention, removal,
treatment and finally reuse. Specific objectives included the following:
- Assess the environmental impact of available alternatives for TBT.
- Evaluate the release of TBT from sediments into the aquatic environment during dredging operations.
- Test on a pilot-scale several treatment technologies for TBT contaminated
sediments.
- Identify possibilities for the reuse of treated sediments.

The port teamed up with the Environmental Research Centre (ERC) in Hofstade, (Aalst) to carry out the chemical analyses and perform lab-scale feasibility experiments for the different sediment and water remediation techniques.

Five-point plan:
The project was expected to produce a list of environmentally friendly alternatives to TBT in anti-fouling (that is,
the prevention of growth of organisms) systems. It was also expected to determine limits and best practice
for dredging operations in order to minimise the release of TBT from sediments. To achieve its aims, the project
focused on five main action areas:
1) The drawing up of a questionnaire on alternatives for TBT to be sent to
interested parties in the EU including coating producers, ship-repair yards, ship-owners etc. From the answers received, the project would be able to assess the impact of the alternatives based on their characteristics, active compounds, methods of application, energy use, waste generation and ease of maintenance.
2) Simulation of dredging operations on a pilot-scale and analysis of TBT concentrations in the aqueous phase.
TBT concentrations would be correlated with turbidity measurements taken simultaneously.
3) The dredging of about 2000 m3 of TBT contaminated sediments form the Port of Antwerp and elsewhere in Flanders and its treatment in pilotscale installations, on-site or off-site, using thermal treatment, bioremediation, washing and separation,
phyto-remediation and electrochemical treatment. An evaluation of TBT removal rates for each technique was
to be performed.
4) The construction of a pilot-scale treatment plant for the purification of TBT contaminated waters created during dredging or treatment operations. An evaluation of the removal efficiency of this plant for TBT was planned.
5) The reuse of cleaned sediments in landscaping, dike reinforcement and construction.

Results:

While a standard practice for the reuse or application of sediment on land has yet to be reached, geotechnical
and chemical requirements were developed. Chemical criteria were developed by the Flemish Institute
for Technological Research (VITO) in accordance with Flemish legislation on reuse of soil and treated mineral waste
for construction purposes.

The project provided a general framework for quantifying the effects of toxic materials that can be used in discussions
with the Flemish authorities and for the development of European quality controls on the reuse of sediments.
Some results of the project could also be used to formulate recommendations and restrictions on dredging activities. The project demonstrated that the amount of TBT released during dredging activities is mainly determined by conditions in the harbour (for example acidity, salinity and temperature). These environmental conditions are more important than the dredging technique.

The project also determined that dredging of highly contaminated sediments in the Port of Antwerp is best performed during the winter when the pH of the water is below 8.0. A new time schedule for dredging operations now dramatically reduces the release of TBT in the port. Such a recommendation could also apply to other ports.

Another important aspect of theproject was the construction of a mechanical water extraction installation. The installation should be operational by the end of 2008 and will cost an estimated € 65 million.

The project worked in consultation with the Flemish government to carry out the mechanical extraction of water from dredged material and to develop acceptable TBT-concentrations in dewatered sludge and discharge limits for effluent water.
Dumping sites in Antwerp are expensive and limited in number and size. However, prospects for the port are very encouraging. Once recycled, for example, sediments can now be reused for creating dikes and other constructions.

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