Remediation of Tri-butyltin (TBT) contaminated sediments by means of a thermal treatment
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
L. Goethals, I. Janssens, and G. Ide
Abstract: During recent last decades, tri-butyltin (TBT) has frequently been used as an anti-foulingagent in ship paints. Because of the slow release from the ship hulls and its strong tendency to adsorbonto sediments, TBT is detected in significant concentrations in sediments along busy maritime trafficroutes and in port and harbour docks.
From a toxicological point of view, TBT is a very harmful chemical because of its potential biocidalproperties and adverse affects on non-target organisms. Therefore a world-wide ban has been placed onthe use of TBT in ship paints and on the relocation dredged material, contaminated with TBT in opensea. Since 1st of January 2003, this prohibition has seriously affected highly industrialised ports.
In addition to the stringent legislation on the primary release via TBT containing anti-fouling paints,the development of an effective remediation method to treat historically contaminated sediment isequally important. Within the framework of an EU project (TBT CLEAN LIFE02 ENV/B/000341),various sediment remediation techniques are being examined.
Because of the chemical properties of tri-butyltin (TBT), i.e. the high volatility and relatively lowboiling point (170°C), thermal treatment was considered as one of the possible remediation techniques.
Lab-scale tests at high temperatures, showed stepwise debutylation and complete degradation of theorganotins to inorganic tin.
However, when a thermal treatment is considered, the water content of the input material is a limitingand cost determining factor, because of the sediment handling in the desorption unit and the heatnecessity for water vaporisation. Lab-scale tests have shown that sediment dewatering in advance canoptimise the thermal treatment. In this case complete degradation of the organotins was achievedwithin less then 10 minutes for very highly contaminated sediment.
Keywords: TBT contaminated sediments, thermal treatment, stepwise debutylation, sedimentdewatering