Full scale thermal treatment of highly tri-butyltin (TBT) contaminated sediments.
Type:
Presented during:
CEDA Dredging Days 2005 - Dredging: The Extremes, Rotterdam
Authors:
Pieters A., Goethals L.M.J.G. and Pynaert K.
Abstract: During recent decades, tri-butyltin (TBT) has frequently been used as an anti-fouling agent in ship paints. Because of the slow release from the ship hulls and its strong tendency to adsorb onto sediments, TBT is detected in significant concentrations in sediments along busy maritime traffic routes and in port and harbour docks.
From a toxicological point of view, TBT is a very harmful chemical because of its potential biocidal properties and adverse affects on non-target organisms. Therefore a world-wide ban has been placed on the use of TBT in ship paints and on the relocation dredged material, contaminated with TBT in open sea. 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 is equally important.
Because of the chemical properties of tri-butyltin (TBT), i.e. the high volatility and relatively low boiling 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 the organotins to inorganic tin. For low TBT contaminated sediments, bio-remediation proved to be a satisfactory remediation technique, however for the highly TBT contaminated sediments (> 6 mg TBT/kg DW), thermal treatment proved to be the only feasible remediation technique, with a high removal efficiency.
In June 2004, full scale thermal treatment has been performed in Envisan’s soil treatment centre at Gent (Belgium). The TBT-contaminated sediment, up to 72 mg TBT/kg DM, has been treated in the semi-mobile ‘thermal desorption unit’ at four different temperatures, i.e. 300, 350, 400 and 450°C and off gases were monitored. At 450°C, a clean up efficiency of 99,5 % was achieved. At this temperature, also mineral oil was completely removed and the clean up efficiency for Poly Aromatic Hydrocarbons was above 98%.
Keywords : TBT-contaminated sediment, thermal treatment, stepwise debutylation