Environmental management aspects for TBT antifouling wastes from the shipyards

Tributyltin (TBT)-based antifouling paints have been successfully used for over 40 years to protect a ship's hull from biofouling. However, due to its high toxicity to marine organisms, the International Maritime Organization (IMO), in 1990, adopted a resolution recommending governments to adopt measures to eliminate antifouling paints containing TBT. High concentrations of TBT are detected in the vicinity of ports and shipyards. TBT is also usually detected in the sediment, in which it accumulates. This study reviews recent literature for the best management practices (BMPs) in order to minimize the environmental effects of TBT. The paper focuses on the evaluation of the available techniques for the removal of TBT from shipyard wastes and from the sediment. The most effective treatment methods are highlighted. BMPs include recycling of abrasive materials, use of cleaner abrasive materials, reuse of spent abrasive materials, substitution of hydroblasting by vacuum blasting or containment or ultra-high-pressure water blasting and confinement of pollution by enclosure and containment systems. The treatment of the TBT wastes by conventional biological wastewater treatment processes is probably not suitable, because the concentrations of TBT found in shipyards' wastewaters are toxic to microorganisms. Advanced technologies such as activated carbon adsorption and dissolved air flotation, in combination with filtration and coagulation-clarification, photodegradation and electrochemical treatment, are required to remove TBT. However, advanced methods should be further optimized to meet the regulatory limit of 200 ng/L. To date, only one published work examines the efficiency of incineration for the treatment of solid sandblast wastes. Regarding the treatment of sediment, land deposition of the less polluted fraction of sediment is a feasible option. Such treatment must take into account the risk of contamination of groundwater and the surroundings, and it requires extended areas of land. Other treatment methods, such as thermal and electrochemical treatment, are promising options but due to the large amounts of dredged material, they have high capital and operational costs.