Management and Treatment of Organotin and Metal Contaminated Dredged Sediment
Abstract: Today’s society is dependent on international trade and most traded goods are transported by sea. To enable this, regular dredging must be done to maintain water depth in ports and waterways, resulting in the need to handle large quantities of often contaminated sediment. Management options are limited due to regulations and depend on the sediment’s content of contaminants, such as tributyltin (TBT) and metals (e.g. zinc and copper). Consequently, there is a need to investigate new treatment techniques and evaluate the sustainably of management alternatives. In this thesis, several techniques to remove TBT and metal from sediment were developed and tested in laboratory studies, including chemical oxidation by electrolysis and Fenton’s reagent (Fenton) (Paper III), leaching with ultra-pure water, EDDS, saponified tall oil, iron colloids, humic acid, hydroxypropyl cellulose, and acid and alkaline solutions (Paper II). The highest TBT removal from natural sediment was reached using Fenton (64%) followed by electrolysis (58%). On TBT spiked sediment, Fenton and electrolysis reduced the TBT content by 98% by 100% respectively. In spiked water, TBT was degraded 100% by electrolysis. The most effective method for simultaneous TBT and metal removal was Fenton. However, due to the Fenton residue’s low pH, electrolyzed sediment was instead chosen for stabilization and solidification, a method in which a concrete-like product is formed, which could be used in constructions (Paper IV). The electrolysis pretreatment’s impacts on compression strength and leaching patterns were investigated. The results show that stabilized pretreated sediment leached less but had lower compression strength than stabilized untreated samples. The surrounding environment during curing was important, as a saline solution increased the compression strength, decreased TBT leaching, but increased metal leaching compared to a less saline solution. Environmental impacts and costs associated with different sediment management strategies were studied using life cycle assessment (Paper V) and integrated monetary and environmental multicriteria analysis (Paper I). Metal recovery from sediment was identified as a potential future alternative, with increasing metal prices and economic incentives as highly contaminated sediment costs more to handle. However, effective and sustainable metal recovery techniques need to be further developed. The results highlight the importance of individually assessing each site when evaluating risk, determining management strategies, and assessing short- and long-term environmental impacts. The developed methods are useful to identify economic and environmental conflicts and synergetic effects and could be useful tools in decision-making processes. The outcome from this thesis could contribute further to the development of full-scale treatment methods to remediate and enable the use of contaminated sediment.
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