Management and Treatment of Organotin and Metal Contaminated Dredged Sediment

Doctoral thesis, 2021

Modern 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 large quantities of often contaminated sediment that must be handled. Management options are limited due to regulations and depend on the content of contaminants such as tributyltin (TBT) and metals (e.g., zinc and copper) in the sediment. Consequently, there is a need to investigate new treatment techniques and evaluate the sustainability 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 low pH of Fenton residue, electrolyzed sediment was instead chosen for stabilization and solidification, a method that forms a concrete-like product that could be used in construction (Paper IV). The impacts of electrolysis pre-treatment on compression strength and leaching patterns were investigated. The results show that stabilized pre-treated 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 and 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 sediments cost 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 for identifying economic and environmental conflicts and synergetic effects and could be useful tools in decision-making processes. The results of this thesis could contribute further to the development of full-scale treatment methods to remediate and enable the use of contaminated dredged sediment.