Sustainable management of dredged sediments : potential recovery of valuable compounds

Dredging of sediments occurs worldwide to increase water depth in harbours, bays, lakes and rivers, as well as to recover aquatic ecosystems. Landfilling and open-ocean discharge are traditional disposal routes for dredged material. However, the methods are restricted by environmental and legal concerns. Using dredged sediments for beneficial uses can contribute to implementing circular economies and avoiding traditional disposal methods. This thesis aimed to contribute to the sustainable management of dredged sediments by increasing the knowledge of the beneficial use of the material. The work focused on Malmfjärden bay, located in Kalmar, Sweden, which is currently shallow and presents a high concentration of nutrients. The LIFE SURE project aimed to dredge the bay and use the dredged material for beneficial purposes. The results from the thesis showed a high potential to use Malmfjärden sediments for beneficial uses. The first step involved the characterisation of sediments, which showed a medium-high content of N and P was also present. The main pollution concerns were As, Pb and Cd, since their contents overpassed the Swedish limits for sensitive uses. The speciation and extraction of elements were also performed to assess their risk of pollution. The results showed that the most labile elements were Zn and Pb, and both presented the highest extraction rates using EDTA and EDDS. The results showed that the chemical extraction of metals could contribute to treating metal-polluted sediments and become a mining technique. Further studies focused on the recovery of nutrients from the sediments. They were mixed with compost, and lettuce grew in different substrates. However, the plants prematurely stopped growing, possibly due to the lack of available forms of N. Moreover, the harvested lettuces overpassed permissible contents for Cd, slightly threatening human health. It was shown that dredging could provide nutrients to soils, but the risk of metal pollution should be assessed. Finally, a life cycle assessment was calculated to assess the environmental impacts associated with landfilling Malmfjärden sediments or using the material in soil conditioning. Both scenarios presented negative impacts on global warming, eutrophication and toxicity categories. However, soil conditioning showed the most positive score due to the environmental savings of avoiding the production and use of fertilisers. The thesis concludes by encouraging the performance of more interdisciplinary projects. This could combine the knowledge from several sectors to enhance the implementation of the beneficial use of dredged sediments.