Degradation of organotin in marine sediment
Typ
Examensarbete för masterexamen
Program
Publicerad
2019
Författare
Lointier, Celia
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Tributyltin (TBT) was the main active compound in anti-fouling paints for 40 years and was spread throughout the environment. TBT is toxic for a wide range of aquatic species at low concentrations in water and sediment. With a long half-life time in anoxic conditions, TBT and its metabolites (i.e. dibutyltin, monobutyltin) remain the main contaminants in sediments from many ports and shipyards. Every three to five years, the Port of Gothenburg dredges sediment which is often contaminated by organotin compounds (OTC). As the regulations become stricter for TBT, there is a need for upgrading the management of the dredged material, which is currently mainly deep-sea disposal and landfilling. The degradation of TBT and its metabolites using classic Fenton’s reagent and electrochemical remediation was investigated in this study. Classic Fenton’s reagent and electrochemical degradation were performed on a slurry containing dry sediment mixed in Milli-Q water (L/S≈ 6). The experiments were performed on spiked sediments containing 6800-11200 μg/kg OTC and 1700 μg/kg OTC, and on unspiked polluted sediments from Gothenburg port containing 80 μg/kg OTC.
The results using classic Fenton’s reagent show a degradation up to 96% of the total OTC on the spiked sediments using [H2O2:TOC] = 5; [H2O2:Fe2+] = 15 over 24h for a price of 79 SEK/kg. Tested ratios [H2O2:TOC] = 5; [H2O2:Fe2+] = 5 achieved 94% OTC degradation on the spiked sediments containing 1700 μg/kg OTC; 70% OTC degradation on unspiked sediments; but only 14% degradation on the spiked sediments containing 6800-11200 μg/kg OTC. Classic Fenton’s reagent would thus be a good method for old sediments but demonstrates its inefficiency on sediments recently polluted with extremely high concentrations. Electrochemical remediation achieved an OTC removal of ~100% on the spiked sediments containing 6800-11200 μg/kg OTC over 24h using Nb/BDD electrode at the anode and titanium at the cathode with a current density was 7 mA/cm². The electricity consumption was 0.092 kWh/kg corresponding to a cost of 4.8 SEK/kg. . On the other hand, the concentrations in the liquid phase was extremely high and the method needs to be further developed to also include a step for degradation OTC in the liquid followed by metal extraction. The spiked sediments post electrochemical remediation could be dumped at a deep-sea storage site without restrictions in 7 out of 8 countries, whereas it may not be possible to dump them after Fenton’s degradation. Electrochemical remediation seems to be a possible solution for managing sediment from the port of Gothenburg if the method can be further developed to more effectively degrade the OTC in the liquid phase after the electrolysis.
Beskrivning
Ämne/nyckelord
remediation , marine sediments , port , organotin , tributyltin (TBT) , dibutyltin (DBT) , monobutyltin (MBT) , classic Fenton’s reagent , electrochemical degradation