Applying Multivariate Analysis to Developing Electrodialytic Remediation of Harbour Sediments from Arctic Locations

Abstract

Electrodialytic remediation (EDR) is a method for removing pollutants from different materials achieved by acidification and transport processes induced by application of an electric field of low intensity. In the thesis, EDR was shown to be a reliable technology for removal of heavy metals, PAH, PCB and TBT from harbour sediments. The final concentrations of heavy metals met the background criteria (non-polluted) as defined by OSPAR, while further optimisation of EDR is necessary for achieving similar levels of PAH, PCB and TBT. Multivariate analysis was used to evaluate the efficiency of EDR of the harbour sediments, sampled in the Arctic region (Norway and Greenland). One of the most important factors affecting the outcome was the type of sediment, emphasizing the need for developing site- and sediment specific remediation strategies. Some of the more important sediment properties were cation exchange capacity, content of carbonate, content of organic matter, grain size distribution and how the pollutants were bound in the sediment. The efficiency of EDR, with regards to metal removal, was tested in two cell designs and a stack, the 2-compartment cell being found to be most efficient with regards to faster acidification of the sediment, faster removal of heavy metals and lower energy consumption. The removal of naturally occurring metals was however also highest and if limiting the removal of these is desirable, future EDR designs may rely on both the 2- and 3-compartment cell designs. The stack was found to be the poorest design with low EDR efficiency and was not recommended in future scaling-up efforts. The experimental variables found to have the highest influence on the efficiency of EDR depended on the pollutant as well as the EDR design. In general, current density, remediation time and temperature had the greatest influence on the removal of heavy metals, while stirring rate, light and temperature were more important for removal of PAH, PCB and TBT. Optimal settings varied depending on the specific pollutant and in some cases opposite settings were optimal for the different pollutants. High temperatures (20 oC) were for instance found to improve the removal of heavy metals and TBT due to higher desorption of metals, while low temperatures (4 oC) increased the removal of PAH and PCB, probably due to microbial communities in the sediments not adapted to higher temperatures. This obviously has implications for future optimisation efforts. However, optimal settings for simultaneous removal of heavy metals, PCB and TBT to satisfactory levels were found by a multivariate model and EDR is hence a promising method for future remediation of harbour sediments.