Per- and polyfluoroalkyl substances (PFAS) are a rising topic in the field of contaminated sites around the world, with destruction of these being an area in dire need of innovation. Previous experiments of destructive character have been proven efficient using boron doped diamond electrodes (BDD) in small scale electrochemical cells. Further need for experimentation on actual site conditions is needed to further evaluate the use of this method, as well as research on alternative electrode materials to reduce the cost of remediation. In this study, four cells containing contaminated soil were used: one with BDD electrodes, one with iron electrodes and two control cells. The iron electrodes were used to investigate if a less costly electrode material could achieve any degree of PFAS degradation. For the experiment a soil from a previous firefighting training site where firefighting foam containing high amounts of PFAS (620 g/kg soil concentration) was used. During the first phase of the experiment a constant flow of deionized water was added to the cells containing the soil, and porewater was sampled at the in- and outflow along with the soil porewater, on a weekly basis, to evaluate the distribution of PFAS to provide information about possible degradation taking place. The extent of degradation was not quantified. However, due to differences in the molecular composition of the analysed PFAS a trend where short-chain PFAS increase throughout the experiment in the BDD cell indicated that short-chain PFAS were generated, which is an expected by-product in electrochemical oxidation of PFAS. No short-chain PFAS generation was seen in the iron electrode cell, nor was there a high amount present in the control cell leachate. Further, leaching of PFAS was more efficient in the control cells, while PFAS in the BDD and iron electrode cell were retained or leaching was slowed down, most likely due to the electrode interaction with PFAS in porewater.Additionally a second phase where water flow through was halted and the cells were run in a batch mode was conducted to see PFAS degradation in stagnant conditions over time. In the stagnant cell in the second phase, only low PFAS concentrations in porewater were recorded while no degradation was established. Further, fluoride analysis recorded F- concentrations in the range of M, where the limit of detection was M, which limited the confirmation of PFAS mineralisation in soil. From this study insight of the difficulties with soil treatment of PFAS using electrokinetic method was highlighted, with sampling being a key factor in the accuracy of the result. For a more accurate establishment of the degradation experiments in a closed cell, with more extensive sampling throughout the entire column would be necessary. This is needed to generate a clearer picture of changes in PFAS concentration in the soil from the presumed degradation, coupled with a mass balance to provide the fate of PFAS in this type of setup.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-92431 |
| Date | January 2022 |
| Creators | Öhberg, Alexander |
| Publisher | Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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