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- Niarchos, Georgios
(författare)
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Remediation of per- and polyfluoroalkyl substance-contaminated soil and groundwater, using electrokinetic and stabilisation methods
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Per- and polyfluoroalkyl substances, commonly known as PFAS, are emerging contaminants with a worldwide environmental distribution and a concerning (eco)toxicological profile. The omnipresence of PFAS in various environmental media poses risks to the quality of our drinking water sources. Soils can act as inventories of PFAS plumes, which can slowly find their way into water resources. There is an imperative need for treatment applications at the pollution hotspots to prevent the spreading of PFAS into water bodies. This thesis aimed to investigate the potential of two technologies for treating PFAS-contaminated soils and groundwater: one focused on PFAS removal using electrokinetics and the other on their immobilisation in the subsurface using stabilisation with colloidal activated carbon (CAC). The findings of this thesis show that both methods can be promising; however, their effectiveness depends on compound-specific parameters and field considerations at the contaminated sites. The electrokinetic removal was highly effective for short-chain PFAS, with up to 99% removal for PFAS with C≤6 in their perfluorocarbon chain. Electrokinetic removal was also coupled with immobilisation by transporting and entrapping 75% of ∑PFAS to GAC. Conversely, stabilisation with CAC was more successful for long-chain PFAS and more for perfluoroalkyl sulfonates (PFSAs) than perfluoroalkyl carboxylic acids (PFCAs), with lab tests indicating an average of eight times retardation of PFAS in CAC-treated soils. Desorption from CAC was not significant, signifying that immobilisation with CAC can be effective in the long term. Challenges in applying both methods were also identified; electrokinetic remediation can be limited due to the low solubility of certain PFAS and the depletion of ions from the soil matrix, which might increase the complexity of the treatment and its costs. Stabilisation with CAC did not prove viable for the treatment of short-chain PFAS. Moreover, CAC was partially flushed out of the soil, with column tests showing a loss of 22% of the added CAC. These aspects must be considered in full-scale treatment applications to ensure optimal treatment. The PFAS composition is another critical parameter in stabilisation treatment, as the results showed competition among PFAS for sorption sites, with FOSA dominating its counterparts and short-chain PFAS being outcompeted by their long-chain homologues at higher concentrations. Immobilisation was also tested in a field study, which confirmed the results of the lab experiments, exhibiting the potential for PFAS contamination and highlighting the challenges. Nonetheless, the effectiveness of the stabilisation methods needs to be contextualised within the requirements and limitations of each contaminated site. In the future, optimising the technologies studied in this thesis can likely lead to higher efficiency, while combining these methods with other technologies, such as degradation, can be beneficial for the holistic management of PFAS-impacted sites.
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| 2. |
- Uwayezu, Jean Noel
(författare)
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Remediation of PFAS-contaminated soil and wastewater : Feasibility of chain treatment applying destructive techniques
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals ubiquitously distributed in soil and aquatic media, resulting from their wide range of industrial applications. Today, PFAS is a global concern due to their persistence in the environment and their adverse effects on humans and the ecosystem. Despite the considerable efforts to develop PFAS treatment methods, a viable solution has not yet been established.This Ph.D. thesis investigated the potential of applying electrochemical oxidation (EO) and UV radiation assisted with persulfate (PS/UV), both individually and in combination(EO-UV), for PFAS degradation in solutions. Furthermore, integrating destructive technique showing the most promising results, i.e., EO, within a treatment chain comprising soil washing (SW) and foam fractionation (FF) was assessed to eliminate PFAS from contaminated soil. Perfluorooctanesulfonic acid (PFOS) accounted for 97% of the PFAS contamination in the soil. The EO and PS/UV showed the potential to break down PFAS in spiked solutions. Removal of 99 % perfluorooctanoic acid (PFOA) was found at a current density of 23.4 mA cm-2 and 4 h whereas 80% PFOA, 60% PFOS, and 57% perfluorobutanoic acid (PFBA) were removed in 4 h and in the presence of 5 g L-1 Na2S2O8. By transferring the best experimental conditions for the treatment of PFAS-contaminated wastewater, the removal of 56% ∑11PFAS was reached using EO whereas PS/UV led to an increase in the concentration of PFAS. It was highlighted that optimizing EO would lead to higher removal and reduce energy consumption. Nevertheless, PFAS removal from groundwater using PS/UV treatment was almost as effective as in synthetic solutions, highlighting its potential for treating PFAS in matrix-free water. Combining EO and UV led to substantial removal improvements due to degradation processes in both systems, probably due to synergistic effects. Adding FF to soil SW led to an average removal of 82% and 92% ∑11PFAS in soil and leachate respectively, at the L/S of 5 (five washing cycles) and pH 11.5. As per estimations, employing 20 treatment cycles could result in 94% and 91% of PFAS removal in soil and leachate. The EO at 60 mA cm-2 and 2 h removed 88.3% of ∑11PFAS, which was contained in wastewater resulting from the FF process. Overall, the SW-FF-EO three-stage treatment led to the removal of 67% ∑11PFAS, estimated to be 88% if the SW-FF consecutive treatments are repeated 20 times. Incorporating FF in the treatment chain enabled leachate recycling and reduced water volume needs in the soil treatment process, but also concentrated PFAS in a smaller water volume, thereby allowing the EO step to be more cost-effective.
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