Remediation of PFAS-contaminated soil and wastewater : Feasibility of chain treatment applying destructive techniques

Sammanfattning: 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.