Removal of per- and polyfluoroalkyl substances from drinking water using ozonation

Sammanfattning: Per- and polyfluoroalkyl substances (PFASs) are a broad group of man-made chemicals which are persistent, bioaccumulative and toxic. Due to their unique physicochemical properties PFASs are used in various industrial processes and consumer products. Their environmental persistence and ability to undergo long-range transport have made PFASs compounds of concernastheyhavebeenfoundinvariousmatricesallovertheworld. ConcerningPFASsconcentrationsinblood, breastmilkandorgansarecausedbyseveralexposureroutesi.a. contaminated drinking water. Since PFASs are not affected by conventional drinking water treatment techniques, further research on new approaches for water purification is highly needed. In this study several advanced oxidation processes (AOPs) based on ozonation were tested for their efficiency to degrade PFASs in water. Among other an established method based on heterogeneous catalysis was evaluated in pilot scale. Prior all treatment experiments, adsorption of PFASs to the catalyst surface in MilliQ, tap and water with dissolved organic carbon were evaluated. A fit according to the Freundlich adsorption isotherm model was found. Additional investigations on the adsorption velocity showed that most PFASs adsorb within 10min to the catalyst material, whereby the adsorption process is superimposed by equilibrium adjustment processes that occur slower. In the pilot scale trial drinking water was fortified with 18 different PFASs (1000ngL−1). Removal of more than 98% was found for PFASs with seven to eleven perfluorinated carbon atoms independent of the functional group. All spiked compounds were removed significantly. In a subsequent approach, all possible combinations of ozone (0.3unit), catalyst (5g) and persulfate (1:50 mole ratio spike:ammoniumpersulfate) were evaluated in MilliQ water in a 500mL laboratory scale set-up. The following trends could be observed: Results comparable to the pilot scale experiment were obtained for the combination of ozone and catalyst; ozone and persulfate as well as ozone, persulfate and catalyst. Surprisingly, the treatment with ozone only led to a removal of perfluorinated carboxylic acids (PFCAs) and perfluorooctane sulfonamide (FOSA). Thus, it has been sown, that there is potential for an improvement of already applied AOP treatment via ozone and catalyst by a combination with persulfate. Further research is needed to determine the optimal reaction conditions for this new approach.