Removal efficiency of perfluoroalkyl substances (PFASs) in drinking water : evaluation of granular activated carbon (GAC) and anion exchange (AE) using column tests, and the effect of dissolved organic carbon

Sammanfattning: Poly- and perfluoroalkyl substances (PFASs) are a group of environmental contaminants that have gained increasing attention due to their potential to bioaccumulate, environmental persistence and potential toxicity. PFASs have been found in surface water, sediment, air, soil, sludge and ice caps globally, as well as in wildlife and humans. Furthermore, PFASs have also been detected in drinking water, leading to raised concerns for human health, since drinking water is one of the most significant sources of PFASs for the general population. Conventional water treatment techniques have shown to be ineffective removing PFASs, highlighting the importance for further research to develop efficient removal techniques. The aim of this study was to investigate the removal efficiency of PFASs in water using two treatment techniques; granular activated carbon (GAC), type Filtrasorb 400®, and anion exchange (AE), type Purolite A-600. Additionally, the effect of dissolved organic carbon (DOC) on removal efficiency was studied. The removal efficiency of PFASs was studied in pilot-scale column experiments at Bäcklösa drinking water treatment plant (DWTP) in Uppsala, Sweden. The laboratory batch experiments were performed at Swedish University of Agricultural Sciences (SLU), Uppsala. The results from the column experiment indicated a decrease in removal efficiency with increasing number of bed volumes (BVs) for both GAC and AE. The average removal efficiency of all PFASs (n=14) during the 140 day column study was 65% for both GAC and AE. At the end of the column experiment, the average removal efficiency of all PFASs was 49% for GAC and 53% for AE. Removal efficiency was influenced by functional group; perfluoroalkane (-alkyl) sulfonic acids (PFSAs) were more efficiently removed than perfluoroalkyl carboxylic acids (PFCAs) (on average 56% vs 38% for GAC, respectively, and 82% vs 28% for AE, respectively). In addition, the perfluorocarbon chain length influenced the removal efficiency. Results from the column experiment indicated higher removal efficiency as the perfluorocarbon chain length increased. In contrast, the results from the batch experiments indicated the opposite; decreasing adsorption to GAC and AE as the chain length increased. Furthermore, presence of DOC in the water affected the removal efficiency of the investigated PFASs. However, the results indicated, contrary to the few studies previously performed on DOC and removal efficiency of PFASs, enhanced sorption of PFASs to GAC with increasing DOC concentration, and decreased PFAS sorption to AE as the DOC concentration increased. In addition, the removal efficiency of GAC and AE varied using water types with different DOC origin, indicating that DOC characteristics influence the removal efficiency of PFASs in water.