Performance of in-service granular activated carbon for perfluoroalkyl substances removal under changing water quality conditions

Abstract

Granular activated carbon (GAC) adsorption is one of the best available technologies for removing perfluoroalkyl substances (PFASs) from drinking water. However, GAC processes in full-scale drinking water treatment plants frequently encounter unstable, even negative removal efficiency on PFASs due to the lack of understanding between the GAC characteristics and the PFASs polluted water quality conditions. In this study, the scenarios of raw water pre-chlorination and emergency contamination by multiple PFASs were simulated to evaluate the PFASs control performance by in-service GAC with different properties and ages. The results showed that the adsorption of a relatively longer-chain PFAS by the in-service GAC can be achieved by replacing the pre-adsorbed natural organic matter (NOM). The increased lower molecular weight NOM after pre-chlorination could compete with PFASs for adsorption sites and exacerbate the pore blockage, thus significantly weakening the PFASs removal ability of in-service GAC. When multiple PFASs entered the water by emergency contamination, the PFASs with stronger hydrophobicity could replace the PFASs with less hydrophobicity that had previously been adsorbed on GAC. GAC with a higher proportion of micropores had a lower risk of PFASs leakage facing the water quality changes.

Keywords: Adsorption; Granular activated carbon; Natural organic matter; Perfluoroalkyl substance; Water quality changes.