Nine per- and polyfluoroalkyl substances (PFASs), including six perfluoroalkyl carboxylic acids (PFCAs) and three perfluoroalkyl sulfonic acids (PFSAs), were tested to find their adsorption selectivity from surface water and the feasibility of the powder activated carbon (PAC) process between the perchlorination and coagulation processes by operating parameters such as mixing intensity, dosage, contact time, initial pH, and concentration of perchlorination. The removal efficiency of four types of PAC revealed that the coal-based activated carbon was clearly advanced for all of the PFASs, and the thermal regenerated PAC did not exhibit a significant reduction in adsorption capacity. The longer carbon chain or the higher molecular weight (MW) obtained a higher adsorption capacity and the MW exhibited a more proportional relationship with the removal efficiency than the carbon chain number, regardless of the PFCA and PFSA species. Approximately 80% and 90% equilibria were accomplished within 60 and 120 min for the long chain carbon PFAS, respectively, while for the short chain PFAS, 240 min was required to reach 85% equilibrium. The effect of mixing intensity (rpm) was not considered for the removal of the PFAS, although it was relatively influenced in the short PFAS species. Due to the surface charge of the PAC and the properties of protonation of the PFASs, the acid condition increased the PFASs’ adsorption capacity. The prechlorination decreased the removal efficiency, and the reduction rate was more significantly influenced for the short chain PFAS than for the long chain PFAS.

Transformation of atenolol (ATN), a micropollutant containing a secondary (2°) amine moiety, can be significantly enhanced in water treatment with sequential and combined use of chlorine and UV (chlorine/UV) through photolysis of the N–Cl bond. This study investigated the transformation kinetics, products, and mechanisms of the amine moiety of ATN in chlorine/UV (254 nm). The fluence-based, photolysis rate constant for N–Cl ATN was 2.0 × 10–3 cm2/mJ. Transformation products (TPs) with primary (1°) amines were mainly produced, but TPs with 2° and 3° amines were also formed, on the basis of liquid chromatography (LC)/quadrupole-time-of-flight/mass spectrometry and LC/UV analyses. The amine-containing TPs could be further transformed in chlorine/UV (with residual chlorine in post UV) via formation and photolysis of new N–Cl bonds. Photolysis of N–Cl 1° amine TPs produced ammonia as a major product. These data could be explained by a reaction mechanism in which the N–Cl bond was cleaved by UV, forming aminyl radicals that were transformed via 1,2-hydrogen shift, β-scission, intramolecular addition, and 1,2-alkyl shift. Among these, the 1,2-alkyl shift is newly discovered in this study. Despite enhanced transformation, only partial mineralization of the ATN’s amine moiety was expected, even under chlorine/UV advanced oxidation process conditions. Overall, the kinetic and mechanistic information from this study can be useful for predicting the transformation of amine moieties by chlorine/UV water treatment.

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