Removal of micropollutants in drinking water using UV-LED/chlorine advanced oxidation process followed by activated carbon adsorption

Abstract

This study investigated the removal of three selected micropollutants (i.e., bisphenol A, diclofenac and caffeine) in drinking water using the UV-LED/chlorine advanced oxidation process (AOP) followed by activated carbon adsorption. The degradation of bisphenol A, diclofenac and caffeine was predominantly contributed by chlorination (>60%), direct UV photolysis (>80%) and radical oxidation (>90%), respectively, during the treatment by the UV-LED/chlorine AOP at three tested UV wavelengths (i.e., 265, 285 and 300 nm). The most effective UV wavelengths for the degradation of bisphenol A, diclofenac and caffeine were 265, 285 and 300 nm, respectively. The degradation of all the three micropollutants was enhanced with increasing pH from 6 to 8, though the reasons for the pH dependence were different. The residues of the micropollutants and their degradation (by)products were removed by post-adsorption using granular activated carbon (GAC). Interestingly and more importantly, the adsorption rates of the degradation (by)products were 2–3 times higher than the adsorption rates of the corresponding micropollutants, indicating the formation of more adsorbable (by)products after the AOP pre-treatment. The UV-LED/chlorine AOP followed by GAC adsorption provides a multi-barrier treatment system for enhancing micropollutant removal in potable water. The findings also suggest the merit of the sequential use of UV-LEDs followed by GAC in treating chlorine-containing potable water in small-scale water treatment systems (e.g., point-of-use or point-of-entry water purifiers).