Caffeine degradation via UV/trichloroisocyanuricacid: Kinetic, influencing parameters and chlorinated disinfection byproducts

Abstract

The combination of ultraviolet (UV) and chlorine-based disinfectants has garnered significant attention in recent years. Trichloroisocyanuricacid (TCCA), an attractive alternative to chlorine, has been widely used in swimming pools. The combination of UV and TCCA (UV/TCCA) may be an emerging treatment for removing micropollutants in swimming pools. However, the performance of UV/TCCA on degrading micropollutants has not been investigated. In this study, the kinetic, influencing parameters, and disinfection byproducts during the degradation of caffeine (CAF) in UV/TCCA system were investigated. CAF was significantly removed by UV/TCCA process (over 94.6 % within 15 min), which was mainly attributed to the contribution of reactive chlorine species (77.1 %) and •OH (22.9 %). As pH was increased from 6.0 to 9.0, the reaction rate constant of CAF demonstrated an initial upward trend followed by a subsequent decline, reaching its peak value at pH 7.2. Higher TCCA dosage significantly promoted the degradation of CAF, while the high concentrations of body fluid analogue and inorganic anions (i.e., HCO3−, SO42−, Br−, Cl−) inhibited the degradation of CAF. Furthermore, UV/TCCA effectively controlled the formation of typical disinfection byproducts and maintained higher free chlorine concentration compared to UV/NaClO under similar reaction conditions. This study filled the knowledge gaps on UV/TCCA process, providing comprehensive evidence for the potential application of UV/TCCA.