Research progress on UV/chlorine advanced oxidation process for treating emerging contaminants

The ultraviolet/chlorine (UV/Cl) advanced oxidation process is an emerging water treatment technology that combines ultraviolet irradiation with free chlorine to generate reactive radicals such as ·OH, ·Cl and \mathrmCl_2^\cdot - . This process demonstrates high efficiency in degrading various emerging micropollutants, including antibiotics, pharmaceutical residues, and endocrine-disrupting compounds, while simultaneously offering disinfection capabilities. It outperforms conventional UV/H₂O₂ advanced oxidation for degrading certain contaminants, can maintain residual chlorine in distribution systems, and is readily implementable through upgrades to existing facilities. This review summarizes the radical generation mechanism, oxidation properties, reaction mechanism, and actual degradation efficacy of various emerging contaminants in the UV/Cl process. It discusses the significant influence of key factors such as pH, chlorine dosage, and water components (e.g., dissolved organic matter, carbonates/bicarbonates, halide ions). Furthermore, the formation patterns and potential control strategies of disinfection byproducts (DBPs) are examined. Currently, the process still faces challenges in scaling up to large-scale application, such as the lack of long-term operational data, the need to clarify its efficacy in removing specific pollutants (e.g., persistent organic pollutants (POPs), microplastics) and the resulting changes in overall toxicity, and a substantially increased risk of forming DBPs, chlorates, and bromates when the source water contains high levels of organic matter, ammonia, or bromide ions. Additionally, the formation mechanisms involve radical attacks and the activation of inert substances. Future research needs to focus on in-depth studies of pollutant degradation and byproduct control mechanisms, optimization of process parameters, exploration of combined process flows, and thorough techno-economic analyses. These steps are essential to overcome the current limitations and advance the practical application of this technology for safeguarding water environmental security.