A review on the degradation efficiency, DBP formation, and toxicity variation in the UV/chlorine treatment of micropollutants

Many micropollutants are refractory to conventional wastewater/water treatment processes, causing attention to their potential adverse effects on aquatic environment and human health. The synchronous use of ultraviolet and chlorine (UV/chlorine) is an emerging advanced oxidation process drawing increasing interest, due to its relatively low cost and the effectiveness in degradation of refractory micropollutants via generating various reactive species, such as hydroxyl radicals ((OH)-O-center dot) and reactive chlorine species (RCS). This review documented the latest research on micropollutant degradation in the UV/chlorine process, and factors affecting the degradation efficiencies of target micropollutants, including UV fluence rate, chlorine dosage, pH, water matrix, and the reactivity of different radicals. Most recently, concerns have been raised over the formation of toxic transformation products and disinfection byproducts (DBPs) in the UV/chlorine process. The toxicity variation of micropollutants during the UV/chlorine treatment, and the multiple effects of the UV/chlorine process on the formation of DBPs were also reviewed. It was found that the toxicity variations of micropollutants in the UV/chlorine treatment were related to the compound-specific reactivity toward center dot OH and RCS. Further studies on the cost-effectiveness of the UV/chlorine process regarding micropollutant degradation without increasing the associated toxicity might be warranted.