Comparison of diatrizoate degradation by UV/chlorine and UV/chloramine processes: Kinetic mechanisms and iodinated disinfection byproducts formation

This study compared the degradation efficiency of diatrizoate (DTA) by UV/chlorine and UV/chloramine processes. DTA could be effectively degraded by the UV/chlorine and UV/chloramine processes compared with chlorination and chloramination solely. Although the UV/chlorine process was more sensitive to the variations of oxidant dosages, solution pH, the concentration of bicarbonate and chloride, UV/chlorine degraded DTA more efficiently than UV/chloramine process. The reactive chlorine species (RCS) and hydroxyl radical (HO center dot) are predominant contributors to DTA degradation in the UV/chlorine and UV/chloramine processes respectively, and the specific contribution of each reactive specie changed with solution pH. The performance of UV/chlorine and UV/chloramine processes on DTA degradation was obviously inhibited in natural waters (e.g., wastewater, rainwater, river water and tap water), however, degradation of DTA in the UV/chlorine are still satisfactory compared with UV/chloramine process. Formation of chloroform, dichloroacetonitrile, and iodoform (IF) from DTA was observed in both UV/chlorine and UV/chloramine processes. It is notable that formation potential of IF from DTA was significantly enhanced in UV/chloramine process, and thus the overall cytotoxicity of generated DBPs in UV/chloramine process is far greater than that in UV/chlorine process.