Formation, toxicity, and mechanisms of halonitromethanes from poly(diallyl dimethyl ammonium chloride) during UV/monochloramine disinfection in the absence and presence of bromide ion.

Bromide ion (Br) is known as a prevalent component in water environments, which exhibits significant impacts on halonitromethanes (HNMs) formation. This study was performed to explore and compare the formation, toxicity, and mechanisms of HNMs from poly(diallyl dimethyl ammonium chloride) (PDDACl) in the absence and presence of Br in the UV/monochloramine (UV/NHCl) disinfection process. The results showed that chlorinated HNMs were found in the absence of Br, while brominated (chlorinated) HNMs and brominated HNMs were found in the presence of Br. Furthermore, the peaks of total HNMs were promoted by 2.0 and 2.4 times, respectively when 1.0 and 2.0 mg L Br were added. Also, the peaks of total HNMs were enhanced with the increase of the NHCl dosage, which were reduced with the increase of pH. It should be noted that Br induced higher toxicity of HNMs, and the cytotoxicity and genotoxicity of HNMs with the addition of 2.0 mg L Br were 78.0 and 3.7 times those without the addition of Br, respectively. Meanwhile, both the reaction mechanisms of HNMs produced from PDDACl were speculated in the absence and presence of Br. Finally, different HNMs species and yields were discovered in these two real water samples compared to those in simulated waters. These findings of this work will be conducive to understanding the significance of Br affecting HNMs formation and toxicity in the disinfection process.