Effects of bromide ion on the formation and toxicity alteration of halonitromethanes from nitrate containing humic acid water during UV/chlor(am)ine disinfection.

UV/chlor(am)ine are efficient for achieving multiple-barrier disinfection and maintaining residuals, while bromide (Br-) has notable impacts on the formation and toxicity of halonitromethanes (HNMs) during UV/chlor(am)ine disinfection. This study investigated the effects of Br- on HNMs formation and toxicity alteration during UV/chlor(am)ine disinfection of nitrate containing humic acid (HA) water. Results reveal that the maximum concentration of HNMs during UV/chlorine disinfection was 12.03 µg L-1 with 0.2 mg L-1 Br-, which was 22.5% higher than that without Br-, and the predominant species of HNMs were converted from trichloronitromethane (TCNM) to dibromonitromethane (DBNM) and tribromonitromethane (TBNM). However, the maximum concentration of HNMs during UV/chloramine disinfection was 3.69 µg L-1 with 0.2 mg L-1 Br-, which was increased by 26.0% than that without Br-, and the predominant species of HNMs were converted from dichloronitromethane (DCNM) to bromochloronitromethane (BCNM) and DBNM. Notably, the HNMs species and yields during UV/chloramine disinfection were less than those during UV/chlorine disinfection, primarily due to the higher concentrations of HO· and reactive chlorine/bromine species in UV/chlorine. Also, in the ranges of the Br-:Cl2 molar ratio from 0 to 0.32 and pH from 6.0 to 8.0, the Br-:Cl2 molar ratio of 0.16 and acidic pH contributed to the HNMs formation during UV/chlorine disinfection, and a high Br-:Cl2 molar ratio and neutral pH contributed to the HNMs formation during UV/chloramine disinfection. Note that the incorporation of Br- significantly improved the calculated cytotoxicity (CTI) and genotoxicity (GTI) of HNMs formed, and the calculated CTI and GTI of HNMs formed during UV/chloramine disinfection were 28.19 and 48.90% of those during UV/chlorine disinfection. Based on the diversity of nitrogen sources, the possible formation pathways of HNMs from nitrate containing HA water were proposed during UV/chlor(am)ine disinfection in the presence of Br-. Results of this study indicated that UV/chloramine can reduce the formation and toxicity of HNMs efficiently.

Effects of amines on the formation and photodegradation of DCNM under UV/chlorine disinfection.

Investigations were conducted to examine the effects of amine type and initial concentration, free chlorine concentration, UV light intensity, pH and tert-butyl alcohol (TBA) on the formation of dichloronitromethane (DCNM) under UV/chlorine. Methylamine (MA), dimethylamine (DMA) and poly-dimethyl diallyl ammonium chloride (PolyDADMAC) were selected as the amine precursors of DCNM. And the reaction products of amines were explored through observing the contents of various nitrogen under UV/chlorine. Experimental results indicated that the higher of the intensity of UV light, the concentration of amines and free chlorine, the greater of the amount of DCNM formation; the amine substance with simple structure is more likely oxidized to form DCNM, so the potential of MA to form DCNM is the largest among three amines; the formation of DCNM decreased with increasing pH from 6.0 to 8.0; due to adding TBA into the reaction solution, halogen and hydroxyl radicals were restrained which resulted the DCNM formation decreased. In the reaction process, the formation of DCNM from amines increased at the beginning, then decreased and almost disappeared due to photodegradation. During the formation and photodegradation of DCNM, the dissolved organic nitrogen could be transformed into the ammonia-nitrogen (NH3-N) and nitrate-nitrogen (NO3--N).