Influences of Bromide Ions upon Chlorination Characteristics of Chlortoluron as Precursor of NDMA

Abstract:

The chlorination kinetics of N nitrosodimethylamine(NDMA) precursor, Chlortoluron, controlling different concentrations of bromine ions under different pH,was investigated in this study. Results show that degradation of Chlortoluron still meets pseudo first order dynamic model when different dosages of bromine ions are controlled at scheduled pH of 6, 7, 10 (concentrations of Chlortoluron and Cl2 are 9.4 μmol·L-1 and 188.0 μmol·L-1, respectively). The degradation rate of Chlortoluron increases with concentrations of bromide ions at pH 6 and 7. Chlortoluron degrades faster under more acidic conditions. This phenomena are probably related to the generation of HOBr in the system. Nevertheless, when pH is 10, variation of bromide ions has no significant impact on the degradation rate, which may be attributed to non reaction of ClO- and Br- and no generation of HOBr. Based on the kinetics analysis, this study obtains the linear relationship between kobs and ［Br2］/［Cl2］ at these pH conditions. Then by solving ordinary differential equations, the reaction rate constant of HOBr and Chlortoluron is calculated(k5=(1.95±0.44)×105). Simultaneously, from viewpoint of dynamics, this relatively far high rate constant also explains the distinct faster degradation rate of Chlortoluron with the presence of bromine ions.