Kinetics and speciation of brominated disinfection by-products during ozonation

To evaluate control strategies of ozonation disinfection by-products (DBPs), batch ozonation experiments were conducted using six source waters. Trade-offs were found between the formation potentials of bromate, organic bromines, and aldehydes at a fixed ozone dose. However, if the DBP formation potentials were normalized with ozone exposure (OE), it was demonstrated that acid addition is effective to minimize organic bromines and bromate, while maintaining a reasonable OE value and not significantly increasing aldehyde formation.; Then, to further investigate the kinetics of organic bromine formation, the combination of a sequential stopped-flow analysis and a specific and sensitive probe for HOBr, an ABTS method, was introduced. This new method determined the reaction rates of HOBr with phenolic compounds, one of the major chemical components in natural organic matters (NOM). The apparent second-order rate constants increased with pH between 4.0 and 8.5 suggesting that a major reaction pathway is the reaction between phenoxides and HOBr. Bromination of phenols by HOBr was found to be approximately 1000 times faster than chlorination by HOCl. Thus bromination of NOM can be a major sink of bromine species even under a low bromide condition. The new method was also applied to evaluate the kinetics of the reaction between NOM and HOBr. Multiple reaction phases were found during the reaction. The number of reaction sites for the fast reaction phase ranged from 0.2 to 0.9 μmole per unit mg C, and was correlated to both Specific UV absorbance (SUVA) and specific phenolic content. The apparent second-order rate constants for the reaction between HOBr and NOM ranged from 3 × 105 to 1.0 × 106 M−1 •s−1. Although preozonation tended to reduce it, the fast reaction component for HOBr remained even after ozonation. A chemical quenching method using 2-chlorophenol revealed that bromination is a dominant reaction pathway during the reaction between NOM and HOBr.