Proportion of bromo-DBPs in total DBPs during reclaimed-water chlorination and its related influencing factors

Abstract

During the chlorine disinfection of reclaimed-water, the proportion of bromo-disinfection by-products (bromo-DBPs) in total DBPs is affected by chlorine dosage, reaction time, pH, ammonia nitrogen (NH 3 -N) and preozonation. Results show that bromo-trihalomethanes (bromo-THMs) form more easily than bromo-haloacetic acids (bromo-HAAs) and bromine incorporation in DBPs decreases with the increase of chlorine dosage. Within 5 h, bromine incorporation in THMs (n(Br)) increases but bromine incorporation in HAAs (n′(Br)) decreases with the extension of reaction time; however, n(Br) decreases and n′(Br) keeps relatively constant at a longer reaction time. Furthermore, bromine incorporation in DBPs is low under acidic and alkaline conditions. The increase of NH 3 -N concentration inhibits the formation of chloro-DBPs, resulting in the increase of n(Br) and n′(Br) to some extent. Preozonation enhances the formation of HOBr and the increase of bromine incorporation in DBPs; however, ozone of a high concentration oxidizes HOBr to its salt form, leading to the decrease of bromine incorporation in DBPs.bromine, chlorine disinfection, bromo-DBP Most sewage treatment plants (STPs) receive complex mixtures of urban and industrialized discharges. Even after secondary treatment, they still contain a large amount of dissolved organic matter (DOM), which serves as a precursor in the chlorination process to the formation of potentially harmful disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) [1,2] . There is also bromide ion (Br − ) in the effluent which cannot be easily removed via bio-treatment. During chlorine disinfection, Br − can be oxidized to hypobromous acid (HOBr) or hypobromite by hypochlorous acid (HClO) [3] . In both halogen substitution for THMs and dihalogenated HAA formation, HOBr shows an activity 20 times stronger than that of HOCl [4][5][6] . Furthermore, bromo-DBPs are reported to be more carcinogenic than chloro-DBPs [7][8][9][10] . Thus, more and more researches have focused on the control of bromo-DBPs.It is reported that as the Cl 2 /Br − molar ratio increases, the concentrations of chloroform (CHCl 3 ), bromodichloromethane (CHCl 2 Br) and dibromochloromethane (CHClBr 2 ) increase except for that of bromoform (CHBr 3 ) [5] . Increasing bromide concentration gradually shifts THMs and HAAs speciation from chlorinated species to the mixed bromochloro species during chlorination [6] . Furthermore, the Br − /DOC molar ratio was reported to influence the distribution of DBPs species. As the Br − /DOC molar ratio increases, dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) decrease rapidly, whereas dibromoacetic acid (DBAA) and

Methods of Controlling THMs and HAAs Formation during Reclaimed Water Chlorination

“…When compared with some other research, the DBP yield ratio (µmol DBPs/mmol DOC) was relatively higher (especially for the HAAs in water) [8,11,12], this might be caused by the great SUVA value in the water of this study [12,13]. In order to lower effluent DBP concentration (which brought waterquality risk) of the RWTP in this study, increasing ammonia concentration, adjusting pH value and ozonation of the samples before chlorination were tested and compared in the following sections.…”

“…1, n(Br) and n'(Br) both began with increase and changed to decline then. This is because bromo-THMs and bromo-HAAs form through the process that Bris oxidated into hypobromous acid firstly and the DBP precursors react with HOBr to be bromo-DBPs then [11]. As the bromide ion might be limited in the water, the bromo-DBPs formation potential was restricted.…”