Formation Of DBPs Research Articles

Modeling an ozone bubble column for predicting its disinfection efficiency and control of DBP formation

The prediction models describing the disinfection efficiency, the formation of aldehydes and the control of DBPs in the ozone bubble column were developed through a systematic approach. At low applied ozone doses, the predicted Ct values increased slightly with increasing gas flow rate. As the applied ozone dose increased, the influence of the gas flow rate on the Ct parameters became more apparent. The aldehyde formation increased to a maximum value when the ozone doses increased from 0.2 to 1.1 mg O 3/mg TOC; whereas a further increase of the ozone dose to 1.8 mg O 3/mg TOC decreased the aldehyde concentrations. The concentration profiles of aldehyde and DBP in the ozone bubble column were modeled at the different ozone dosages and compared with the experimental data. The utilization of a two-step reaction mechanism predicted the aldehyde formation reasonably well. Furthermore, the relationship between the optimization of ozone dosages and the disinfection efficiency, aldehyde formation and control of DBPs was discussed.

Formation of Cyanogen Bromide and Other Volatile DBPs in the Disinfection of Bromide-Rich Lake Water

Production of cyanogen bromide (CNBr) and other volatile DBPs was studied in bromide-rich lake water during disinfection with chlorine, chloramine, and chlorine dioxide. The different disinfectants were dosed to the lake water in laboratory experiments, and the resulting concentrations of CNBr, trihalomethanes (THMs), and haloacetonitriles (HACNs) were measured. CNBr concentration is a resultant of formation and decomposition by hydrolysis. Maximum concentration (36 μg/L) was obtained at low chlorine dose (1.5 mg/L) at pH 7.5 and 10 h contact time. Under these conditions, the molar distribution of the volatile DBPs was 50% CNBr, 40% THMs, and 10% HACNs. It is suggested that CNBr is formed by the reaction of hypobromous acid with organic N precursors present in lake water. Fulvic acid was found to be a good precursor for THMs but a poor precursor for CNBr. With chloramination, yields of CNBr, THMs, and HACNs were much lower, only 6, 11, and 2 μg/L, respectively. CNBr concentration was stable for 10 days. Chlorine dioxide produced insignificant quantities of CNBr, THMs, and HACNs, less than 1 μg/L. A combination of chlorine dioxide and chloramine enhanced production of CNBr and THMs to maximum yields of 7.8 and 19 μg/L, respectively.

Philadelphia drinking water

The formation of regulated and emerging halogenated carbonaceous (C-) and nitrogenous disinfection by-products (N-DBPs) from the chlor(am)ination and UV irradiation of tyrosine (Tyr) was investigated. Increased chlorine contact time and/or Cl2/Tyr ratio increased the formation of most C-DBPs, with the exception of 4-chlorophenol, dichloroacetonitrile, and dichloroacetamideChloroform and dichloroacetic acid increased with increasing pH, dichloroacetonitrile first increased and then decreased, and other DBPs had maximum yields at pH 7 or 8. The addition of ammonia significantly reduced the formation of most C-DBPs but increased 4-chlorophenol, dichloroacetonitrile, dichloroacetamide, and trichloroacetonitrile yields for short prechlorination contact times before dosing ammonia. When UV irradiation and chlorination were performed simultaneously, the concentrations of the relatively stable C-DBPs increased, and the concentrations of dichloroacetonitrile, dichloroacetamide, and 4-chlorophenol decreased with increasing UV dose. This information was used to develop a mechanistic model for the formation of intermediate DBPs and end products from the interaction of disinfectants with tyrosine.