Optimization of chlorine-based disinfection for the control of disinfection by-products formation and CODMn: A case study

Control of chemical oxygen demand (CODMn) and disinfection by-products (DBPs) formation is a major challenge for drinking water treatment plants (DWTPs), especially for those that use source water with high levels of natural organic matter (NOM) and bromide ions (Br−). This study focused on the Luwen DWTP with conventional treatment processes, and used bench- and plant-scale tests to optimize chlorine-based disinfection for the control of total trihalomethane (TTHMs) and CODMn. In cases of pre-chlorination at 1.3 mg/L, the post-chlorination at 1, 2, 3, and 4 mg/L of chlorine contributed to high TTHMs values of 0.94, 1.65, 2.07, and 2.21, respectively. At the same doses of total chlorine, the two-point chlorination formed less THMs than the one-point dosing strategy, although it was achieved at the expense of lowered CODMn removal efficiency. The combined use of chlorine and monochloramine greatly decreased THMs formation, and a more significant decrease of TTHMs was observed at shortened time intervals between dosing chlorine and ammonia. The post addition of ammonia in the Cl2–NH2Cl process also impacted the incorporation of Br− into THMs and increased the ratios of brominated THMs (Br-THMs) to THMs by ceasing chlorine activity. The field study compared the levels of TTHMs, CODMn, ammonia, and residual chlorine in the treatment chain and the distribution systems among three disinfection scenarios of Cl2, NH2Cl, and Cl2 + Cl2 + NH2Cl. The Cl2 + Cl2 + NH2Cl process was better than the other two processes for the simultaneous control of THMs formation and CODMn.

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► Optimization of chlorine-based disinfection scenarios for TTHMs and CODMn control.
► Two-point chlorination forms less THMs than the one-point dosing strategy.
► Lower TTHMs is observed at shortened time intervals between dosing Cl2 and NH3.
► Post NH3 addition increases the ratios of Br-THMs to THMs in Cl2–NH2Cl process.