Understanding DBP Formation during

Ying Hong, Suibing Liu, & Tanju Karanfil

rihalomethanes (THM) and haloacetic formation has not been investigated. acids (HAA) are the two major disinfec- Since there are three possible reac- Ying Hong, Ph.D., is a civil engineer in the tion byproducts (DBPs) commonly tants—NH2Cl, HOCl, and Orlando office of Black & Veatch. Suibing foundT in waters disinfected with free . (NHCl2) can interact with DOM to form Because of the potential risk of such DBPs to HAA during chloramination (Figure 1)—the Liu, Ph.D., is an environmental engineer in public health, the United States Environmental first objective of this study was to examine the the Maitland office of CDM. Tanju Protection Agency (EPA) has imposed stringent relative significance of these reactions resulting Karanfil, Ph.D., is a professor in the regulations under its /Disinfection in HAA formation during chloramination. Environmental Engineering & Earth Byproducts Rule (D/DBPR). Today, there is significant discrepancy Science Department at Clemson University. Stage 1 of the D/DBPR set the maximum among the limited chloramination literature The article was presented as a technical contaminant levels (MCLs) of THM and that has been reported by various researchers paper at the Florida Section AWWA Conference in November 2007. HAA5 at 80 and 60 µg/L, respectively, for the (Figure 2). Singer et al. (1999) reported that 50 running annual average of a water system. percent of the 72-hour dihaloacetic acid Stage 2 of the D/DBPR requires utilities to (DXAA) (the major species of HAA during comply with the DBP regulations at individ- chloramination) formed within the first hour at ual locations in distribution system (i.e., pH 8.Speitel et al.(2004) and Hua and Reckhow Materials & Methods locational running annual averages). (2005) reported even faster HAA formation To comply with current and future DBP kinetics, showing about 70-75 percent of the 72- DOM Solutions regulations, utilities have been hour DXAA formed after only 0.5 hour at pH 8. Two surface waters with significantly considering various treatment and disinfec- By contrast, in some of the preliminary different DOM characteristics were obtained tion strategies. Chloramination has received experiments of the authors’ study, only 10 from the influents of two increased attention in recent years because it percent of 72-hour DXAA formation plants in South Carolina. Myrtle Beach water almost suppresses THM formation while occurred in the first hour at pH 7, and its for- has a high specific ultraviolet absorbance at reducing HAA to 3-30 per- mation gradually increased with time. 254 nm (SUVA254) (5 L/mg-m), whereas cent of the levels observed with chlorination. All these chloramination experiments Greenville water has relatively low SUVA254 It appears that during chloramination, were performed at similar , and mono- value (2.5 L/mg-m). The DOMs in these formation and speciation of HAA, rather than chloramine were dosed to maintain approxi- waters were concentrated using a pilot-scale THM, will dictate the compliance of water mately 2 mg/L residual after 24-hour incuba- reverse osmosis (RO) system. utilities with more stringent DBP regulations. tion time as required by the uniform formation Before each experiment, RO isolate was To date, it is believed that HAA formation condition (UFC) protocol (Summers et al., diluted by distilled and deionized water during chloramination was attributed prima- 1996); therefore, research was needed to eluci- (DDW) to the target dissolved organic car- rily to the formation of chlorine (HOCl) dur- date the factors responsible for the observed bon (DOC) of 7.5 mg/L. Solution pH was adjusted by addition of 4 ing monochloramine (NH2Cl) decomposi- differences. The second objective of this study tion (reaction 1 in Figure 1); however, the sig- was to investigate the potential causes of signifi- mM carbonate buffer and acid/base solutions at different strengths. nificance of direct reaction between NH2Cl cantly different patterns observed for DXAA and dissolved organic matter (DOM) on HAA (HAA) formation kinetics in the literature. Continued on page 52

Figure 1: Conceptual illustration of HAA formation Figure 2: DXAA formation kinetics pathways during chloramination. reported by different researchers.

FLORIDA WATER RESOURCES JOURNAL • APRIL 2008 • 51 Continued from page 51 Table 1: Background effect formation (through production of HOCl on monochloramine decay and and/or formation of NHCl2) was significant- Chloramination Experiments ly suppressed. Finally, 20 mg/L ammonia was DBP formation at pH 6. Before each experiment, a fresh chlo- used for later kinetic study. ramine stock solution was prepared by mixing Parallel kinetics experiments were per- sodium (5 to 6 percent available NH3-N* TCM DCAA NH2Cl NHCl2 formed using the same DOM solution under free chlorine) and sulfate solu- (mg/L) (µg/L) (µg/L) (mg/L) (mg/L) two different ammonia conditions, i.e., in the tions in water at a Cl2/N mass ratio of 3.5:1 at absence and presence of 20 mg/L background 0 3 21 1.7 0.4 pH 9.0. Preliminary experiments were con- ammonia. The results of experiments in the ducted for each water sample to determine 10 3 18 2.1

Figure 3: Formation of HAA in the absence (NH3=0 mg/L) Figure 4: Formation of HAA in the absence (NH3=0 mg/L) and presence (NH3=20 mg/L) of additional background and presence (NH3=20 mg/L) of background ammonia ammonia at pH 6. addition at pH 9.

52 • APRIL 2008 • FLORIDA WATER RESOURCES JOURNAL A similar experiment was also per- formed at pH 9. Because monochlormaine decomposition and HOCl formation was suppressed at high pH, the difference in HAA formation was very small (within 2 ppb) for the two ammonia level experiments (Figure 4). The 24-hour DCAA concentration at pH 9 in the presence of background ammonia (where direct reaction of NH2Cl with DOM is dominant) was 28 percent of DCAA formed at pH 6, indicating that DCAA formation from direct reaction strongly depends on pH.

The Impact of Quenching Agent on HAA Kinetic Experiments It is evident from the kinetic experiment results presented in Figures 3 and 4 that no fast formation kinetics were observed in this study. Furthermore, the results obtained with the high background ammonia experiments showed that direct reaction of monochloramine with DOM plays the major role in the HAA formation. Figure 5: HAA formation kinetics determined at pH 6 and 9 using Currently, EPA Method 552.3, approved Na2SO3 or NH4Cl as quenching agents. for compliance monitoring under the D/DBPR, requires the use of (NH4Cl) as a chlorine quenching Chloramination experiments also were per- agent for HAA samples. NH4Cl is not a formed to check the reliability of stoichiomet- Acknowledgements quenching agent for NH2Cl; however, NH4Cl ric amount of Na2SO3 on preserving HAA significantly minimizes NH2Cl decomposi- samples. Results (data not shown) indicated This work was supported by a research tion, as discussed above, without eliminating that no HAA concentrations in the samples grant from the American Water Works it from sample vials. were changed after three days’ storage time, Association Research Foundation (project Since the direct reaction of NH2Cl with since residuals of NH2Cl in the sample were 2993). The authors also acknowledge the DOM appears to be dominant in HAA for- destroyed by Na2SO3; however, HAA concen- assistance of Hocheol Song and Olivia Orr mation, the residual NH2Cl can continue to trations in samples quenched with NH4Cl of Clemson University and personnel of react with the DOM until the sample is increased with sample storage time because of Myrtle Beach and Greenville water treat- extracted. As a result, the use of NH4Cl may the continued reaction of NH2Cl and DOM. ment plants who participated in this study create an artifact on the HAA determination for sample collection. Detailed discussions in chloraminated samples. Conclusions of this study can be found at Journal of To assess the significance of quenching AWWA, August 2007. agent selection on chloramination kinetics, a  Experiments performed in the presence comparison experiment was performed at (where HOCl and NHCl2 formation is signif- References pH 6 and pH 9 using Myrtle Beach DOM. icantly suppressed) and absence (where Chloraminated samples were quenched NH2Cl decomposition can occur) of back- • Hua, G. and Reckhow, D.A. (2005). Factors using either a stoichiometric amount of ground ammonia indicated that a major Affecting the Formation of Disinfection By- Na2SO3 or 100 mg/L of NH4Cl at the end of amount (~80 percent) of HAA is formed product during Chlorination and each contact time. They were stored immedi- from the direct reaction of NH2Cl with DOM. Chloramination. Proceeding of AWWA ately in a refrigerator (4-6ºC) until extrac- DXAA is the major HAA species formed dur- Water Quality Technology Conference, tion, which was performed for all samples ing chloramination, and its formation Quebec, Canada. together right after the last sample of the decreased significantly with increasing pH. • Singer, P.C.; Harrington, G.W.; Cowman, kinetic experiment (48-hour). The results are  Selection of a quenching agent is impor- G.A.; Smith, M.E.; Schechter, D.S; presented in Figure 5. tant to obtain reliable results from chlo- Harrington, L.J. (1999). Impacts of The samples quenched with NH4Cl ramination experiments. The use of Ozonation on the Formation of showed a significantly higher and faster HAA NH4Cl, the quenching agent recommended Chlorination and Chloramination By- formation than the samples quenched with by EPA Method 552.3 for DBP samples, Products. American Water Works Na2SO3 at both pH values. The difference can create an artifact on the HAA results. Association Research Foundation Report. between the two kinetic patterns (i.e., NH4Cl Since NH4Cl does not quench the residual • Speitel G.E.; Pope, P.G. ; Collins, M.R. and vs. Na2SO3) increased with decreasing reac- chloramines, the reactions of chloramines Martin-Doole, M. (2004). Disinfection By- tion times. These observations indicated that with DOM forming HAA can occur until Product Formation and Control During the fast kinetic patterns reported in Figure 2 the samples are analyzed. As a result, false Chloramination. American Water Works were caused by unsuccessful quenching and high HAA concentrations are measured at Association Research Foundation Report. long sample storage time. early reaction periods. The type of quench- • Summers, R.S.; Hooper, S.M.; Shukairy, These findings clearly show that selection ing agent used appears to be the cause of H.M.; Solarik, G.; and Own, D. (1996). of a quenching method has an impact on the different kinetic patterns reported for chlo- Assessing DBP yield: Uniform Formation determination of HAA formation. ramination kinetics in the literature. Conditions. Jour. AWWA, 88:6:80. 

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