Science of Chloramination. Maine Water Utilities Association Michael Koza, Portland Water District June 2010

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1 Science of Chloramination Michael Koza, Portland Water District June 2010

2 Chloramination The process of combining chlorine and ammonia to create a combined form of chlorine for drinking water disinfection

3 Combined Compounds Chloramine is a general term that describes three related compounds: MONOchloramine, NH2Cl DIchloramine, NHCl2 TRIchloramine, NCl3 Monochloramine is preferred for drinking water disinfection.

4 Chloramine structure The molecular structure of all three chloramine compounds resembles ammonia, NH 3 A chlorine atom will replace one, two, and three hydrogen atoms respectively for the formation of mono-, di-, and trichloramines. Monochloramine Trichloramine Dichloramine

5 Why Chloraminate? Provide Longer Lasting Residual Driving factor for PWD in 1939 Reduce DBP Formation To meet lower MCL s of Stage 1 D/DBP Rule Reduce T & O if applicable

6 Chloramine History Successful usage in s (16%) Decreased in popularity in s - scarcity of ammonia - World War II (2.6%) SDWA in 1974 and THM regs (23%) More stringent D/DBP Rules pushing % up ~30%

7 Utility Considerations For a drinking water utility, chloramination may or may not be a good alternative to free chlorination. What is the source water type and quality and the overall treatment process required to produce potable drinking water. Even with the full range of chloramine benefits, consideration must be given to secondary impacts associated with chloramination primarily the potential for nitrification within the distribution system.

8 Considerations (cont.) With chloramination, an additional chemical must be purchased, stored, and applied to the process. To form the preferred chloramine compound, the appropriate weight ratio of chlorine and ammonia must be determined and then carefully managed. Free ammonia entering the distribution system must be monitored and limited to reduce the potential for nitrification. Beyond that, it may be necessary to incorporate any number of steps to actively control nitrification.

9 Considerations (cont.) Consumers must be notified before a water system begins chloramination so that, if necessary, corrective action at point of use can be taken to minimize any risks to sensitive users. Chloramines are more difficult to remove, and ammonia can adversely affect patients receiving kidney dialysis Ammonia is toxic to aquarium fish.

10 History of Chlorine Usage First used to disinfect water mains in the UK in 1897 after an outbreak of typhoid Introduced in the United States in the early 1900 s Credited with reducing the incidence of: -cholera by 90% -typhoid and leptospirosis by 80% -amoebic dysentery by 50% Most widely used chemical for disinfection in the United States

un-reacted chlorine will react with organic material, including

11 Adding Chlorine to Water Meeting the Demand Reaction 1: Iron, manganese, or hydrogen sulfide present Reaction 2: Next, any un-reacted chlorine will react with organic material, including bacteria These reactions satisfy the natural chlorine demand of the water

12 Residual Chlorine Standard procedure to add excess chlorine to allow for a residual amount in the water to retard microbial growth in the distribution system Cl 2 Dose - Demand = Cl 2 Residual 2.50 mg/l mg/l = 2.30 mg/l

13 Free Chlorine Cl 2 + H 2 O HOCl + H + + Cl - This reaction produces free chlorine, when measuring a free Cl 2 residual. HOCl = hypochlorous acid.is being measured

14 Free Chlorination (Cont.) Cl 2 + H 2 O HOCl + H + + Cl - Free chlorine is a strong oxidizing agent Reacts with a wide variety of compounds Therefore, not very persistent

15 Chloramination Ammonia can occur naturally in a body of water or be added to drinking water as aqueous ammonia, ammonia gas or ammonia salts.either way, the ammonia reacts with chlorine to form chloramines

16 Chloramination Adding chlorine to water yields Cl 2 + H 2 O HOCl + H + + Cl - NH3 Ammonia reacts with hypochlorous acid, to produce a desirable, combined form of chlorine called monochloramine

17 Conditions for this Reaction NH 3 + HOCl NH 2 Cl + H 2 O The reaction of the hypochlorous acid and ammonia will convert practically all the free chlorine to monochloramine in under 1 second when ph is near 8, temperature is near 25 degrees C and the chlorine to ammonia weight ratio is near 5 : 1

18 Ratio? What s the Big Deal The weight ratio of Cl 2 to NH 3 directly affects the type of chloramine formed. Under normal chloramination conditions, the Cl 2 : NH 3 ratio can range from 3 : 1 to 5 : 1, causing monochloramine to be the dominant species formed. Ratios greater than 5 : 1 favor the formation of di-chloramine due to the reaction of excess hypochlorous acid with monochloramine

19 Ratio Calculation The standardized method for determining the chlorine to ammonia ratio is: Chloramine residual (mg/l as Cl 2 ) divided by Ammonia residual (mg/l as N) PWD (typically) 2.30 mg/l as Cl 2 / 0.50 mg/l NH 3 -N = 4.6

20 Ratio Ideally, 1 molecule of Cl 2 combines with 1 molecule of NH 3 All Cl 2 and NH 3 molecules are combined Nothing left over, no free Cl 2 or NH 3 A 1 : 1 ratio, based on # of molecules.but what about weight

21 Where Does the Weight Ratio Come From? Individual atoms have weight or mass Therefore, groups of atoms, or molecules, can be weighed

22 Chemistry of chloramination To fully understand the chemistry involved with chloramination, it is helpful to start with the basics:

23 Elements Have Mass

24 Weight Ratio Cl weighs ~ 35. Since chlorine atoms occur in pairs as Cl 2, the total weight is ~ 70 Ammonia is measured as N (which is why it is expressed as NH 3 -N). Nitrogen, N, weighs 14 The ratio between the weights is: 70 / 14 = 5.0

25 Cl 2 and NH 3 at 5:1 Dosing 3 chlorines into the water followed by 3 ammonias. Each chlorine will react with one ammonia to form a monochloramine molecule. Cl 2 HOCl + NH 3 = NH 2 Cl Water flow Cl 2 HOCl + NH 3 = NH 2 Cl Cl 2 HOCl + NH 3 = NH 2 Cl Perfect

26 Di and Trichloramine compounds During monochloramine formation, an excess of chlorine can result in the unintended formation of di and trichloramine compounds NH2Cl + HOCl NHCl2 (dichloramine) + H2O NHCl2 + HOCl NCl3 (trichloramine) + H2O

Ratio greater than 5 : 1 HOCl NH 3 NH 2 Cl Water flow HOCl + NH

27 Overfeeding Chlorine Ratio Too High What if too much chlorine is added (or too little ammonia)? Ratio greater than 5 : 1 HOCl NH 3 NH 2 Cl Water flow HOCl + NH 3 = NH 2 Cl HOCl NH 3 NH 2 Cl NHCl 2 = NHCl 2 HOCl HOCl HOCl NHCl 2 di-chloramine; undesirable T & O

Ratio less than 5 : 1 HOCl NH 3 NH 2 Cl Water flow HOCl + NH 3

28 Underfeeding Chlorine Ratio Too Low What if too little chlorine is dosed (or too much ammonia? Ratio less than 5 : 1 HOCl NH 3 NH 2 Cl Water flow HOCl + NH 3 = NH 2 Cl HOCl NH 3 NH 2 Cl NH 3 NH 3 NH 3 Free ammonia; > 0.10 mg/l fuels nitrification in DS

29 Chloramination Trade off BENEFITS Less potential for DBP s (THM s HAA s) Longer lasting residual Lower taste/odor threshold than free Cl 2 CHALLENGES Monochloramine 4x weaker biocide than free Cl 2 takes more of it (2.0 vs 0.5 mg/l) More to think about, i.e feed pumps, ratio Nitrification

This process eliminates ammonia, as it creates the nitrite necessary for the next step.

30 Nitrification A Biochemical Process Free ammonia fuels the nitrification process. Bacteria (AOB) oxidize the ammonia and produce nitrite, NO 2. This process eliminates ammonia, as it creates the nitrite necessary for the next step. Bacteria (NOB) then oxidize nitrite into nitrate, NO 3 and nitrogen gas N 2 Free Ammonia NH3 Nitrite NO2 Nitrate NO3

31 Conditions for Nitrification The main contributing factors include: Excess ammonia in the distribution system Presence of nitrifying bacteria Warm water temperatures (15 C and higher) Long detention times (excessive water age) Low disinfectant residuals to combat nitrifiers

32 Impacts of Nitrification Rapid chloramine loss Decrease in ph Elevation of nitrite, nitrate and HPC For example, a 0.40 mg/l nitrite concentration will consume 2.0 mg/l of the chloramine residual. The depletion of chloramine residuals could leave a system vulnerable to bacteriological contamination.

33 Nitrification Control Measures Monitor ratio and free ammonia at POE Flushing program Exercising tanks/reservoirs Moving water through system quickly Free chlorine boost to recombine free NH 3 Periodic switch to free Cl 2, or breakpoint chlorinating

34 Breakpoint phenomena

35 Long Term Control What Does AWWA Say? limiting the amount of free ammonia available in the treatment plant finished water is a valid practice and one that utilities should pursue.

36 Wrap up Valid reasons to switch to chloramination, must consider many things Process must be monitored at the POE as well as the DS for effectiveness Nitrification is a real concern but can be managed successfully

37 References Connell, G. F., The Chlorination/ Chloramination Handbook. American Water Works Association. Water Disinfection Series. Fundamentals and Control of Nitrification in Chloraminated Drinking Water Systems American Water Works Association. Manual of Water Supply Practices, M56. 1st ed.

38 Questions Contact info: Michael Koza Regulatory/Security Advisor Portland Water District (207)

Science of Chloramination. Maine Water Utilities Association June 8, 2010

Science of Chloramination. Maine Water Utilities Association June 8, 2010 Science of Chloramination June 8, 2010 What is chloramination? Chloramination is the process of disinfecting water using chloramines, compounds of chlorine and ammonia. The use of chloramines in the United