Chloramination 101 Scott Kahle ASA Analytics

Optimizing Chloramine Treatment AWWA Research Foundation Technical Sources Optimizing Chloramine Treatment AWWA Research Foundation 1993 and 2004 AWWA and EPA Web sites Laboratory Experiments and Experiences at Hundreds Chloramination Facilities

Chlorination + + Chlorine Pathogens Safe Water Chlorine Hypochlorous Acid + + Hypochlorite Chlorine has prevent the spread of waterborne diseases such as cholera, dysentery, typhoid etc ….

Chlorination First use for Water Disinfection in late 1800’s Benefits: Strong oxidizer for disinfection Persistent residual to the tap Disadvantages: Strong oxidizer that reacts with many inorganics and organics Under some conditions, decays rapidly

Disinfection Byproducts - DPBs Hypochlorous Acid (HOCl) Natural Organic Matter (NOM) THM and HAA (Carcinogens) + + Strong Oxidizer

DBP Reduction Remove Organic Precursors that are reactive with chlorine (filters, membranes, ion exchange, etc… remove TOC ) Decrease the amount of hypochlorous acid available in the reaction (this can be accomplished via chloramination) Decrease the time of contact between the organic material and hypochlorous acid (also accomplished via chloramination)

Chloramine Formation NH3 + HOCl NH2Cl + H20 Monochloramine Monochloramine + HOCl NH2Cl + H20 Dichloramine (Strong Order Weak Disinfectant) Dichloramine + HOCl NCl3 + H20 Trichloramine (Strong Order and Taste Weak Disinfectant) Organo-chloramines are can also be formed in the presences of organics

Chloramines vs Chlorine More Stable - Longer Lived Residuals Less Reactive (reduced DBP formation) Minimizes Objective Taste and Odor (As long as Dichloramine and Trichloramine are not produced)

Disinfection Byproducts Natural Organic Matter (NOM) Minimal DBPs Monochloramine + + Weaker Oxidizer

History of Chloramines Initially used in the early 1900s when it was found that chlorine-ammonia addition could save cost by reducing chlorine used. First recognized Chloramination WTP in North America – Ottawa, Ont. In 1916. First US Chloramination WTP – Denver, Colorado in 1917 to improve taste.

History of Chloramines (Cont.) By 1938 – more than 400 utilities chloraminating. Practice reduced during WWII due to shortage of ammonia. 1970s – THMs were discovered to be a health threat. Chloramines used to reduce THM formation. Regulations balancing risk from microbial contamination and risks of disease from DPBs. 1998 Stage 1 Disinfectant/DBP Rule 2006 Stage 2 Disinfectant/DBP Rule

Conversion to Chloramination at Some Cities (approx) Denver, CO 1917 Portland, OR 1924 Massachusetts Water Resources Authority 1932 St. Louis, MO 1934 Portland, ME 1938 Boston, MA 1944 Minneapolis, MN 1954 Dallas, TX 1959 Kansas City, MO 1964 Miami, FL 1982 San Diego, CA 1982 Currently more than 1500 Utilities use chloramination in the U.S.

Chloramination Basics Applied Chlorine Dosage (mg/L) Zone 1 Zone 2 Zone 3 Zone 4 1.0 mg/L NH3-N, pH 7, temperature 25 C, contact 2 hours Available Residual Chlorine (mg/L) The Dreaded “Breakpoint Curve”

Relative Chlorine Demand of Some Compounds: Zone 1 Zone 2 Zone 3 Zone 4 Zone 1: Initial chlorine demand is met: Chlorine is oxidizing reactive chemical constituents. Relative Chlorine Demand of Some Compounds: Fe = 0.64 mg/l NH3 = 12.00 mg/l Mn = 1.30 mg/l Org-N = 1.00 mg/l NO2 = 5.00 mg/l TOC = 0.10 mg/l

Zone 1 Zone 2 Zone 3 Zone 4 Zone 2: Chloramines are forming up to an approximate ratio of 5:1 (Five Parts Chlorine to One Part Ammonia by weight). NH3 + HOCl NH2Cl + H20 Monochloramine Weight: 1 5

Zone 1 Zone 2 Zone 3 Zone 4 Zone 3: No free ammonia available - Dichloramines and Trichloramines are formed as the ratio exceeds 5:1 NH2Cl + HOCl NHCl2 + H2O Dichloramine NHCl2 + HOCl NCl3 + H2O Trichloramine

Zone 1 Zone 2 Zone 3 Zone 4 Zone 4: Breakpoint - Free chlorine residual is now being created. For every 1.0 mg/l of chlorine added, the residual will increase 1.0 mg/l. Some Organo-chloramines and Trichloramine still exist.

How Fast Are Chloramines Made? pH Time (Seconds) 4 147 7 0.2 8.3 0.069 12 33.2

Chloramine Species with pH

Cl2:N Ratio Effects on THM and Flavor

Optimal Chloramination Control Range This graph represents the optimal control range of monochloramine when comparing it to the formation of flavor and total trihalomethanes. The upper graph is the breakpoint curve. As we get to the peak of that curve it is at a point where we have very little free ammonia and also our flavor and trihalomethanes formation is at a minimum.

Nitrification + + Ammonia Oxidizing Bacteria (AOB) Nitrosomonas Nitrite Oxidizing Bacteria Nitrobacter Ammonia NH3 Nitrite NO2 Nitrate NO3 + Dissolved Oxygen O2 Dissolved Oxygen O2 +

Nitrification Impact Nitrification occurs when disinfection concentration is low. It can result in a lowering of pH, increased corrosion and/or depletion of Dissolved Oxygen. For every 1.0 mg/l of NO2 (Nitrite) formed, 5.0 mg/l of chlorine are needed to oxidize. Nitrification typically results in the further reduction disinfection residual causing a downward spiral.

Nitrification Control Maintain Higher Chloramine Residual Higher Cl2 : NH3-N Ratio (less Free NH3) Maintain Higher pH Periodic Chlorine Shocks Higher Turnover and/or Mixing in Reservoirs System Flushing Monitoring at Strategic Locations and Boost Chlorine

Chloramination Control Challenges Maintain Adequate Disinfectant Concentration to Ensure Safe Water Feed Enough Ammonia to Prevent Di and Trichloramine Formation and Prevent Drop in Chlorine Residual Prevent Over Feed of Ammonia to Minimize the Potential of Nitrification in the Reservoirs and Distribution System On-Line Analysis Provides the Information Required to Control the Chloramination Process

Breakpoint as Measured by Free and Total Chlorine Analyzers A Total Chlorine result has 3 possible locations on the breakpoint curve Free Chlorine test reacts with Monochloramine giving a false reading until beyond the Breakpoint First Indication of Free Chlorine is AFTER Dichloramine Formation Some municipalities attempt to use free and total chorine analyzers to control their chloramination process – with limited success. A total chlorine analyzer results in three possible locations on the breakpoint with no indication of which you are at. Free chlorine reacts with monochloramine giving false reading until beyond the breakpoint. First indication of free chlorine is after dichloramine formation.

Break-point Curve as Read on On-Line Analyzer At ratios below 5:1, Total Chlorine and Monochloramine values are equivalent Between the ratios of 5:1 and 8:1, Total Chlorine is greater than Monochloramine as Dichloramine is formed At ratio greater than 8:1, Free Chlorine is present At ratios below 5:1, Total Ammonia remains constant as Free Ammonia decreases until reaching 5:1 At ratios greater than 5:1, Total Ammonia decreases and free ammonia is near zero Here is the breakpoint curve as read on the ChemScan Analyzer In this case a .6 mg per leader ammonia sample was dosed with increasing levels of chlorine. At ratios below 5:1, Total Chlorine and Monochloramine values are equivalent Between the ratios of 5:1 and 8:1, Total Chlorine is greater than Monochloramine as Dichloramine is formed At ratio greater than 8:1, Free Chlorine is present At ratios below 5:1, Total Ammonia remains constant as Free Ammonia decreases until reaching 5:1 ratio At ratios greater than 5:1, Total Ammonia decreases and free ammonia remains near zero

Why is Chloramination so Difficult? Applied Chlorine Dosage (mg/L) Varying NH3-N, pH 7, temperature 25 C, contact 2 hours Available Residual Chlorine (mg/L)

Simplified Drinking Water Process Post Chlorination Ammonia Feed Cl2 Analyzer Cl2 Analyzer FNH3, TNH3, Mono and TCl2 Analyzer Total Cl2 Goal 3.0 mg/L Wet Well Mixer Free NH3-N Cl2 Feed 0.05 mg/L 0.14 mg/L 0.22 mg/L Cl2 Trim NH3 Feed Weight Ratio Cl2 : NH3-N Free Cl2 3.0 mg/L 4.8:1 3.4 : 1 3.7:1 4.2:1

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.0 :1 FNH3 0.22 mg/L TNH3 0.99 mg/L Mono 2.90 mg/L TCl2 2.94 mg/L DIChor 0.04 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 3.7 :1 FNH3 0.11 mg/L TNH3 0.77 mg/L Mono 2.89 mg/L TCl2 2.93 mg/L DIChor 0.04 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 4.6:1 FNH3 0.04 mg/L TNH3 0.64 mg/L Mono 2.93 mg/L TCl2 2.97 mg/L DIChor 0.04 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 5.0:1 FNH3 0.02 mg/L TNH3 0.59 mg/L Mono 2.9 mg/L TCl2 2.97 mg/L DIChor 0.07 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 6.3:1 FNH3 0.02 mg/L TNH3 0.44 mg/L Mono 2.38 mg/L TCl2 2.79 mg/L DIChor 0.41 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 6.5:1 FNH3 0.02 mg/L TNH3 0.27 mg/L Mono 1.33 mg/L TCl2 1.74 mg/L DIChor 0.27 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 7.7 :1 FNH3 0.02 mg/L TNH3 0.02 mg/L Mono 0.13 mg/L TCl2 0.16 mg/L DIChor 0.03 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Breakpoint with Fixed Cl2 Free Cl2 3.0 mg/L Ratio 3.4:1 8.8 :1 FNH3 0.02 mg/L TNH3 0.02 mg/L Mono 0.14 mg/L TCl2 0.74 mg/L DIChor 0.03 mg/L Here is a breakpoint curve where the chlorine is fixed and the ammonia is varied. In this case we’ve chosen a 3mg per liter chlorine dosage and the ammonia is decreased in prepared samples. While the ratio is less than 5:1 the total chlorine and monochloramine are equivalent until while we reach the 5:1 ratio where they begin to separate as dichloramine is forming. The total ammonia decreases as the graph goes from left to right indicating the dosage of the total ammonia. The free ammonia begins at an elevated level and decreases to near zero at the 5:1 ratio.

Optimal Control

Chloramination Control Strategies Ratiometric control Cl2 : NH3-N ratio between 3:1 and 5:1 Measures total chlorine from all forms and total ammonia from all forms (free and combined) Residual control Maintain target monochloramine or total chlorine Maintain small free ammonia residual

Chloramination Feed Options Post Chlorination Ammonia Feed Cl2 Analyzer Cl2 Analyzer FNH3, TNH3, Mono and TCl2 Analyzer Wet Well Mixer Cl2 Feed Cl2 Trim NH3 Feed

Chloramination Feed Options Simultaneous Chlorine Ammonia Feed NH3 Feed FNH3, TNH3, Mono and TCl2 Analyzer FNH3, TNH3, Mono and TCl2 Analyzer Wet Well Mixer Mixer Cl2 Boost (Optional) Cl2 Feed

On-Line Chloramination Analyzers ChemScan UV-Series – FNH3, TNH3, Mono, TCL2 and UV254 Multiple Sample Lines ChemScan Multi-mini - FNH3, TNH3, Mono and Ratio ChemScan Single Parameter - mini-FNH3, mini-TNH3, mini-Mono and mini-Chlor

Case Study I Full Scale Pilot Study Reservoir converted from Free Chlorine to Chloramines

Chloramination Process Out of Control Free ammonia either too high or too low Chlorine Levels unstable

Chloramination Process Out of Control When free ammonia is greater than zero, total chlorine tracks with monochloramine When free ammonia is zero, total chlorine is greater than monochloramine indicating formation of dichloramine

Chloramination Process - In Control - Free Ammonia level constantly above detection limit but low enough to reduce nitrification potential (ave 0.05 mg/L) Total Chlorine and Monochloramine are very close in value and stable

Summary Chloramines are Effective Disinfectants Chloramination can be Difficult to Control Too little ammonia cause di and trichloramine formation and loss of chlorine residual Too much ammonia can cause nitrification in reservoirs and distribution system Proper Distribution System Management starts with minimizing free ammonia at the plant Distribution System Boosting of Chlorine (and ammonia) is key to keep disinfectant concentration optimized Effective On-Line Analysis Equipment will Aid in the Control of the Chloramination Process

Questions