Online Monitoring Chloramination Process Presented at OAWWA NE District Meetings May 3, 2018 Wei Zhang and Scott Kahle ASA Analytics Waukesha, WI 53186 Technical Sources Optimizing Chloramine Treatment AWWA Research Foundation 1993 and 2004 Laboratory Experiments and Experiences at Hundreds Chloramination Facilities using ChemScan chloramination Analyzers Chlorination 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 Potential taste and odor issues Under some conditions, decays rapidly Disinfection Byproducts - DPBs Hypochlorous Natural Organic THM and HAA Acid (HOCl) Matter (NOM) (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 Odor Weak Disinfectant) Dichloramine + HOCl NCl3 + H20 Trichloramine (Strong Odor 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 Di-chloramine and Tri-chloramine are not produced) Disinfection Byproducts Natural Organic Minimal DBPs Monochloramine Matter (NOM) + + 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, Ontario, Canada 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 1.0 mg/L NH3-N, pH 7, temperature 25 C, contact 2 hours Zone 1 Zone 2 Zone 3 Zone 4 Available Residual Chlorine (mg/L) Chlorine Residual Available Applied Chlorine Dosage (mg/L) The Dreaded “Breakpoint Curve” 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 Molecular: 1 1 Weight: 1 5 Zone 1 Zone 2 Zone 3 Zone 4 • Zone 3: As the ratio exceeds 5:1, no free ammonia available - • Di-chloramines and Tri-chloramines are formed 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 Nitrification Ammonia Oxidizing Nitrite Oxidizing Ammonia Bacteria (AOB) Nitrite Bacteria NH3 Nitrate Nitrosomonas NO2 Nitrobacter NO3 + Dissolved Dissolved Oxygen O2 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 Online Analyzer - 1 How about using 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 On-Line Analyzer - 2 Multiple Chloramination Parameter 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 Why is Chloramination so Difficult? Varying NH3-N, pH 7, temperature 25 C, contact 2 hours Available Residual Chlorine (mg/L) Chlorine Residual Available Applied Chlorine Dosage (mg/L) Simplified Drinking Water Process Post Chlorination Ammonia Feed Cl2 Cl2 FNH3, TNH3, Mono Total Cl2 Analyzer Analyzer and TCl2 Analyzer Goal 3.0 mg/L Wet Well Mixer Free NH3-N 0.050.220.14 mg/L Cl2 Cl NH 2 3 Weight Ratio Feed Trim Feed Free Cl2 Cl2 : NH3-N 3.0 mg/L 3.44.8:13.7:14.2:1 : 1 Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 3.0 :1 2.5 1 2 0.8 FNH3 0.22 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.99 mg/L 0.5 0.2 Mono 2.90 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 2.94 mg/L Actual Cl2:N Ratio DIChor 0.04 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 3.73.4:1 :1 2.5 1 2 0.8 FNH3 0.11 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.77 mg/L 0.5 0.2 Mono 2.89 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 2.93 mg/L Actual Cl2:N Ratio DIChor 0.04 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 3.4:14.6:1 2.5 1 2 0.8 FNH3 0.04 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.64 mg/L 0.5 0.2 Mono 2.93 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 2.97 mg/L Actual Cl2:N Ratio DIChor 0.04 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 3.4:15.0:1 2.5 1 2 0.8 FNH3 0.02 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.59 mg/L 0.5 0.2 Mono 2.9 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 2.97 mg/L Actual Cl2:N Ratio DIChor 0.07 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 3.4:16.3:1 2.5 1 2 0.8 FNH3 0.02 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.44 mg/L 0.5 0.2 Mono 2.38 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 2.79 mg/L Actual Cl2:N Ratio DIChor 0.41 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 3.4:16.5:1 2.5 1 2 0.8 FNH3 0.02 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.27 mg/L 0.5 0.2 Mono 1.33 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 1.74 mg/L Actual Cl2:N Ratio DIChor 0.27 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 7.73.4:1 :1 2.5 1 2 0.8 FNH3 0.02 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.02 mg/L 0.5 0.2 Mono 0.13 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 0.16 mg/L Actual Cl2:N Ratio DIChor 0.03 mg/L Free Cl Breakpoint with Fixed Cl2 2 Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 3.0 mg/L Varying NH3 Free NH3 Total N 3.5 1.4 Ratio 3 1.2 8.83.4:1 :1 2.5 1 2 0.8 FNH3 0.02 mg/L 1.5 0.6 Cl2 mg/l NH3 mg/l 1 0.4 TNH3 0.02 mg/L 0.5 0.2 Mono 0.14 mg/L 0 0 3.0 3.7 4.6 5.0 6.3 6.5 7.7 8.8 TCl2 0.74 mg/L Actual Cl2:N Ratio DIChor 0.03 mg/L Optimal Control Fixed Cl2 3.0 mg/l Mono Cl2 Total Cl2 DI Cl2 Varying NH3 Free NH3 Total N 3.5 1.4 3 1.2 2.5 1 2 0.8 1.5 0.6 Cl2 mg/l NH3