Chloramine Tips and Tricks for Operators

City of Concord Matt Holmes WTP Operator

Marco Philippon WTP Superintendent Concord’s Disinfection History

 1928 Disinfection with Free Chlorine starts.

 1974 SDWA passes, the Concord WTP is constructed, Disinfection still with Free Chlorine.

 1995 With corrosion control, and disinfection degradation in residuals at the ends of the system (nearly 150 miles of main at the time) Monochloramine added as a secondary disinfectant (1st in NH).

Intake Screens Bar rack

Primary Disinfection with Sodium Hypochlorite Disinfection Coagulant optional (Chlorine)

PH Adjustment Penacook & Fluoride Lake

Raw Water Mixing Flocculation Filtration Intake Sedimentation Clear Well (Contact Chamber) Ammonium Sulfate CO2 Addition PH Adjustment

Distribution What Operators need to know and understand

 Why the ratio is important.

 How to calculate the ratio.

 How to calculate your chemical feed rate.

 Adjust what needs to be adjusted.

 What if’s?

Why is the ratio important?

 The creation of Chloramines happens when the weight ratio of Chlorine to Ammonia (Cl2 : NH3) is between 3:1 to 5:1. Anything over 5:1 will create di- chloramine  In excess of 5:1 can lead to water quality complaints.  The ideal ratio 1 molecule of Cl2, and 1 molecule of NH3.  Chlorine weighs 5 times more than Nitrogen (70/14), hence a perfect ratio is 5:1. How to Calculate the ratio

 The standardized method for determining the chlorine to ammonia ration is:  Chlorine Residual (Free) (mg/l as Cl2)  Divided by…  Ammonia Residual (mg/l as N)

Concord (typically)  2.20 mg/l as Cl2 / 0.49 mg/l NH3-N = 4.5 How to calculate your chemical feed rate.

 Test Cl2 residual at point of injection (near).

 Test for free Ammonia (target no more than .1 mg/l)

 Perform a drawdown on Ammonia Pump. (Video)

Performing a chemical drawdown

 Equipment needed  Calibrated Column  Proper valving to isolate tank from column.  Stop watch (something that will show seconds).

 Other pertinent data:  Current flow rate in (MGD)  Chemical dosage equation

VIDEO Matt’s Calculation check

 Known:  344ml in 1 minute (results of drawdown)  1440 Minutes in a day (60min. x 24hrs)  Approx. 3785 mls per gallon

Calculating a dosage

 Known:  Water lbs/gal 8.34

 Specific Gravity PCH-180 1.26

 Solution Strength PCH 31%

 Weight/gal PCH = 8.34*1.26 = 10.50

 MGD Flow Rate 6.0 MGD

 PCH dosage 8.5 mg/l

Calculating a dosage Aqueous Ammonia

Known: Water lbs/gal 8.34

Specific Gravity Aqueous Ammonia (AA) 0.896

Solution Strength AA 29% (26 baume) Weight/gal AA = 8.34*.896 = 7.47

Assume: MGD flow rate 1.0 MGD AA dosage 0.5 mg/l

Adjust what needs to be adjusted

 Don’t get into the habit of only adjusting the Ammonia.

 Determine what your Chlorine goal is and adjust Chlorine to that.

 Then adjust your Ammonia accordingly.

The What if’s?

 What happens if the ammonia feed stops? Free Chlorine Only.

 What happens if the Chlorine feed stops? Free Ammonia Only.

 What if I have a supply chain issue? Different products. Ammonium Sulfate etc.

SL1000 Field Unit Theoretical Breakpoint Curve

(1.0 mg/L ammonia-nitrogen; pH 7; temperature 25°C)

Monochloramine Di- and Tri - Free chlorine 5 chloramines 3

2 Breakpoint

1 Total Residual (mg/L) Chlorine Residual Total

1 2 3 4 5 6 7 8 9 10 11 12 13 Chlorine Dose (mg/L) Source: Wolfe et al. 1984 Questions?