Chlorination-Chloramination[1]

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CHLORINATIONCHLORINATION

Chlorination Curve

• What happens when chlorine is added to water?– A chlorination curve will help describe what

happens during this process

Chlorination Curve

• What is a chlorination curve?– A graph of the amount of chlorine measured

in a solution versus the amount of chlorine added

Chlorination Curve

Chlorine Added

Chlorination Curve

• Begin adding chlorine to water– Chlorine will first react to exhaust chlorine

demand in the system– Chlorine added will not be recovered in a

chlorine test

Chlorination Curve

Chlorine Added

Chlorination Curve

• Continue adding chlorine to the system– Once chlorine demand is exhausted,

additional chlorine added will be recovered in a chlorine test

Chlorination Curve

Chlorine Added

Chlorine Testing

• Chlorine - Free & Total– DPD chlorine reagent powder pillows or

AccuVacs (EPA approved)• Pocket Colorimeter II• DR/800• DR/2800• DR/5000

CHLORAMINATIONCHLORAMINATION

Chloramines

• Chloramines are formed when free chlorine reacts with free ammonia present in the water – Monochloramine (NH2Cl)– Dichloramine (NHCl2)– Trichloramine (NCl3)

Chloramination Curve

Chlorine Added

• Begin adding chlorine to a water containing ammonia– Initial addition of chlorine reacts to exhaust

any chlorine demand present in the water

Chlorination Curve

Chlorine Added

• Continue to add chlorine to the water– After chlorine demand is exhausted, chlorine

reacts with ammonia to form monochloramine

HOCl + NH3 NH2Cl + H2O

Chlorination Curve

Chlorine Added

ChloraminationChloramination

5:1 Cl2:N Ratio

• Continue to add chlorine to the water– After complete formation of monochloramine,

monochloramine reacts with additional chlorine to form dichloramine and nitrogen trichloride.

HOCl + NH2Cl NHCl2 + H2O

• Continue to add chlorine to the water– As dichloramine and nitrogen trichloride form,

the addition of chlorine continues to oxidize these compounds to nitrogen gases

Chlorination Curve

Chlorine Added

Breakpoint 9:1 Cl2:N Ratio

5:1 Cl2:N Ratio

• Continue to add chlorine to the water– After the breakpoint, all chlorine added to the

water remains as free chlorine– Breakpoint chlorination

Cl2 + H2O HOCl + OCl-

Chlorination Curve

Chlorine Added

Breakpoint 9:1 Cl2:N Ratio

5:1 Cl2:N Ratio

Free ChlorinationFree Chlorination

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Chloramination Goals

• Complete formation of monochloramine (stay in section I)– 3-5:1 Cl2:N optimal feed ratio

• Avoid dichloramine formation– Avoid taste and odor problems

• Minimize un-reacted ammonia– Control biofilm and nitrification

Chloramination Species

Chlorine Added

II IIII

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Total Chlorine

Free Ammonia

Chlorine Added

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Total Chlorine

Free Ammonia

Monochloramine

Chlorine Added

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Total Chlorine

Free Ammonia

Monochloramine

Free Chlorine

• Continue to add chlorine to the water– The point at which all dichloramine is

converted to nitrogen gas is the breakpoint.

Where Am I When Total Chlorine = 3mg/L?

Chlorine Added

II IIII

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I Am Here!

Chlorine Added

II IIII

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Mono = Total Cl2Mono = Total Cl2

Free Am > 0Free Am > 0 Mono < Total Cl2Mono < Total Cl2

Free Am = 0Free Am = 0

Total Cl2 > 0Total Cl2 > 0Mono = 0Mono = 0

Free Am = 0Free Am = 0

Ammonia/Monochloramine Relationship

0 2 4 6 8 10 12

Chlorine Dose, mg/L

Results as NResults as N““tt--NHNH33NN””

NHNH22Cl (N)Cl (N)

ff--NHNH33NN BreakBreak--pointpoint

Chlorination-Chloramination[1]

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