CHLORAMINATIONAND

CHLORAMINE ANALYSIS

SW AWWA 2014

COMBINED CHLORINE - CHLORAMINATION

• Chlorine (HOCl and OCl-) reacts with ammonia to form chloramines, commonly referred to as ‘combined chlorine’

• The predominate species are monochloramine and dichloramine. A small fraction is trichloramine or nitrogen trichloride

2

BREAKPOINT CURVE

Chlorine Added

Tota

l Chl

orin

e Re

sidu

al

Brea

kpoi

nt

Total residual chlorine, primarily monochloramine

Free residual chlorine

Cl2:N < 5:1, typical

Cl2:N > 5:1, typical

Cl2:N > 9:1, typical

3

BREAKPOINT CURVE CONSIDERATIONS

• Shape of the curve is dependent upon – amount of ammonia and other chlorine demand substances in the water– temperature– pH– contact time

• Most effective disinfection, least taste and odor occurs with free residual chlorine

• Free chlorine may lead to formation of DBP

4

CHLORAMINATION

• Chloramination: Purposeful use of chlorine and ammonia to form monochloramine.

– Minimizes formation of chlorinated organics

– Ammonia to chlorine Ratio is controlled to favor formation of monochloramine, typically 5:1 Cl2:N

• Total residual chlorine test: All free and combined chlorine species

5

CHLORAMINES

• Less effective disinfection than free chlorine. HOCl is 25X more effective biocide

• Chloramines require longer contact time and/or greater concentration than free chlorine.

• Possible taste and odor (dichloramine)

• More stable than free chlorine (long distribution systems)

• Generally do not produce DBP (NH2Cl may form DBP – NDMA being studied)

6

CHLORAMINE FORMATION

• Monochloramine - NH2Cl

NH3 + HOCl NH2Cl + H2O

• Dichloramine - NHCl2NH2Cl + HOCl NHCl2 + H2O

• Tricholoramine (Nitrogen Trichloride) - NCl3NHCl2 + HOCl NCl3 + H2O

• Chloramines are not as effective disinfectants as free chlorine

7

DEFINITION OF UNREACTED AMMONIA

• Ammonia in solution as

– NH3 Free ammonia gas dissolved in water or;

– NH4- The ammonium ion

8

• What are chloramines?• Where are chloramines used?• Chlorine and Ammonia• Chloramination Objectives• The Dance of Chlorine and Ammonia• Building the Chloramination Curve• Preventing Nitrification

ClCl

Cl

HHN

HHH

N

WHAT ARE CHLORAMINES?

• The word “chloramines” describes the group of three compounds formed by mixing chlorine and ammonia together– Monochloramine – ideal form for drinking water treatment– Dichloramine– Trichloramine

Cl

HH

N

WHERE ARE CHLORAMINES USED?• Chloramines are used in drinking water as an alternative to

the more aggressive disinfection of chlorine – Chlorine reacts quickly with organic materials present in source water,

which can cause the formation of undesirable disinfection by products (DBPs) that are regulated by the EPA

– Monochloraminei. Is less reactive than chlorineii. Is a weaker disinfectant than chlorineiii. Requires a longer contact time than chlorineiv. Does not form DBPsv. Is more stable and maintains a longer residualvi. Formation is a complex process

CHLORINE AND AMMONIA• Chlorine

– When mixed with water, chlorine forms hypochlorous acid and hypochlorite

CHLORINE(Cl2 )

HYPOCHLOROUS ACID (HOCl)

HYPOCHLORITE (OCl-) ++ WATER

(H2O)

Cl Cl

CHLORINE AND AMMONIA• Ammonia

– When hypochlorous acid is mixed with ammonia, chloramines are formed

- MONOCHLORAMINE (NH2Cl)

HYPOCHLOROUS ACID + AMMONIA - DICHLORAMINE (NHCl2)

(HOCl) (NH3) - TRICHLORAMINE (NCl3)

HHH

N

• Blend Chlorine and Ammonia together in a 1:1 molar ratio– The goal is to exclusively form

monochloramine– Inhibit and/or eliminate the

formation of dichloramine and trichloramine

• Dichloramine and trichloramine are unstable, and create taste and odor problems

– Minimize the introduction of significant amounts of free ammonia in the distribution system

• Excess free ammonia will promote the growth of bacteria and biofilms, and can lead to nitrification in the distribution system

CHLORAMINATION OBJECTIVES

NOMNATURALLY ORGANIC

MATTER

15

USED WITH PERMISSION, GOLDEN STATE WATER

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0 5 10 15 20 25 30

Chlorine Added (mg/L)

Tota

l Chl

orin

e (m

g/L)

Total CL 1 min Total CL 10 min Total CL 60 min Total CL 360 min

> 6:1

> 14:1

16

00.10.20.30.40.50.60.70.80.9

11.11.21.31.4

0 5 10 15 20 25 30

Free

Am

mon

ia (m

g/L)

Chlorine Added (mg/L)

1 min 10 min 60 min 360 min

Breakpoint chlorination dose of 16.4 mg/L is needed for complete removal of free ammonia

USED WITH PERMISSION, GOLDEN STATE WATER17

NITRIFICATION IN THE DISTRIBUTION SYSTEM

NH3/NH4+ + NO2

- + NO3-NH2Cl +

Disinf ▼f-NH3 ▲

pH ▼DO ▼NO2

- ▲Alk ▼

pH ▼DO ▼NO3

- ▲Alk ▼

Circular Problem

Sloughing of biofilm causes Turbidity ▲ Flow ▼HPC ▲

Customer Complaints

▲

Distribution System

NITRIFICATION

• Conversion of ammonia to nitrites and nitrates

– NH3 + O2 NO2-+ 3H+ + 2e-

– Nitrosomonas Nitrosococcus, and Nitrosospira.

• Conversion of nitrite to nitrate

– NO2- + H2O NO3

- + 2H+ +2e-

– Nitrobacter Nitrospina, Nitrococcus, and Nitrospira

19

INDICATION OF NITRIFICATION

Chloramine residual

Free Ammonia

Temperature

Dissolved Oxygen

pH and/or alkalinity

HPC

NO2/NO3

20

CONTROL STRATEGIES FOR DISCUSSION

pH

Free ammonia

Water age

Chloramine residual

Light

TOC

Tank Mixing

21

NITRIFICATION

Nitrifying bacteria feed on ammonia…

producing Nitrites…which exert a chlorine demand…

which decreases the residual…which allows microbes to flourish…

to produce more nitrites…which continues the spiral…

until your residual is gone!aka … “feeding the beast”

THE DANCE OF CHLORINE AND AMMONIA

• Chlorine and Ammonia are not well suited to each other for reaction.– HOCl is favored at lower pH– NH3 is favored at higher pH– “Compromise” used is usually around pH 8-8.3.

• One ammonia molecule and one chlorine molecule are required to form monochloramine:– “Easy” in the laboratory, but what about:

• Ammonia in sourcewater• Variable chlorine demand in sourcewater

REACTION - FREE CHLORINE:

Cl2 + H2O HCl + HOCl

HOCl H+ + OCl-

HOCl + OCl- + DPD Red complex (530 nm)Read as soon as possible after 20 sec mix.

Reaction - Total Chlorine:

HOCl + OCl- + Chloramines + KI + DPD

HOCl + OCl- + I2 + DPD Red complex

Read at 530 nm.

Read after 3 to 6 minutes.

MONOCHLORAMINE AND FREE AMMONIA

• Method is designed for one sample. Note that 2 different programs (curves) are used. Presume cells are matched.

• Plan your timing well, as there are 2 five minute reaction periods.– Program 66 for Monochloramine– Program 388 for Free Ammonia– The chemistry “makes monochloramine by chlorinating

free ammonia”• The powder reagent only reacts with monochloramine

(M vial)• The liquid reagent is chlorine and reacts with any free

ammonia, making additional monochloramine (FA vial)• By zeroing out the monochloramine, the free ammonia

can be determined by difference

MONOCHLORAMINE AND FREE AMMONIA

• How it works:– The powder chemistry reacts with

monochloramine and forms a proportional green color (the M vial).

– The liquid reagent contains chlorine which converts any free ammonia to additional monochloramine (the FA vial).

– The difference between the 2 measurements is equal to the free ammonia, if any.

– A great tool for any chloraminating system (DW and WW).

BREAKPOINT CHLORINATION CURVE

I II III

Ideal zone for DW disinfection

CHLORAMINATION MONITORING & CONTROL

• Parameters– Monochloramine– Ammonia– Total Chlorine– Free Chlorine

• Data from each of the parameters above can help determine where water is on the breakpoint curve

HO

Cl

• If the plant does a test for total chlorine, and obtains a result of 3 mg/L…– Total chlorine = 3.0 mg/L

• Where on the breakpoint curve are they?– What part of the curve makes a significant difference

CHLORAMINATION MONITORING & CONTROL

I II III

Where is 3 mg/L Total Chlorine?

3 mg/L

• Laboratory Tests– Monochloramine and free ammonia with Monochlor-F reagent

• Colorimetric method• One method sequentially determines monochloramine and free ammonia • Can be run on spectrophotometers and some colorimeters• Indophenol chemistry

– Free Chlorine/Total Chlorine– DPD colorimetric method– Chloramine can produce false positive results– Autocat 9000 Autotitrator for chlorine

– Ammonia– ISE (ion selective electrode)– Colorimetric ammonia test

CHLORAMINATION MONITORING & CONTROL

• Based on data from other tests, the analyst/operator will be able to tell where they are on the breakpoint curve

CHLORAMINATION MONITORING & CONTROL

Zone IIMonochloramine < Total Cl2

Free Ammonia = 0

Zone 1Monochloramine = Total Cl2

Free ammonia > 0

Zone IIITotal Cl2 > 0

Free Ammonia = 0Monochloramine = 0

• Total Chlorine• Free Chlorine• Monochloramine• pH• Alkalinity• Nitrate/Nitrite• DO

• HPC• ATP• DBP• Nitrifying Bacteria• Temperature

CHLORAMINATION MONITORING & CONTROL

CHLORAMINATIONAND

CHLORAMINE ANALYSIS

HACH TRAINING ACADEMYDRINKING WATER COURSE