10/02/2014
Disinfection Using Chloramination
Chris Griffin
Hach Company
p y
1
BEFORE WE BEGIN…
BEGIN
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10/02/2014
Before we begin….
• Who currently
– Uses Chlorine only?
– Uses Chloramination at their water plant or in distribution?
– Uses Chloramination only in distribution?
– Controls only with bench testing?
– Controls automatically with on-line instrumentation?
• What do you want to learn and take away from this
session?
3
Summary
• Goal : Provide a more in-depth understanding of the
Disinfection Process using Chloramines. Hands-on
monochloramine testing.
• Balance is Key: Experience proves that the
chloramination process can be extremely effective, but
only if the concentration of ammonia and chlorine in the
system remains in proper balance.
• Understand the Reactions: For optimal control of the
chloramination process, understanding of the reactions
taking place and measurement of the proper parameters
can simplify operation and ensure proper disinfection
4
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10/02/2014
Take Away Messages
• Monochloramine can help reduce DBPs
• Proper measurement is the key to effective control
• Know through analysis where you are on the Chlorine
Breakthrough Curve
• Target a Cl2 to N ratio of 3-5:1 to avoid dichloramine
formation
• Minimize unreacted ammonia – free ammonia >than but
close to 0
• When making process changes
changes, change only one variable
at a time
5
Outline
• Introduction to Chloramination
• Optimizing Monochloramine Production
• Hands-on Monochloramine Testing
• Additional Related Material
–
–
–
–
Applying the Concepts
Making Adjustments
Special Situations
Determining Ammonium Feed Rate
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10/02/2014
INTRODUCTION TO
CHLORAMINATION
7
Introduction to chloramination
• Chlorination
• DBP’s
DBP’
• Alternative disinfection methods
• Chloramination monitoring
g
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10/02/2014
Chlorination
• Chlorine is the most often used disinfectant used
for water treatment
– Use began in the early 1800’s for industrial water
– Used as a disinfectant in drinking water since mid1800’s
9
Chlorination
How does chlorine react with water?
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10/02/2014
Chlorine Chemistry
• Chlorine is added to water as chlorine gas or as
sodium or calcium hypochlorite.
Chlorine Gas:
Cl  H O  HOCl  H   Cl2
2
Sodium Hypochlorite:
NaOCl  H O  Na   HOCl  OH2
11
Chlorine Chemistry
• The
two chemical species formed by chlorine in
water are hypochlorous acid and hypochlorite ion
HOCl  H   OClHypochlorous Acid
Hypochlorite Ion
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10/02/2014
Chlorine Chemistry
• Hypochlorous acid is the stronger disinfectant
• Below pH 7.5 free chlorine exists predominantly
in the HOCl form
• Above pH 7.5 free chlorine exists predominantly
in the OCl- form
OCl-
HOCl
pH 7.5
13
CHLORINATION CURVE
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10/02/2014
Chlorination Curve
• What happens when chlorine is added to water?
– A chlorination curve will help describe what happens
during
g this p
process
15
Chlorination Curve
• What is a chlorination curve?
– A graph of the amount of chlorine measured in a
solution versus the amount of chlorine added
16
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10/02/2014
Chlo
orine Measured
Chlorination Curve
Chlorine Added
17
Chlorination Curve
• Begin adding chlorine to water
– Chlorine will first react to exhaust chlorine demand in
y
the system
– Chlorine added will not be recovered in a chlorine test
18
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10/02/2014
Chlo
orine Measured
Chlorination Curve
Chlorine Added
19
Chlorination Curve
• Continue adding chlorine to the system
– Once chlorine demand is exhausted, additional
chlorine added will be recovered in a chlorine test
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10/02/2014
Chlo
orine Measured
Chlorination Curve
Chlorine Added
21
Chlorine Testing
• Chlorine monitoring points
– Monitor preoxidation (if performed)
– At time of chlorine application
– In distribution system for adequate residual
Cl2
Cl2
Cl2
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10/02/2014
ALTERNATIVE
DISINFECTANTS
23
Alternative Disinfectants - Outline
• Introduction to alternative disinfectants
• Chloramination
– Chloramination chemistry
– Chloramination curve
• Testing for disinfectants
24
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10/02/2014
Alternative Disinfectants
• What’s the problem with chlorine?
– Chlorine is very reactive with organic matter to form
halogenated
g
DBPs.
• For some systems, this poses no problems.
• For some systems, chlorine is a major contributor to a DBP
problem.
25
Alternative Disinfectants
• Alternative to chlorine which:
–
–
–
–
–
Adequately disinfects
Maintains residual
Removes taste and odor compounds
Practical
Minimizes reactions with natural organic matter that
form DBPs
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10/02/2014
Alternative Disinfectants
• The main alternative disinfectants that drinking
water plants use are chloramines and chlorine
dioxide.
• Some newer plants are also switching to:
– Ozone
• No residual, bromate by-product
– UV Disinfection
• No
N residual,
id l d
destroys
t
organic
i material
t i l
• Ozone or UV are rarely used due to the cost of
treatment
27
Chloramines
• Chloramines are formed when free chlorine
reacts with free ammonia present in the water
– Monochloramine (NH2Cl)
– Dichloramine (NHCl2)
– Trichloramine (NCl3)
“GOOD”
GOOD form
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10/02/2014
Chloramination Benefits
• Reduces formation of halogenated DBPs
• Maintains
M i t i residual
id l
• More economical than alternatives
29
OPTIMIZING
MONOCHLORAMINE
PRODUCTION
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10/02/2014
Chloramination Chemistry
Free Chlorination:
Cl2 + H2O
Chloramination:
NH3 + HOCl
NH2Cl + HOCl
NHCl2 + HOCl
Organic Amines:
Org N + HOCl
HOCl + OClH2O + NH2Cl
H2O + NHCl2
H2O + NCl3
OrgN
OrgN--Cl
(strong disinfectant)
Desired form (Mono)
Increasing disinfection
efficiency, but taste and
odor problems
(~no disinfecting)
disinfecting)
32
Chloramination Chemistry
• Monochloramine is most stable, desired
• Relatively weak oxidizer compared to chlorine
– Germicidal effectiveness is a factor of 200 less
• Higher CT required
– so Chlorine added first then Ammonia
• Maintains long residual times
• Higher residual levels are required in distribution
system (2.0 mg/L – 4.0 mg/L)
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Chlo
orine Measured
Chloramination Curve
Chlorine Added
34
Chloramination Curve
• Begin adding chlorine to a water containing
ammonia
– Initial addition of chlorine reacts to exhaust any
chlorine demand present in the water
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10/02/2014
Chlo
orine Measured
Chlorination Curve
Chlorine Added
36
Chloramination Curve
• Continue to add chlorine to the water
– After chlorine demand is exhausted, chlorine reacts
with ammonia to form monochloramine
HOCl + NH3  NH2Cl + H2O
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10/02/2014
Chloramination Curve
Chlo
orine Measured
Chloramination
I
5:1 Cl2:N Ratio
Chlorine Added
38
Weight Based Units
Atom
Atomic Weight Atom
Molecular Weight
Chlorine
35.5
Chlorine (Cl2)
71
Nitrogen
14
Ammonia (NH3)
17
H d
Hydrogen
1
M
Monochloramine
hl
i (NH2Cl)
51
1
Dichloramine (NHCl2)
85
Trichloramine (NHCl3)
129
How do we get to these desired ratios?
D i d from
Derived
f
balancing
b l
i
the
th chemical
h
i l reaction
ti
HOCl + NH3  NH2Cl + H2O
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10/02/2014
Weight Ratios for the Ideal World
1 mol Cl2
X
1 mol NH3
71 lb Cl2
X
1 mol Cl2
1 mol Cl2
X
1 mol NH3
71 lb Cl2
1 mol NH3
=
17 lb NH3
X
1 mol Cl2
1 mol NH3
1 mol N
71 lb Cl2
=
17 lb NH3
X
1 mol N
14 lb N
4.2 lb Cl2
1 lb NH3
=
71 lb Cl2
=
14 lb N
5.06 lb Cl2
1 lb N
1 molecule of Free Chlorine reacts with
1 molecule of Free Ammonia to form
1 molecule of Monochloramine
40
Chloramination Curve
Chlo
orine Measured
Chloramination
I
5:1 Cl2:N Ratio
Chlorine Added
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10/02/2014
Chloramination Curve
Chlo
orine Measured
Chloramination
I
5:1 Cl2:N Ratio
Chlorine Added
42
Chloramination Curve
• 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
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10/02/2014
Chloramination Curve
• 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
44
Chloramination Curve
• Continue to add chlorine to the water
– The point at which all dichloramine is converted to
g g
gas is the breakpoint.
p
nitrogen
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10/02/2014
Chloramination Curve
Chlo
orine Measured
Chloramination
I
5:1 Cl2:N Ratio
II
Breakpoint
9:1 Cl2:N Ratio
Chlorine Added
46
Chloramination Curve
Chlo
orine Measured
Chloramination
I
5:1 Cl2:N Ratio
II
Breakpoint
9:1 Cl2:N Ratio
Chlorine Added
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10/02/2014
Chloramination Curve
• 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 + OCl48
Chloramination Curve
Chlo
orine Measured
Chloramination
I
5:1 Cl2:N Ratio
Free Chlorination
II
III
Breakpoint
9:1 Cl2:N Ratio
Chlorine Added
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10/02/2014
Chloramination Curve
Chlo
orine Measured
Chloramination
I
Free Chlorination
II
5:1 Cl2:N Ratio
III
Breakpoint
9:1 Cl2:N Ratio
Chlorine Added
50
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
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10/02/2014
Chloramination Goals
• Real world operating conditions can influence the
process
–
–
–
–
–
pH
Temperature
Chlorine demand
Reaction time, competing reactions
Chloramine decay
52
Chloramination Species
• Curve we have been looking at is total chlorine
• Wh
Whatt other
th species
i are involved
i
l d iin
chloramination and what happens to their
concentrations?
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10/02/2014
Chloramination Species
Chlo
orine Measured
Chloramination
I
Free Chlorination
II
III
Total
Chlorine
Chlorine Added
54
Free Ammonia
• Free ammonia reacts with chlorine to form
monochloramine until ammonia has been
consumed
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10/02/2014
Chloramination Species
Chlo
orine Measured
Chloramination
Free Chlorination
I
II
III
Total
Chlorine
Free
Ammonia
Chlorine Added
56
Monochloramine
• Monochloramine is equivalent to total chlorine
until Section II where it reacts with chlorine to
form new compounds.
• No monochloramine remains at the breakpoint.
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10/02/2014
Chloramination Species
Chlo
orine Measured
Chloramination
Free Chlorination
I
Total
Chlorine
II
III
Monochloramine
Free
Ammonia
Chlorine Added
58
Free Chlorine
• Free chlorine does not exist until after the
breakpoint.
• After the breakpoint, all chlorine added to the
system exists as free chlorine.
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10/02/2014
Chloramination Species
Chlo
orine Measured
Chloramination
Free Chlorination
I
II
Total
Chlorine
Monochloramine
III
Free
Chlorine
Free
Ammonia
Chlorine Added
60
“Combined” Chlorine Test Problems
• Theory goes that
– Total Chlorine Test = Free Cl2 + Monochloramine +
Dichloramine
– Free Chlorine Test = Free Cl2
– Total Test – Free Test = “Combined Chlorine”
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10/02/2014
“Combined” Chlorine Test Problems
• Problems
– Can’t tell if you have the desired monochloramine
species
p
– Free Cl2 measurements in presence of high levels of
chloramines are inaccurate
– Chloramines “break through” and increase the Free Cl2
test value
• Use an analytical method that measures what
you are looking for:
– Monochloramine and free ammonia
62
CHLORAMINATION
TESTING
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10/02/2014
Chloramination Monitoring
• Monitor chloramines by measuring directly
• Monochlor-F method
• Chemical method specific for monochloramine
• Few interferences
• Optimized for chloramination monitoring
64
Chloramination Monitoring
• Monitor ammonia using:
– Ion selective electrode (ISE)
– Monochloramine and free ammonia test
• Colorimetric method – most Hach instruments either have it or
can be upgraded to run it
• A sequential test that first measures monochloramine, then
sample is chlorinated to measure increase in monochloramine
concentration
• Amount of free ammonia is calculated based on the increase
in monochloramine
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10/02/2014
Chloramination Monitoring
• Monitor chloramination process using:
– Total chlorine
– Free chlorine
• Monochloramine will give a false-positive result in a free
chlorine test
• Be aware of where free chlorine exists in chloramination (know
where you are on chloramination curve)
• Use FreeChlorF test in special cases
66
Chloramines
• Chloramination - Why so many tests?
• Combination of ammonia and monochloramine (and
(
maybe total chlorine) lets you know exactly where your
process is on the breakpoint curve
• Keeping process under control saves time and money
• Can also improve aesthetics and perceived quality of your
product
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10/02/2014
Where Am I When
Total Chlorine = 3mg/L?
Chlo
orine Measured
Chloramination
I
Free Chlorination
II
III
Chlorine Added
68
I Am Here!
Chlo
orine Measured
Chloramination
Free Chlorination
I
II
III
NH2Cl = tt-DPD
t-DPD
NH2Cl < t-
t-DPD > 0
f-NH3-N > 0
f-NH3-N = 0
NH2Cl = 0
f-NH3-N = 0
Chlorine Added
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10/02/2014
HANDS ON LAB TESTING
HANDS-ON
70
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10/02/2014
APPLYING THE CONCEPTS
72
Applying the Concepts
• What to measure
• Where
Wh
to
t measure
• What results are we targeting
• How to make changes
g based on the data
73
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10/02/2014
To run the process we need
• Measured Concentrations of:
– Free Chlorine
– Monochloramine
Total Chlorine
Free Ammonia
• Goal Target Levels of these same parameters
• Current feed rates of chemicals
• Molecular Weights and Formulas for Chemicals Added
• Concentration and specific gravity of each liquid
Chemicals Added
74
What to measure
• Free Chlorine
– Make sure we added the correct amount
– Determine how much ammonia needs to be added to form
hl
i
monochloramine
• Free Ammonia
– If we applied too much ammonia
– Determine how much Cl2 needs to be added to form
monochloramine
• Monochloramine
– to
t ensure our ratio
ti off Cl2 to
t NH3 was correctt
• Total Chlorine
– To see if other chloramines were formed
75
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10/02/2014
Where to measure
• Regulated Parameters
– At locations required by local regulators
– End of disinfection zone
– Point of Entry to distribution
• Process Control
– Upstream of the chemical injection points
– Down stream of the chemical injection points
76
Injection Points
Cl2
Cl2
NH3
Cl2
NH3
77
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10/02/2014
Free Chlorine
Cl2
Cl2
NH3
Cl2
NH3
78
Total Chlorine
Cl2
Cl2
NH3
Cl2
NH3
79
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10/02/2014
Monochloramine
Cl2
Cl2
NH3
Cl2
NH3
80
Free Ammonia
Cl2
Cl2
NH3
Cl2
NH3
81
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10/02/2014
What are our goals?
• Free Chlorine to meet CT requirements
• Free Chlorine concentration to meet target
Monochloramine level
• Add ammonia based on desired target ratio
• Maintain a small target residual typically 0.05 mg/l NH3
• Know where you are on the curve!
82
MAKING ADJUSTMENTS
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10/02/2014
Making Adjustments
Condition
Remedy
Note
Free Cl2 > NH2Cl Target
Reduce Cl2 dosage
Prior to NH3
NH2Cl too High
Reduce NH3 dose, then
Measure, adjust one at a time
NH3 too High
Increase Cl2 dosage OR
R d
Reduce
Cl2 dosage
d
Adjust only one parameter
Reduce NH3 dose
No Residual NH3
Increase NH3 dosage OR
Adjust only one parameter
Reduce Cl2 dose
Total Cl2 > NH2Cl
Reduce Cl2 dosage OR
You are in Section II
Increase NH3 dose
84
SPECIAL SITUATIONS
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10/02/2014
Special Situations
• Source Water with Natural Ammonia
–
–
–
–
Use the salicylate method or ISE for Ammonia measurement
Free ammonia method, Nessler method not recommended
Make sure measurements are made in new GW Chlorination systems
Preoxidation Cl2 sufficient to move to Section III
86
Special Situations
• Need to increase Chloramine Residual
– Know where you are on the curve
– Add in specified ratios and stay in Section I
• Reduce Free Ammonia Levels to avoid nitrification
– Measure free ammonia and add chlorine only, Section I
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10/02/2014
Blended Consecutive Systems
• Mix usually pushes Into Section II
• Strategy 1
– Push through Breakpoint to Section III
– Cl2-F with FreeChlorF Reagent
– Risk of additional DBP
• Strategy 2
–
–
–
–
Measure Cl2-F
M
F with
ith DPD
Convert Chlorinated Source to Chloraminated
Add ammonia at proper ratio
Blend produced waters
88
DETERMINING AMMONIUM
FEED RATE
89
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10/02/2014
Liquid Ammonium Sulfate Example
• Liquid Ammonium Sulfate (LAS)
– What is LAS?
• 38-40% aqueous solution of (NH4)2SO4
• Specific Gravity of 1.216 to 1.228 or 10.15 to 10.25 #/gallon
• Roughly 10% as Ammonia NH3
90
Liquid Ammonium Sulfate Example
So, a 40% LAS solution
weighs ~10 #/gallon and
each gallon contains 0
0.84
84 # N
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10/02/2014
Liquid Ammonium Sulfate Example
Coarse Control:
Expected Chlorine Feed pump rate at 4 #/hr.
q
for a 4.5:1 Ratio ((Chlorine :
How much LAS required
Nitrogen)?
92
Liquid Ammonium Sulfate Example
• Fine Control:
Frequent laboratory measurements
On-line analysis
• Measure, feedback, adjust and measure
again…
What change do I need to do
make with these readings?
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10/02/2014
Nitrification
• Ammonia is converted to Nitrate
– Ammonia to Nitrite by nitrosomonas
– Nitrite to Nitrate by nitrobacters
• Increasing risk
– warmer temperatures 25-30 C
– Longer detention times in distribution
• Adverse acute health impacts (blockage of 02 transport)
94
Nitrification
• What to watch for
–
–
–
–
–
–
–
Loss of residual disinfection
Increase in HPC (using R2A agar)
Lowering of pH
Decrease in alkalinity
Reduced dissolved oxygen
Increase in Nitrite
Increase in Nitrate
• What to do
– Increase flushing
– Periodic free chlorine “burn” *Remember Notifications
95
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10/02/2014
Summary
• Goal : Provide a more in-depth understanding of the
Disinfection Process using Chloramines
• Balance is Key: Experience proves that the
chloramination process can be extremely effective, but
only if the concentration of ammonia and chlorine in the
system remains in proper balance.
• Understand the Reactions: For optimal control of the
chloramination process, understanding of the reactions
taking place and measurement of the proper parameters
can simplify operation and ensure proper disinfection
96
Take Away Messages
• Monochloramine can help reduce DBPs
• Proper measurement is the key to effective control
• Know through analysis where you are on the Chlorine
Breakthrough Curve
• Target a Cl2 to N ratio of 3-5:1 to avoid dichloramine
formation
• Minimize unreacted ammonia – free ammonia >than but
close to 0
• When making process changes
changes, change only one variable
at a time
97
48
10/02/2014
Questions ?
Chris Griffin
Hach Company
p y
804-513-6731
[email protected]
98
49