Comprehensive Overview of Water Disinfection and Chlorination Basics
Disinfection Overview
Workshop developed by RCAP/AWWA and funded by the USEPA
Learning Objectives
•
Be able to discuss the purpose and types
of disinfection
•
Be able to discuss the basics of
chlorination and chloramination
Topics to be Covered
•
Why is disinfection needed?
•
Types of disinfectants
•
Chlorination basics
•
Chloramination basics
•
Unintended consequences of
chloramination (nitrification)
Why do water systems disinfect?
•
To kill pathogens in water (from source or distribution
system contamination)
•
Residuals prevent biofilm buildup in the distribution
system
•
Adds an additional barrier to protect the public from
waterborne disease
Why do we need multiple barriers?
•
A
n
y
b
a
r
r
i
e
r
c
a
n
f
a
i
l
•
Not all microbes are easily filtered (viruses)
•
Not all microbes are disinfected by chlorine (Crypto)
•
The cumulative effect of multiple barriers greatly reduces the
likelihood of pathogens reaching the consumer
What are the types of disinfection?
•
Chlorine
•
Chloramines
•
Chlorine dioxide
•
Ozone
•
UV (Ultraviolet disinfection)
Which disinfectant(s) provide
protection in the distribution system?
Which disinfectants provide protection
in the distribution system?
•
Chlorine
•
Chloramines
Disinfectants that do not provide distribution
system residuals (
and not covered in this
training
)
:
•
Chlorine dioxide
•
Ozone
•
UV (Ultraviolet disinfection)
Chlorination
•
Chlorine is the most common disinfectant used
in the U.S.
•
Common forms are:
–
Chlorine gas
•
Cl
2(g)
+ H
2
O → HCl + HOCl + Cl
-
•
HOCl ←→ H
+
+ OCl
-
–
Bleach (NaOCl)
–
Chlorine powder (High Test Hypochlorite (HTH),
Ca(OCl)
2
)
Impacts of pH on Chlorine
Disinfection
•
pH impacts the form of
Chlorine
•
Chlorine is most
effective between pH
5.5 – 7.5
hypochlorous
water H
2
0
acid HOCl
pH dependent
Chlorination
Typical surface water chlorination
Pre-Sedimentation
Flocculation &
Sedimentation
Primary
Chlorination
Pre-chlorination
Booster
Chlorination
Chloramination
(Combined Chlorine)
•
React free chlorine with ammonia to form chloramines, a weaker
disinfectant
•
H
O
C
l
+
N
H
3
→
N
H
2
C
l
+
H
2
O
(
m
o
n
o
c
h
l
o
r
a
m
i
n
e
)
G
O
O
D
•
NH
2
Cl + HOCl → NHCl
2
+ H
2
O (dichloramine)
•
N
H
C
l
2
+
H
O
C
l
→
N
C
l
3
+
H
2
O
(
t
r
i
c
h
l
o
r
a
m
i
n
e
)
B
A
D
•
Typically, monochloramine is the dominant species and is best
disinfectant
p
l
u
s
Hypochlorous Acid
Ammonia
monochloramine
(free chlorine)
Chloramination
Chloramination
Chloramination
Chlorination
Typical groundwater chlorination
Chlorination with no free chlorine
Typical groundwater chlorination
Booster Disinfection
•
Chlorine decays in the distribution system
•
Dosing chlorine in the distribution system (booster
chlorination) maybe be required to maintain an
acceptable chlorine residual
•
Booster chlorination may pick up any free
ammonia to produce chloramine
•
Booster chloramination may be undertaken
Free, Combined and Total Chlorine
•
Which do you use?
What are the different types of
chlorine?
•
Free chlorine – residual comprised of hypochlorite
and hypochlorous acid
–
HOCL and OCL
-
•
Combined chlorine – chlorine combined with other
water quality constituents
–
Chloramines
•
Total chlorine – sum of free and combined chlorine
Free Chlorine + Combined Chlorine = Total Chlorine
Free and Combined Chlorine
•
Free chlorine
–
Stronger oxidant
–
Less stable, faster decay
•
Combined chlorine (
mostly chloramines
)
–
Weaker oxidants
–
More stable, slower decay
–
Do you chloraminate?
Chloramines
•
Produce very little TTHM and HAA5
–
Many utilities have switched to chloramination to
comply with the Stage 2 DBPR
•
Ammonia may cause biological growth or
nitrification in the distribution system
Interaction between Chlorine and
other Water Components
Chlorination Dose
•
How to ensure the right dosage is applied?
–
Measure Cl
2
residual in the distribution
system
–
Make sure metering pump is working
properly
–
Check Cl
2
stock strength regularly
Hypochlorite injector clogged with calcium
Chlorination Dose
•
Chlorine decays over time in the distribution
system
–
Inadequate chlorine residual may enable
pathogens to survive or multiply
–
It is important to maintain an acceptable
residual at all locations at all times
Chlorine Dose Calculation
•
What is the initial Cl
2
dose if:
–
Stock chlorine solution is 10%
–
Flow rate is 200 gpm
–
Chlorine feed rate is 1.2 gph
•
Chlorine concentration
–
1% NaOCl = 10,000 ppm = 10,000 mg/L
–
10% NaOCl = 100,000 ppm = 100,000 mg/L
–
1 gallon = 3.78 liters
Chlorine Dose Calculation Solution
•
What is the initial Cl
2
dose if:
–
Stock chlorine solution is 10%
–
Flow rate is 200 gpm
–
Chlorine feed rate is 1.2 gph
•
Chlorine concentration
–
1% NaOCl = 10,000 ppm = 10,000 mg/L
–
10% NaOCl = 100,000 ppm = 100,000 mg/L
–
1 gallon = 3.78 liters
•
Chlorine feed rate: 1.2 gph X 100,000 mg/L =
(1.2 X 3.78)/60 X 100,000 mg/min = 7560 mg/min
•
Chlorine concentration: chlorine feed rate / flow =
7560 / (200 X 3.78) mg/L = 10 mg/L
Disinfection Monitoring – Point of
Entry
Monitoring Chlorine Concentration
– Point of Entry
•
Residual disinfectant concentration
cannot be less that 0.2 mg/L entering
the distribution system for
more than 4 hours
•
Larger systems must be monitored
continuously
–
Lowest value must be recorded each day
•
If the continuous monitoring equipment
fails:
–
Grab sampling every 4 hours, but for no more
than 5 working days
SHOW OF HANDS:
•
How many have continuous
analyzers?
•
How often are they calibrated?
–
weekly
–
monthly
–
don’t know
Monitoring Chlorine Concentration
– Point of Entry
Monitoring Chlorine Concentration
in the Distribution System
•
Cannot be undetectable in more than 5%
of the samples collected from the
distribution system
•
Should be taken from the same location
and at the same time as Total Coliform
sample
Nitrification
N
i
t
r
i
f
y
i
n
g
b
a
c
t
e
r
i
a
f
e
e
d
o
n
a
m
m
o
n
i
a
…
producing Nitrites…
which exert a chlorine demand…
which decreases the residual…
which allows microbes to flourish…
to produce more nitrites…
w
h
i
c
h
c
o
n
t
i
n
u
e
s
t
h
e
s
p
i
r
a
l
…
u
n
t
i
l
y
o
u
r
r
e
s
i
d
u
a
l
i
s
g
o
n
e
!
a
k
a
…
“
f
e
e
d
i
n
g
t
h
e
b
e
a
s
t
”
Nitrification
Nitrification rates affected by:
•
pH
•
Temperature
•
Dissolved oxygen concentration
•
Free ammonia
•
Water age
Controlling Nitrification
•
Keep the residual high during summer (4 mg/L not
uncommon)
•
T
a
n
k
c
y
c
l
i
n
g
(
r
o
u
t
i
n
e
a
n
d
d
e
e
p
…
b
u
t
c
a
n
l
e
a
d
t
o
f
e
e
d
i
n
g
t
h
e
b
e
a
s
t
)
•
Targeted DS Flushing
−
At dead ends
−
Throughout DS (unidirectional)
−
At points of low chlorine
−
Associated with tank cycling
Remediating Nitrification
•
Complete DS Flushing
•
Tank Draining (dropping the tank)
•
Booster chlorination
•
Free chlorination (DS burn)
•
Source water break point chlorination (if
you are not already)
•
Chlorite addition (chlorite is regulated)
Can nitrification be experienced in
free chlorine systems?
•
Some free ammonia may exist in natural
waters
•
What is your reaction when you get a
complaint on a strong chlorine taste and
odor?
•
Trichloramines have the strongest chlorine
odor and you actually need to increase the
chlorine dose to achieve breakpoint/eliminate
“chlorine” odor
Chloramination Recommendations
S
y
s
t
e
m
s
t
h
a
t
c
h
l
o
r
a
m
i
n
a
t
e
s
h
o
u
l
d
h
a
v
e
a
N
i
t
r
i
f
i
c
a
t
i
o
n
C
o
n
t
r
o
l
P
l
a
n
t
h
a
t
i
n
c
l
u
d
e
s
:
•
The chlorine to ammonia ratio target
•
Historical data graphed for analysis
•
Operational targets:
•
Procedures for chemical adjustment, monitoring and review
of data
•
The monitoring equipment/test kits and/or lab procedures that
are approved/acceptable by USEPA/local regulatory agency
Questions
•
Does your system apply free chlorine only?
•
Where is it applied?
•
What is applied dose?
•
What is measured residual at POE?
•
What is measured residual in the distribution
system?
•
Does your system booster chlorinate?
Note that while we will mention the different types of disinfection methods available, this module is focused on disinfection by free chlorine and combined chlorine (chloramine) only.
Developed by American Water Works Association with funds from the U.S. Environmental Protection Agency, Published 2015
This workshop explores the importance and various methods of water disinfection, focusing on chlorination basics, chloramines, disinfection types, and the impacts of pH on chlorine disinfection. Learn about the necessity of disinfection in water systems, different disinfectants used, and the need for multiple barriers to safeguard against waterborne pathogens. Discover why chlorine is a commonly used disinfectant, its forms, and its role in preventing biofilm buildup and protecting public health.
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Presentation Transcript
Disinfection Overview Workshop developed by RCAP/AWWA and funded by the USEPA
Learning Objectives Be able to discuss the purpose and types of disinfection Be able to discuss the basics of chlorination and chloramination
Topics to be Covered Why is disinfection needed? Types of disinfectants Chlorination basics Chloramination basics Unintended consequences of chloramination (nitrification)
Why do water systems disinfect? To kill pathogens in water (from source or distribution system contamination) Residuals prevent biofilm buildup in the distribution system Adds an additional barrier to protect the public from waterborne disease Viruses Bacteria (e.g. E. coli) Protozoa
Why do we need multiple barriers? Any barrier can fail Not all microbes are easily filtered (viruses) Not all microbes are disinfected by chlorine (Crypto) The cumulative effect of multiple barriers greatly reduces the likelihood of pathogens reaching the consumer Viruses Bacteria (e.g. E. coli) Protozoa
What are the types of disinfection? Chlorine Chloramines Chlorine dioxide Ozone UV (Ultraviolet disinfection) Which disinfectant(s) provide protection in the distribution system?
Which disinfectants provide protection in the distribution system? Chlorine Chloramines Disinfectants that do not provide distribution system residuals (and not covered in this training): Chlorine dioxide Ozone UV (Ultraviolet disinfection)
Chlorination Chlorine is the most common disinfectant used in the U.S. Common forms are: Chlorine gas Cl2(g) + H2O HCl + HOCl + Cl- HOCl H+ + OCl- Bleach (NaOCl) Chlorine powder (High Test Hypochlorite (HTH), Ca(OCl)2)
Impacts of pH on Chlorine Disinfection pH impacts the form of Chlorine Chlorine is most effective between pH 5.5 7.5 water H20 hypochlorous acid HOCl O O H Cl H H pH dependent
Chlorination Typical surface water chlorination Primary Chlorination Pre-chlorination Secondary Chlorination Booster Chlorination Pre-Sedimentation Flocculation & Sedimentation Filtration Clear well
Chloramination (Combined Chlorine) React free chlorine with ammonia to form chloramines, a weaker disinfectant HOCl + NH3 NH2Cl + H2O (monochloramine) GOOD NH2Cl + HOCl NHCl2 + H2O (dichloramine) NHCl2+ HOCl NCl3 + H2O (trichloramine) BAD Typically, monochloramine is the dominant species and is best disinfectant N O Cl N H H plus Cl H H H H monochloramine Hypochlorous Acid (free chlorine) Ammonia
Chloramination ammonia Free chlorine CT
Chloramination Primary Chlorination ammonia Free chlorine CT if no pre-chlorine
Chloramination ammonia
Chlorination Typical groundwater chlorination Primary Chlorination Booster Chlorination Secondary Chlorination Storage Tank Distribution System Groundwater Well
Chlorination with no free chlorine Typical groundwater chlorination Primary Chlorination ammonia/phosphate addition Storage Tank Distribution System Groundwater Well
Booster Disinfection Chlorine decays in the distribution system Dosing chlorine in the distribution system (booster chlorination) maybe be required to maintain an acceptable chlorine residual Booster chlorination may pick up any free ammonia to produce chloramine Booster chloramination may be undertaken
Free, Combined and Total Chlorine Which do you use?
What are the different types of chlorine? Free chlorine residual comprised of hypochlorite and hypochlorous acid HOCL and OCL- Combined chlorine chlorine combined with other water quality constituents Chloramines Total chlorine sum of free and combined chlorine Free Chlorine + Combined Chlorine = Total Chlorine
Free and Combined Chlorine Free chlorine Stronger oxidant Less stable, faster decay Combined chlorine (mostly chloramines) Weaker oxidants More stable, slower decay Do you chloraminate?
Chloramines Produce very little TTHM and HAA5 Many utilities have switched to chloramination to comply with the Stage 2 DBPR Ammonia may cause biological growth or nitrification in the distribution system
Interaction between Chlorine and other Water Components
Chlorination Dose How to ensure the right dosage is applied? Measure Cl2 residual in the distribution system Make sure metering pump is working properly Check Cl2 stock strength regularly Hypochlorite injector clogged with calcium
Chlorination Dose Chlorine decays over time in the distribution system Inadequate chlorine residual may enable pathogens to survive or multiply It is important to maintain an acceptable residual at all locations at all times
Chlorine Dose Calculation What is the initial Cl2 dose if: Stock chlorine solution is 10% Flow rate is 200 gpm Chlorine feed rate is 1.2 gph Chlorine concentration 1% NaOCl = 10,000 ppm = 10,000 mg/L 10% NaOCl = 100,000 ppm = 100,000 mg/L 1 gallon = 3.78 liters
Chlorine Dose Calculation Solution What is the initial Cl2 dose if: Stock chlorine solution is 10% Flow rate is 200 gpm Chlorine feed rate is 1.2 gph Chlorine concentration 1% NaOCl = 10,000 ppm = 10,000 mg/L 10% NaOCl = 100,000 ppm = 100,000 mg/L 1 gallon = 3.78 liters Chlorine feed rate: 1.2 gph X 100,000 mg/L = (1.2 X 3.78)/60 X 100,000 mg/min = 7560 mg/min Chlorine concentration: chlorine feed rate / flow = 7560 / (200 X 3.78) mg/L = 10 mg/L
Disinfection Monitoring Point of Entry Point of Entry Storage Tank Distribution System Groundwater Well
Monitoring Chlorine Concentration Point of Entry Residual disinfectant concentration cannot be less that 0.2 mg/L entering the distribution system for more than 4 hours Larger systems must be monitored continuously Lowest value must be recorded each day If the continuous monitoring equipment fails: Grab sampling every 4 hours, but for no more than 5 working days
Monitoring Chlorine Concentration Point of Entry SHOW OF HANDS: How many have continuous analyzers? How often are they calibrated? weekly monthly don t know
Monitoring Chlorine Concentration in the Distribution System Cannot be undetectable in more than 5% of the samples collected from the distribution system Should be taken from the same location and at the same time as Total Coliform sample
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
Nitrification Nitrification rates affected by: pH Temperature Dissolved oxygen concentration Free ammonia Water age
Controlling Nitrification Keep the residual high during summer (4 mg/L not uncommon) Tank cycling (routine and deep but can lead to feeding the beast) Targeted DS Flushing At dead ends Throughout DS (unidirectional) At points of low chlorine Associated with tank cycling
Remediating Nitrification Complete DS Flushing Tank Draining (dropping the tank) Booster chlorination Free chlorination (DS burn) Source water break point chlorination (if you are not already) Chlorite addition (chlorite is regulated)
Can nitrification be experienced in free chlorine systems? Some free ammonia may exist in natural waters What is your reaction when you get a complaint on a strong chlorine taste and odor? Trichloramines have the strongest chlorine odor and you actually need to increase the chlorine dose to achieve breakpoint/eliminate chlorine odor
Chloramination Recommendations Systems that chloraminate should have a Nitrification Control Plan that includes: The chlorine to ammonia ratio target Historical data graphed for analysis Operational targets: Procedures for chemical adjustment, monitoring and review of data The monitoring equipment/test kits and/or lab procedures that are approved/acceptable by USEPA/local regulatory agency
Questions Does your system apply free chlorine only? Where is it applied? What is applied dose? What is measured residual at POE? What is measured residual in the distribution system? Does your system booster chlorinate?
