Transcript Monitoring and Assessing Water Quality

Chlorination in Waterworks
Operation
Waterworks Operations I
WQT 111
Chlorination
http://www.c3.org/chlorine_knowledge_center/history.html
http://www.wrb.state.ri.us/programs/eo/historydrinkingwater.htm
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
Week Objectives
Reading assignment: Water Treatment , Chapter 7: Disinfection
1. Comprehend “the basics” of chlorine chemistry
2. Understand the advantages and disadvantages of
chlorine
3. Understand the history of chlorine via a timeline
4. Understand Breakpoint Chlorination Curve
5. Calculate C•T values
Key Words
Chlorine Residual- Measurable chlorine remaining
after the demand is satisfied.
Chlorine Demand- The amount of chlorine destroyed
by reaction with Fe, Mn, turbidity, organics, and
microorganisms in the water.
Free Chlorine Residual- point past breakpoint where
HOCl (hypochlorous acid) and OCL- (hypochlorite ion) form.
25 times more powerful than combined chlorine for
disinfection
Combined residual chlorine: chlorine combined with organics
or ammonia.
• NH2Cl (monochloramine) and
• NH(Cl)2 (dichloramine)
• N(Cl)3 (nitrogen trichloride)
Key Words
Breakpoint chlorination: The point at which near
complete oxidation of nitrogen compounds are
reached . Any point beyond breakpoint is mostly
free chlorine (HOCL and OCL-)
C•T (concentration and contact time): Effectiveness
of chlorination is dependant on chlorine
concentration and contact time.
Sterilization: The destruction of all living things in a
sample
Disinfection: The removal or inactivation of disease
causing (pathogenic) organisms
Chlorine Demand= Chlorine Dose- Chlorine Residual
The destruction of the larger
portion of microorganisms with
the probability that all pathogens
are killed is called
79%
Digestion
Disinfection
Dilution
Sterilization
Disposal
21%
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D
1.
2.
3.
4.
5.
Proper disinfection kills all
organisms?
1. True
2. False
91%
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Fa
Tr
ue
9%
Chlorine applied minus ____
equals chlorine residual
Chlorine dose
Chlorine demand
Combined chlorine
Free chlorine
Total chlorine
88%
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To
6%
C
1.
2.
3.
4.
5.
CL2 Demand= Cl2 Dose- Cl2 Residual?
93%
Fa
ls
e
7%
Tr
ue
1. True
2. False
A low chlorine dose w/ longer the
contact time can have the same
disinfecting power as a high
chlorine dose with a short detention
time?
100%
1. True
2. False
ls
e
Fa
Tr
ue
0%
The amount of chlorine destroyed by
reaction with Fe, Mn, turbidity,
organics, and microorganisms in the
water?
1. Free Chlorine Residual
2. Chlorine Demand
3. Chlorine Residual
83%
al
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6%
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11%
Measurable chlorine
remaining after the demand is
satisfied.
100%
1. Chlorine Demand
2. Chlorine Residual
id
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HOCL?
1. Hypochlorous acid
2. Hypochlorite ion
3. Dichloramine
89%
11%
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HOCL?
1. Common at pH < 6
2. Most powerful/effective
disinfectant
3. All of the above
95%
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NH2Cl
1. Monochloramine
2. Combined Residual Chlorine
3. Not as effective as a disinfectant as
hypochlorus acid
4. All of the above
89%
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6%
Sterilization only removes
pathogenic organism from a
water sample?
1. True
2. False
100%
ls
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Fa
Tr
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0%
Chlorine Advantages
1. Chlorine provides a strong residual in the
distribution system.
2. Chlorine can be easily converted to chloramines
which also provide a strong residual and do not
produce by-products.
3. Chlorine is easy to apply. Can use it in liquid,
solid, or gas form
4. Chlorine is a relatively inexpensive disinfecting
agent.
5. Chlorine is effective at low concentrations.
Chlorine Disadvantages
1. When chlorine reacts with organic material its'
concentration is reduced and
trihalomethanes(THM's), haloacetic acids (HAA5),
chlorite (when chlorine dioxide is used) and bromate
(when ozone is used) are disinfection-by-products
(DBP's). These compounds are carcinogenic.
2. Chlorine provides poor Cryptosporidium and Giardia
control.
3. Effectiveness varies depending on turbidity,
[ammonia], pH, etc.
4. Chlorine is a dangerous and potentially fatal
chemical if used improperly
According to the Stage 1
Disinfectant/Disinfection
Byproducts Rule which of the
following are considered
haloacetic acids (HAA5) DPBs
disinfectant byproducts?
92%
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Monochloroacetic acid
Dichloroacetic acid
Monobromoacetic acid
All of the above
M
1.
2.
3.
4.
An advantage of chlorine is that
it can be a liquid, solid, or a
gas?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
Chlorine can completely remove
Giardia and Cryptosporidium
from water?
1. True
2. False
100%
ls
e
Fa
Tr
ue
0%
Chlorine Disinfection Timeline
500 BC- Boiling of water recommended by Hippocrates
1879- Chlorine was applied as a disinfectant for the first time
(England).
1893-First time chlorine applied on a plant scale basis
(Hamburg, Germany).
1903- First time chlorine gas was used as a disinfectant in
drinking water (Middlekerke, Belgium).
1908- The first full scale chlorine installation at a drinking
water plant in the United States was initiated in this year.
(Bubbly Creek Filter Plant in Chicago)
Chlorine Chemistry Timeline
1744- S.W. Scheele, a Swedish chemist, discovers chlorine.
1810-Chlorine was identified as a chemical element by Davey
and called Chlorine (chlorous) due to its pale yellow/green
color
1909 Liquid chlorine bleach becomes available after the
Niagara Starch Co. in NY develops a production method.
1914-Wallace and Tiernan develop chlorine gas feed
equipment
1914 CR Cox describes experiments with chlorine that are
called “double chlorination” (Discovered breakpoint)
1928 The Olin Corporation begins production of High Test
Hypochlorite dubbed “HTH”
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html#History
Chlorination Methods Timeline
1939- A.E. Griffin explains “Breakpoint Chlorination”
1942-Henry Marks invents the amperometric chlorine residual
analyzer.
1973-JJ Rook discovers chloroform (trtihalomethane) in
drinking water in New Orleans and Corvallis.
1974- the SDWA is passed into law by congress.
1986 -The Surface Water Treatment Rule requires disinfection
of all surface water and groundwater under the influence of
surface water (GWUISW)
1986- USEPA approves four methods of drinking water
disinfection. Disinfection C•T requirements for each
disinfectant are established to insure inactivation of
Giardia and viruses
-Chlorination, Chloramines, Ozone, UV light
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html#History
2003- USEPA approves UV disinfection
for Crypto
SDWA Amendments
December 16,1998 promulgated
Disinfection Byproduct Rule (DBPR):
Stage 1 DBPR **Stage 2 in the works!**
• MCLs for trihalomethanes, haloacetic acids, bromate, and
chlorite.
• Maximum residual disinfectant level goals (MRDLs) were also
finalized for chlorine, chloramines, and chlorine dioxide.
“Community water systems and non-transient non-community systems,
including those serving fewer than 10,000 people, that add a
disinfectant to the drinking water during any part of the treatment
process.”
MRDLGs for chlorine (4 mg/L), chloramines (4 mg/L), and chlorine dioxide
(0.8 mg/L);
• MCLs for total trihalomethanes - a sum of the four listed above (0.080
mg/L), haloacetic acids (HAA5) (0.060 mg/L)- a sum of the two listed
above plus monochloroacetic acid and mono- and dibromoacetic
acids), and two inorganic disinfection byproducts (chlorite (1.0 mg/L))
and bromate (0.010 mg/L));
SDWA Amendments
• May 1996- Information Collection Rule (ICR), occurrence data
for DBPs and precursors, microbials, water quality parameters,
and treatment plant parameters.
Used to develop the Stage 2 DBPR and the Long Term 2
Enhanced Surface Water Treatment Rule (LT2ESWTR).
Interim Enhanced Surface Water Treatment Rule
-Applies to systems serving 10,000 or more people
January 2002
Long Term 1 Enhanced Surface Water Treatment Rule
-strengthen microbial controls for small systems
(i.e., those systems serving fewer than 10,000
people.)
SDWA Amendments
January 5, 2006
Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR).
All public water systems with surface water or groundwater
under the influence of surface water.
LT2 rule reduce illness linked with the contaminant
Cryptosporidium and other disease-causing
microorganisms in drinking water. Targets Cryptosporidium
treatment requirements to higher risk systems.
•Targeting additional Cryptosporidium treatment requirements
to higher risk systems
•Requiring provisions to reduce risks from uncovered finished
water storage facilities
•Providing provisions to ensure that systems maintain
microbial protection as they take steps to reduce the
formation of disinfection byproduct
Chlorine was first used as a
disinfectant in Europe in the late
1800s?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
Ozone, UV light, Chlorination,
and Chloramines are 4 EPA
approved disinfection methods?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
Chlorine (Cl2)
• Widely distributed element
• Most important use is bleach
• Toxic, noncombustible, yellow-green gas with a
pungent, irritating odor and strong oxidizing
effects
• 2.5 times as dense as air!
• Slightly soluble in water
– Combines with water to form hypochlorous acid
(HOCl) and hydrochloric acid (HCl)
• Highly corrosive causes injury when the gas
reacts with moisture in the body
Chlorine - Toxicity
• Major route of toxicity is inhalation
• Solutions that generate chlorine can
be highly corrosive to skin or GI tract
• Strong oxidizing capability
– Produce major tissue damage
Chlorine - Toxicity
• Hypochlorous acid
– Penetrates cells and react with
cytoplasmic proteins, enzymes
– Form N-chloro derivatives that
destroy cell structure
– Can alter DNA replication of viruses
• Estimated lowest lethal concentration
– 30-min exposure is 430 ppm -- 1000
ppm
– Fatal within minutes
Chlorine is a toxic, corrosive,
gas?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
Which of the following is a
correct set of characteristics for
chlorine as used in disinfection?
4%
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3.
96%
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2.
Chlorine gas is colorless,
flammable, and heavier than air
Chlorine gas is colorless,
flammable, and lighter than air
Chlorine gas is greenish-yellow
(amber) in color, flammable,
and lighter than air
Chlorine gas in greenish-yellow
(amber) in color, toxic, lighter
than air, and noncorrosive
Chlorine gas is toxic, corrosive,
and heavier than air
C
1.
Protective Equipment
• Variety of rubber and plastic materials resist
chlorine
• Wear protective clothing appropriate to the type
and degree of contamination
• Use air-purifying or supplied-air respiratory
equipment
• Chlorine-resistant plastic sheeting and disposable
bags useful in preventing spread of contamination
Protective Equipment
Chlorine Chemistry
• Chlorine Atom:
Atomic Number 17
Atomic Weight 35.45 g
– Molecular Chlorine: Cl2
• Yellow-green gas (above 100 ppm)
• Chemical Classification
-"Oxidizer“, "Reactive“
********Two SMCL's apply to chlorine: 4 mg/l for Cl2, and
250mg/l for Cl-**
New MCL under consideration
Chlorine Chemistry Properties
Dry liquid: 100% gas
• Powder: Calcium Hypochlorite- 30, 65, 70%
chlorine
• Liquid: Sodium Hypochlorite: 5-15% chlorine
Density = 2.5 times as heavy as air, Irritant
• Boiling point -29.9 oF
• Freezing point -149.76 oF
• 1 part of liquid will produce 450 parts of gas
Maximum solubility: 1% at 49.2 oF
• Slightly soluble in water
• Temperatures below 49.2 will result in chlorine ice
• Insoluble in water at 212oF.
Where should sodium
hypochlorite (liquid bleach) be
stored?
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1. Away from flammable
objects, as it is a fire hazard
2. Away from equipment that
is susceptible to corrosion
3. closed containers at room
temperature for no longer
than 6 months
4. Near the chemical feed
pump day tank, to lessen
operator handling risks
Chlorine as a powder can have
purities of 30, 65, and 70%?
89%
Fa
ls
e
11%
Tr
ue
1. True
2. False
Sodium hypochlorite is manufactured by
the reaction of gaseous or liquid chlorine
with a solution of _________ _________
to produce a liquid containing NaOCl.
Sodium hydroxide
Potassium hydroxide
Potassium bisulfite
Sodium azide
86%
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1.
2.
3.
4.
Which form of hypochlorite is
the most dangerous to handle?
Sodium
Fluoride
Calcium
Chlorine
36%
27%
23%
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1.
2.
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4.
Chlorine gas is _____ times
heavier than air
96%
2.5
2.0
3.5
1.5
0%
1.
5
0%
3.
5
2.
4%
2.
5
1.
2.
3.
4.
Chlorine Chemistry
When Cl combines with water it produces
hypochlorous acid (HOCl) and hydrochloric acid
(HCl).
Cl2 + H2O
HOCl + HCl
hypochlorous acid and hypochlorite (OCL-) ion vary with pH.
Both HOCl and OCl are good disinfecting agents, but unionized hypochlorous acid (HOCl) is 100 times more effective
than hypochlorite (OCl-)
HOCL is stable below pH 6
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
Hypochlorous acid is the most
powerful disinfectant associated
with chlorine?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
pH Impact on Free Chlorine
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
What compound is first formed
when chlorine is applied to
water?
Hypochlorous acid
Hydrochloric acid
Chloramines
Free chlorine ions
75%
17%
Fr
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...
4%
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1.
2.
3.
4.
Chlorine will destroy bacteria
most rapidly at what pH?
100%
7.5
8.5
9.5
10.5
.5
0%
10
0%
9.
5
8.
5
0%
7.
5
1.
2.
3.
4.
Chlorine Chemistry in Water
1. Start with chlorine gas Cl2 + H2O
HOCl + HCl
2. If the pH of the water is greater than 8, the hypochlorus
acid (HOCl-) will dissociate (break) to yield hypochlorite
ion.
HOCl
H+ + OCl–
@pH>8
3. pH is less than 7, HOCl will not dissociate.
HOCl
HOCl
@pH<7
Free residual hypochlorous acid (HOCl) is more
1000 times more effective than combined residual
monochloramine
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
Which of the following is true
about chlorine chemistry?
1. pH < 7 favors
hypochlorous acid
2. pH >8 hypochlorite ions
form which can still
disinfectant
3. HOCL is 100 times more
powerful then OCL4. All of the above
100%
.
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0% 0% 0%
HOCL is 1,000 times more
powerful then monochloramine?
94%
Fa
ls
e
6%
Tr
ue
1. True
2. False
Basic Chlorine Compounds
Chlorine Demand: chlorine reacted with
– Clay, silt, iron, manganese, bacteria
Combined Chlorine Residuals
Chloramines: chlorine reacted with
– Inorganic ammonia compounds (NH3)
– Organic nitrogen proteins (amino acids)
– Less DBP
– Weak against virus and protozoa
Chlorine demand is satisfied at
the point when
96%
4%
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1. The reaction of chlorine
with organic and
inorganic materials
stops
2. Free chlorine residuals
reach 2.5 mg/L
3. An odor of chlorine is
present
4. Chlorine reaches the
last tap
Cl:NH3 and pH Impact in Water
1. If ammonia (NH3) is present in water, the
hypochlorus acid (HOCL) will react to form one
kind of chloramine depending on the pH,
temperature, and reaction time.
2. Monochloramine and dichloramine are formed at pH 4.5 8.5
3. Monochloramine is most common @pH>7.5; Cl2:NH3 <5:1
4. pH 4-5-7.5, Cl:NH3 > 5:1 -Monochloramine converts to
dichloramines
5. pH < 4.5, Cl2:NH3 ~15:1 -Trichloramine which produces a
very foul odor.
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
Chlorine-Ammonia (chloramines)
Chlorine- Ammonia reactions are governed by:
1.
2.
3.
4.
5.
Rates of formation of mono and dichloramine.
pH
Temperature
Time
Cl:NH3 ratio
Fact: High Cl:NH3 ratio, low temp & pH favor dichloramine
Combined Available Chlorine- chlorine existing in the water in
chemical combination with ammonia-nitrogen or organic
nitrogen
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
Chloramines in Water
Chloramines
3. pH 4.5-8.5; pH 8.0-8.5
Monochloramine: NH3 + HOCl
NH2Cl + H2O
2. pH 4.5-8.5; pH 4.5-8.0
Dichloramine: NH2Cl + 2HOCl
NHCl2 + 2H2O
4. pH <4.5
Trichloramine: NHCl2 + 3HOCl
NHCl3 + 3H2O
•Chloramines are an effective disinfectant against bacteria
but not against viruses.
•Add more chlorine to the wastewater to prevent the
formation of chloramines and form stronger disinfectants.
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
Add the Extra Free Chlorine
(HOCL)
5. Additional free chlorine (HOCL or OCL-) reacts with
chloramine to produce hydrogen ion, water , and nitrogen gas
which will come out of solution.
In the case of the monochloramine, the following reaction
occurs:
2NH2Cl + HOCl
N2 + 6HCl + H2O
Added free chlorine reduces the concentration of chloramines
in the disinfection process. Instead the chlorine that is added
is allowed to form the stronger disinfectant, hypochlorus acid.
http://ewr.cee.vt.edu/environmental/teach/wtprimer/chlorine/chlorine.html
If abundant (15 times) Cl is
around and the pH < 4.5
Trichloramine is the most likely
chloramine to form?
90%
Fa
ls
e
10%
Tr
ue
1. True
2. False
Which of the following impact
chloramine disinfection?
pH
Temperature
Time
All of the above
100%
m
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e
0%
ft
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ab
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0%
ra
tu
re
0%
pH
1.
2.
3.
4.
Ammonium nitrogen and
chlorine
Taste and Odor Problems
• Free (HOCL)
20 mg/L
• Monochloramine
5 mg/L
• Dichloramine
.8 mg/L
• Trichloramine
.02 mg/L
Chlorine Chemistry Summary
Cl2 + H2O
Chlorine
HCl
+
Hydrochloric
HOCl
Hypochlorous
Ca(OCl)2 (aqueous) Ca2+ +2 OClCalcium Hypochlorite Hypochlorite
NaOCl2 (aqueous)
Na+ + OClSodium Hypochlorite
Hypochlorite
HOCl
Hypochlorous
HOCl +
Hypochlorous
H+ + OClHypochlorite
NH3
Ammonia
NH2Cl + H2O
Chloramine
Chlorine Residual Analysis
• Starch Iodide Titration: common in wastewater
• Amperometric Titration: common in wastewater
with cloudy or turbidity problems
• DPD colorometric- common in water and
wastewater. Measures free residual or combined
residual.
Chlorine residual may be
determined using the reagent:
100%
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So
1. Diethyl-p-phenylene
diamine
2. Ethylene diamine
tetraacetic acid
3. Polychlorinated
biphenyls
4. Sodium thiosulfate
Which of the following methods
is not used to determine chlorine
residual?
70%
Photometric
Iodometric
Titrimetric
Amperometric
25%
5%
A
m
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0%
Ph
1.
2.
3.
4.
A chlorine demand test will show
the:
1. Safe amount of chlorine that
may be fed without killing
people
2. Number of lbs required to
kill 100% of coliforms
3. Amount of chlorine required
to give a desired residual
after a given time
4. Amount of chlorine required
to satisfy the biochemical
oxygen demand
100%
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...
0%
Breakpoint Chlorination
Breakpoint chlorination: The point at which near complete oxidation of
nitrogen compounds are reached . Any point beyond breakpoint is
mostly free chlorine (HOCL and OCL-)
A. Amount of chlorine required
Theory: 7.6 to 15 times the ammonia nitrogen content of the water
Practice: up to 25 times the ammonia nitrogen content
B. Beyond breakpoint
90% free residual chlorine (HOCL and OCL-)
10% combined chlorine
C. Why must breakpoint chlorination be reached?
• Necessary for the production of free residual chlorine (HOCL and OCL-)
• Reduces taste and odors
• Reduces chloramines
What is the process of adding
chlorine to water until the
chlorine demand has been
satisfied called?
100%
Contact time
Reliquefaction
Hypochlorination
Breakpoint chlorination
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1.
2.
3.
4.
Breakpoint Chlorination
Zone I: Chlorine is destroyed by reducing agents such as
iron, manganese, clay and silt. Chlorine reduced to
chloride
Zone II: Chlorine comes into contact with organics and
ammonia. Chloroorganics and chloramines are formed.
Zone III: Chloroorganics and chloramines are partially
destroyed. Chloramines are broken down and converted to
nitrogen gas which leaves the system
Zone IV: Breakpoint. Beyond this point, free available
residual is formed. Some chloroorganics still remain as
combined residual.
Chlorine demand is difference between applied chlorine and the free chlorine
residual at any two points on the breakpoint curve.
In Zone 1 most of the chlorine
dose gets used by chlorine
demand ?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
In Zone II chlorine reacts with
ammonia to form combined
chlorine ?
78%
Fa
ls
e
22%
Tr
ue
1. True
2. False
In Zone III some combined
chlorine gets broken down to
nitrogen gas ?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
At Breakpoint chlorine added
becomes free available chlorine?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
Disinfection with chlorine may
cause the formation of these
compounds. They are a result of
chlorine binding to naturally
occurring organic matter.
Trihalomethanes
Trichloramines
CFCs
Chloroalkali salts
54%
46%
...
0%
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1.
2.
3.
4.
DPB (TRIHALOMETHANES)
• THM: Carcinogenic byproduct of a reaction with chlorine. Form when
free chlorine comes into contact with organic compounds. ID by EPA
in 1974.
A. Four most common THMs
• Chloroform
• Bromodichloromethane
• Dibromochloromethane
• Bromoform
MCLS
0 mg/L
0 mg/L
0.06 mg/L
0 mg/L
C. DPB
• Trihalomethanes, haloacetonitriles, chlorinated acetic acids,
chlorophenolds,
Bromoform is a type of
trihalomethane?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
TRIHALOMETHANES
•Chloroform
•Bromodichloromethane
•Bromoform
•MCL=0.08 mg/L
X
H
C
X
X
HCX3
X= Cl, Br, or I
DPB (TRIHALOMETHANES)
D. Water treatment processes that can be used to control THMs.
• Aeration
• Feed oxidation chemicals instead of pre chlorination
• Coagulation, flocculation, sedimentation, and filtration
• Water softening processes (Ion exchange)
• Powdered activated carbon.
E. Substitute Oxidants for Pre-chlorinations
• Ozone O3
Potassium permangante KMnO4
• Hydrogen peroxide H2O2 hypochlorous acid HOCl
• Hypobromous Acid HOBr Bromine Br
• Hypoiodous acid HOI
Chlorine Dioxide ClO2
• Iodine
I2
Oxygen O2
You can aerate or add oxygen to
water before chlorination to cut
THMS?
1. True
2. False
94%
ls
e
Fa
Tr
ue
6%
Chlorine Effectiveness
These are all important:
1. pH
2. Temperature
3. Chlorine Demand:
4. suspended solids/nitrite/organics/
reduced chemicals
5. Contact time
6. Concentration
7. Mixing Intensity
8. Type of residual
Chlorine Effectiveness
1. pH (low pH =better disinfection)
• want pH < 7.5=more hypochlorus acid
2. Temperature (warm temp=better disinfect)
• chlorine disinfection power doubles every 10
degrees.
3. Chlorine Demand (Low Chlorine
demand=better disinfect)
• Fe+3, Mn+4, HS and turbidity cause chlorine demand
4. Suspended solids/nitrite/organics/
reduced chemicals
As water temperatures decrease,
the disinfecting action of
chlorine
94%
1. Decreases
2. Increases
3. Remains the same
6%
m
e
sa
se
s
th
e
em
ai
ns
R
In
cr
ea
s
se
re
a
ec
D
0%
In the application of chlorine for
disinfection, which of the
following is not normally an
operational consideration?
55%
Mixing
Contact time
Dissolved oxygen
pH
None of these answers
are correct
32%
14%
...
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is
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ta
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on
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e
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...
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tt
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ng
0%
M
1.
2.
3.
4.
5.
pH > 8 favors hypochlorite ion
which is a more powerful
disinfectant than hypochlorous
acid?
1. True
2. False
93%
ls
e
Fa
Tr
ue
7%
Chlorine disinfection power
doubles every 10 degrees?
93%
Fa
ls
e
7%
Tr
ue
1. True
2. False
Low chlorine demand is better
for disinfection?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
Chlorine Effectiveness
5. Contact time (longer contact = better disinfection)
• Varies depending on tank dimensions
6. Concentration (higher concentration=better
disinfection)
• OPTIMIZE THE DISINFECTION PROCESS
7. Mixing Intensity (Rapid Mixing=better disinfection)
• Rapidly disperse chlorine better kill rate
8. Disinfection CT (higher actual CT=better
disinfection)
• As disinfection CT increases by 50, effective kill
increases 10 times (EPA set guidelines)
Longer contact time is better for
disinfection?
100%
Fa
ls
e
0%
Tr
ue
1. True
2. False
In general high dose
concentrations = better
disinfection?
87%
Fa
ls
e
13%
Tr
ue
1. True
2. False
Slow mixing favors better
disinfection?
1. True
2. False
85%
ls
e
Fa
Tr
ue
15%
SDWA
99.9% removal of Giardia Lamblia cysts
99.99% removal of Enteric Viruses
Disinfection CTs have been established
Free chlorine
Chloramine
Chlorine dioxide
Ozone
Log
Understanding “log removal” requirements of the Long Term 1 Enhanced
Surface Water Treatment Rule
First a definition and some examples:
Logarithm10: The exponent of the power to which 10 must be raised to equal a
given number.
Examples:
• 102 is equal to 100, the log10 of 100 is 2
• 103 is equal to 1000, the log10 of 1000 is 3
• 102.65 is equal to 446.7, the log10 of 446.7 is 2.65
Log inactivation: A simplified method for expressing the degree
to which microorganisms are removed from water. The removal
percentage is expressed as the log to the base 10.
Examples:
If 100 Giardia cysts are inactivated so that only 1 remains, what is the percent
removal of the microorganism?
(100 - 1) x 100 = 99% or 2 log inactivation
100
EPA APPROVED METHODS
Inactivation of Waterborne Pathogens By Disinfection
The EPA has approved 4 chemical oxidizers for drinking
water
Disinfection:
1. Free Chlorine, (HOCl and OCl-)
2. Chloramine, (NH2Cl)
3. Chlorine dioxide, (ClO2)
4. Ozone (O3)
Each of these disinfectants has a proven capability to kill or
inactivate waterborne pathogens, including viruses and
protozoa cysts. The disinfection power of these chemicals
is dramatically different.
Disinfection C•T
Four EPA Approved disinfectant chemicals are
Free Chlorine, (HOCl and OCl-)
Chloramine, (NH2Cl)
Chlorine dioxide, (ClO2)
1. True
Ozone (O3)?
100%
Fa
ls
e
0%
Tr
ue
2. False
Disinfection C•T Requirements
Chlorine residual concentrations (mg/L)
Contact Time (min)
Water Temperature
Water pH
Disinfection power= [residual chlorine] • time of its contact
Disinfection C•T Calculation
C•T= [disinfection concentration mg/L] • contact time (min)
C•T units= mg/L• min or mg •min/L
Required C•T
CTrequired is # established by EPA to provide log
inactivation. Based on Giardia cysts. Look up in charts
Actual C•T
CTactual is # established by multiplying actual chlorine
residual by hydraulic detention time and baffle factor.
Disinfection C•T Calculation
C•T actual =[Residual chlorine]•hydraulic detention time•baffle factor (table)
Hydraulic detention time = volume/flow rate
C•Tact/ CTreq= ratio must be > or = to 1.
C•Tact/ CTreq>1.0
Disinfection C•T Rules
1.Chlorine residuals used for C•T
calculations are measured after
contact, but before first customer.
2. Contact times are determined by
calculating the hydraulic detention
time (HDT) as water flows through
pipes and tanks. Based on highest
flow of day.
Disinfection C•T Rules
3. Water flowing through pipes provides
contact times that are equal to the
calculated HDT. Circular or rectangular
tanks used for contact time are given
only partial credit due to short
circuiting.
The objective stated in the syllabus to
have an overview of chlorine
chemistry and the chlorination
process, were met ?
Strongly Agree
Agree
Disagree
Strongly Disagree
0%
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ee
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1.
2.
3.
4.