C.T CalculationC.T Calculation

Math for Water TechnologyMTH 082(pg. 468)

Math for Water TechnologyMTH 082(pg. 468)

“Required by Law”“Required by Law”

C.T calculationC.T calculation

• “C” is the concentration of chlorine,

• “T” is the amount of time the water has been in contact with chlorine before the first user.

• Calculated daily and compared against the EPA CT “Required” Table

• “C” is the concentration of chlorine,

• “T” is the amount of time the water has been in contact with chlorine before the first user.

• Calculated daily and compared against the EPA CT “Required” Table

EPA rules states - “Measurements must be taken on the same day of the week, every week, for one year (52 measurements), during peak hourly flow for that day. Data can be measured manually or with on-line instrumentation.”

C.T calculationC.T calculation

• Surface Water Treatment Rule: all surface water and GWUDI systems require 99.9% (3-log removal) and/or inactivation of Giardia and 99.99% (4-log) removal of viruses through disinfection and treatment

• Ground Water Treatment Rule: If a system is fecal positive may be required to achieve inactivation of 99.99% (4-log) removal of viruses through disinfection and treatment

• Surface Water Treatment Rule: all surface water and GWUDI systems require 99.9% (3-log removal) and/or inactivation of Giardia and 99.99% (4-log) removal of viruses through disinfection and treatment

• Ground Water Treatment Rule: If a system is fecal positive may be required to achieve inactivation of 99.99% (4-log) removal of viruses through disinfection and treatment

C.T Calculation ProblemsC.T Calculation Problems

• To calculate the contact time T, the results of a recent tracer study must be used!!

• The peak flow must be measured from the effluent side of the clearwell or contact chamber, NOT the flow through the plant.

• The chlorine residual, pH, and temperature values used to calculate CT must be measured at the effluent side of the clearwell or contact chamber, or before the first user.

• To calculate the contact time T, the results of a recent tracer study must be used!!

• The peak flow must be measured from the effluent side of the clearwell or contact chamber, NOT the flow through the plant.

• The chlorine residual, pH, and temperature values used to calculate CT must be measured at the effluent side of the clearwell or contact chamber, or before the first user.

CT Calculation ProblemsCT Calculation Problems

• When using the EPA CT tables, make sure you

round down for temperature, and

round up for pH.• log-reduction must equal 3.0 for Giardia

• When using the EPA CT tables, make sure you

round down for temperature, and

round up for pH.• log-reduction must equal 3.0 for Giardia

For surface water systems without filtration, the Surface Water

Treatment Rule requires public water systems to?

For surface water systems without filtration, the Surface Water

Treatment Rule requires public water systems to?

Pro

vide

coag

ul...

Mai

ntain

a C

...

Contin

uously

s...

Mai

ntain

publi.

..

3% 0%

30%

67%

1. Provide coagulation and filtration

2. Maintain a C X T value above the minimum value

3. Continuously sample for total coliforms

4. Maintain public notification

1. Provide coagulation and filtration

2. Maintain a C X T value above the minimum value

3. Continuously sample for total coliforms

4. Maintain public notification

In the application of chlorine for disinfection, which of the following is

not normally an operational consideration?

In the application of chlorine for disinfection, which of the following is

not normally an operational consideration?

Mix

ing

Conta

ct ti

me

Dis

solv

ed o

xyg...

pH

None

of the

se ..

.

7%0%

7%4%

82%1. Mixing

2. Contact time

3. Dissolved oxygen

4. pH

5. None of these answers are correct

1. Mixing

2. Contact time

3. Dissolved oxygen

4. pH

5. None of these answers are correct

The chlorine residual, pH, and temperature values used to

calculate CT must be measured at?

The chlorine residual, pH, and temperature values used to

calculate CT must be measured at?

effl

uent s

ide

...

effl

uent s

ide

...

bef

ore th

e fir

...

Any

of the

abo.

..

35%

46%

19%

0%

1. effluent side of the clearwell

2. effluent side of the contact chamber

3. before the first user

4. Any of the above would be ok

1. effluent side of the clearwell

2. effluent side of the contact chamber

3. before the first user

4. Any of the above would be ok

The C.T calculation must be calculated

The C.T calculation must be calculated

Once

a y

ear

Once

a m

onth

Once

a w

eek

Once

a d

ay

0%

84%

13%3%

1. Once a year

2. Once a month

3. Once a week

4. Once a day

1. Once a year

2. Once a month

3. Once a week

4. Once a day

The peak flow must be measured as total flow through

the plant?

The peak flow must be measured as total flow through

the plant?

Tru

e

Fal

se

58%

42%

1. True

2. False

1. True

2. False

The final C.T calculation has what units?

The final C.T calculation has what units?

Mg/L

Lbs/

day

mg-

min

/L

tim

e

12%4%

81%

4%

1. Mg/L

2. Lbs/day

3. mg-min/L

4. time

1. Mg/L

2. Lbs/day

3. mg-min/L

4. time

What is the acceptable log reduction for Giardia?

What is the acceptable log reduction for Giardia?

1 2 3 4

0%

17%

83%

0%

1. 1

2. 2

3. 3

4. 4

1. 1

2. 2

3. 3

4. 4

What is the acceptable log reduction for viruses?

What is the acceptable log reduction for viruses?

1 2 3 4

0%

94%

0%6%

1. 1

2. 2

3. 3

4. 4

1. 1

2. 2

3. 3

4. 4

Four log removal is?Four log removal is?

90.0

0%

99.0

0%

99.9

0%

99.9

9%

0%

83%

17%

0%

1. 90.00 %

2. 99.00 %

3. 99.90 %

4. 99.99 %

1. 90.00 %

2. 99.00 %

3. 99.90 %

4. 99.99 %

If your temperature is 8 degrees with a pH of 7.2, you should use the ____ degree page and the _____ pH table

(please look at your tables).

If your temperature is 8 degrees with a pH of 7.2, you should use the ____ degree page and the _____ pH table

(please look at your tables).

5, 1

9

10,

8.5

5, 7

.5

10,

7

0%5%

95%

0%

1. 5, 19

2. 10, 8.5

3. 5, 7.5

4. 10, 7

1. 5, 19

2. 10, 8.5

3. 5, 7.5

4. 10, 7

Disinfection CTs have been established for?

Disinfection CTs have been established for?

Fre

e ch

lorin

e

Chlo

ram

ine

Chlo

rine

dioxi

de

Ozo

ne

All

of the

above

3% 0%

93%

3%0%

1.Free chlorine

2.Chloramine

3.Chlorine dioxide

4.Ozone

5.All of the above

1.Free chlorine

2.Chloramine

3.Chlorine dioxide

4.Ozone

5.All of the above

Disinfection C.T are impacted by which of the

following?

Disinfection C.T are impacted by which of the

following?

Chlo

rine

resi

dual c

o...

Conta

ct T

ime

(min

)

Wat

er T

emper

ature

Wat

er p

H

All

of the

above

0% 0%

100%

0%0%

1. Chlorine residual concentrations (mg/L)

2. Contact Time (min)

3. Water Temperature

4. Water pH

5. All of the above

1. Chlorine residual concentrations (mg/L)

2. Contact Time (min)

3. Water Temperature

4. Water pH

5. All of the above

T =contact time= Detention TimeT =contact time= Detention Time

“the length of time water is retained in a vessel or basin ”

“the length of time water is retained in a vessel or basin ”

C.T CalculationC.T Calculation

The units of T in the final CT calculation are ?

The units of T in the final CT calculation are ?

Sec

onds

Min

utes

Hours

Day

s

5% 0%0%

95%

1. Seconds

2. Minutes

3. Hours

4. Days

1. Seconds

2. Minutes

3. Hours

4. Days

Determining T in CT?Determining T in CT?

Detention time (DT) = volume of tank = MG (1440min)

flow rate MGD (1day)

Want T value to be in minutes

Detention time (DT) = volume of tank = MG (1440min)

flow rate MGD (1day)

Want T value to be in minutes

T = volume X Baffle Factor (table)

flow rate

T = volume X Baffle Factor (table)

flow rate

Baffle Factor?Baffle Factor?

in out

Poor circulation Baffling efficiency = 5-10%Poor circulation Baffling efficiency = 5-10%

in out

Poor circulation Baffling efficiency = 5-10%Poor circulation Baffling efficiency = 5-10%

in out

No circulation Baffling efficiency = 0%No circulation Baffling efficiency = 0%

Baffle Factor?Baffle Factor?

in

No circulation Baffling efficiency = 0%No circulation Baffling efficiency = 0%

in out

Good circulation Baffling efficiency = 30-50%Good circulation Baffling efficiency = 30-50%

Superior circulation Baffling efficiency = 70%Superior circulation Baffling efficiency = 70%

in out

Baffle Factor?Baffle Factor?Perfect circulation Baffling efficiency = 100%Perfect circulation Baffling efficiency = 100%

Poor circulation/hydropneumatic tankBaffling efficiency = 10%Poor circulation/hydropneumatic tankBaffling efficiency = 10%

No circulation/Bladder type pressure tankBaffling efficiency = 0%No circulation/Bladder type pressure tankBaffling efficiency = 0%

in out

in out

Baffle Factor?Baffle Factor?

Unbaffled Tank 0.1

Poor Baffling 0.3

Average Baffling 0.5

Superior baffling 0.7

Pipe Flow 1.0

“How well the chlorine is in contact with the water”“How well the chlorine is in contact with the water”

What is the average detention time in a basin that is 1240 ft3

when the flow rate is 4.1 MGD?

3.3

min

.03

min

303

min

435

,512

min

85%

15%

0%0%

1. 3.3 min

2. .03 min

3. 303 min

4. 435,512 min

What is the average detention time in a basin given the

following: diameter = 80' depth = 12.2' flow = 5 MGD

132

min

101

min

144

min

105

min

93%

7%0%0%

1. 132 min

2. 101 min

3. 144 min

4. 105 min

Determine T at the effluent side of a superior baffled contact chamber basin that has the

following: diameter = 30' depth = 15' flow = 700 gpm

65.

8 m

in.

79.

1 m

in

75

min

.

86.

1 m

in.

0% 0%0%

100%1. 65.8 min.

2. 79.1 min

3. 75 min.

4. 86.1 min.

DRAW:•Given:•Formula:•Solve:

DRAW:•Given:•Formula:•Solve:

Determine T at the effluent side of a superior baffled contact chamber basin that has the following: Length

of = 30ft, width of 20 ft, depth = 15' flow = 700 gpm?

Determine T at the effluent side of a superior baffled contact chamber basin that has the following: Length

of = 30ft, width of 20 ft, depth = 15' flow = 700 gpm?

96.

17 m

in

67.

32 m

in

12.

85 m

in

9 m

in

15%

0%0%

85%

tank= L X W X D , Flow rate 700 gpm, BF=0.7T= DT X BFT= volume of tank/flow rate X BFVt= L X W X DVt=30 ft X 20 ft X 15 ft= 9000 ft3

9000 ft3 (7.48 gal/1ft3)= 67320 galDT=VT/FR X BFTime = 67,320 gal/700gpm X 0.7Time= 96.17 min X 0.7Time= 67.32 min

tank= L X W X D , Flow rate 700 gpm, BF=0.7T= DT X BFT= volume of tank/flow rate X BFVt= L X W X DVt=30 ft X 20 ft X 15 ft= 9000 ft3

9000 ft3 (7.48 gal/1ft3)= 67320 galDT=VT/FR X BFTime = 67,320 gal/700gpm X 0.7Time= 96.17 min X 0.7Time= 67.32 min

in 700 gpmout

30 ft

20 ft

15 ft

1. 96.17 min

2. 67.32 min

3. 12.85 min

4. 9 min

1. 96.17 min

2. 67.32 min

3. 12.85 min

4. 9 min

Disinfection C•T Requirements Disinfection C•T Requirements Chlorine residual concentrations (mg/L)

Contact Time (min)

Water Temperature

Water pH

Disinfection power= [residual chlorine] • time of its contact

Chlorine residual concentrations (mg/L)

Contact Time (min)

Water Temperature

Water pH

Disinfection power= [residual chlorine] • time of its contact

Disinfection C•T CalculationDisinfection C•T CalculationC•T= [disinfection concentration mg/L] • contact time (min)

C•T units= mg/L• min or mg •min/L

Required C•TCTrequired is # established by EPA to provide log inactivation. Based on Giardia

cysts. Look up in charts

Actual C•TCTactual is # established by multiplying actual chlorine residual by hydraulic

detention time and baffle factor.

C•T= [disinfection concentration mg/L] • contact time (min)

C•T units= mg/L• min or mg •min/L

Required C•TCTrequired is # established by EPA to provide log inactivation. Based on Giardia

cysts. Look up in charts

Actual C•TCTactual is # established by multiplying actual chlorine residual by hydraulic

detention time and baffle factor.

Disinfection C•T CalculationDisinfection C•T CalculationC•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

“You want to make sure that you are actually meeting the necessary requirements”

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

“You want to make sure that you are actually meeting the necessary requirements”

Disinfection C•T RulesDisinfection C•T Rules1.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.

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 RulesDisinfection 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.

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.

Table 7.2: Typical Removal Credits and Inactivation Requirements for Various Treatment Technologies

ProcessTypical Log

Removal CreditsResulting

Disinfection LogInactivation

Requirements

Giardia Viruses Giardia Viruses

ConventionalTreatment

2.5 2.0 0.5 2.0

DirectFiltration

2.0 1.0 1.0 3.0

Slow SandFiltration

2.0 2.0 1.0 2.0

DiatomaceousEarth Filtration

2.0 1.0 1.0 3.0

Unfiltered 0 0 3.0 4.0

* Systems must demonstrate to the State by pilot study or other meansthat the alternative filtration technology provides the required logremoval and inactivation shown in Table 7-1.