C.T Calculation

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C.T Calculation
Required by Law

• Math for Water Technology
• MTH 082
• (pg. 468)

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C.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

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.
3
C.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.

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CT 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

5
For surface water systems without filtration, the
Surface Water Treatment Rule requires public
water systems to?

• Provide coagulation and filtration
• Maintain a C X T value above the minimum value
• Continuously sample for total coliforms
• Maintain public notification

6
In the application of chlorine for disinfection,
which of the following is not normally an
operational consideration?

• Mixing
• Contact time
• Dissolved oxygen
• pH
• None of these answers are correct

7
The chlorine residual, pH, and temperature values
used to calculate CT must be measured at?

• effluent side of the clearwell
• effluent side of the contact chamber
• before the first user
• Any of the above would be ok

8
The C.T calculation must be calculated

• Once a year
• Once a month
• Once a week
• Once a day

9
The peak flow must be measured as total flow
through the plant?

• True
• False

10
The final C.T calculation has what units?

• Mg/L
• Lbs/day
• mg-min/L
• time

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What is the acceptable log reduction for Giardia?

• 1
• 2
• 3
• 4

12
What is the acceptable log reduction for viruses?

• 1
• 2
• 3
• 4

13
Four log removal is?

• 90.00
• 99.00
• 99.90
• 99.99

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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, 19
• 10, 8.5
• 5, 7.5
• 10, 7

15
Disinfection CTs have been established for?

• Free chlorine
• Chloramine
• Chlorine dioxide
• Ozone
• All of the above

16
Disinfection C.T are impacted by which of the
following?

• Chlorine residual concentrations (mg/L)
• Contact Time (min)
• Water Temperature
• Water pH
• All of the above

17
T contact time Detention Time
C.T Calculation
the length of time water is retained in a vessel
or basin
18
The units of T in the final CT calculation are ?

• Seconds
• Minutes
• Hours
• Days

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Determining T in CT?

• 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
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Baffle Factor?
Poor circulation Baffling efficiency 5-10
out
in
Poor circulation Baffling efficiency 5-10
out
in
No circulation Baffling efficiency 0
out
in
21
Baffle Factor?
No circulation Baffling efficiency 0
in
Good circulation Baffling efficiency 30-50
out
in
Superior circulation Baffling efficiency 70
22
Baffle Factor?
Perfect circulation Baffling efficiency 100
in
out
Poor circulation/hydropneumatic tank Baffling
efficiency 10
in
out
No circulation/Bladder type pressure
tank Baffling efficiency 0
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Baffle Factor?
How well the chlorine is in contact with the
water
24
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

25
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

26
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 min.
• 79.1 min
• 75 min.
• 86.1 min.

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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?

• DRAW
• Given
• Formula
• Solve

tank L X W X D , Flow rate 700 gpm, BF0.7 T
DT X BF T volume of tank/flow rate X BF Vt L X
W X D Vt30 ft X 20 ft X 15 ft 9000 ft3 9000
ft3 (7.48 gal/1ft3) 67320 gal DTVT/FR X BF Time
67,320 gal/700gpm X 0.7 Time 96.17 min X
0.7 Time 67.32 min

• 96.17 min
• 67.32 min
• 12.85 min
• 9 min

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Disinfection CT Requirements

• Chlorine residual concentrations (mg/L)
• Contact Time (min)
• Water Temperature
• Water pH
• Disinfection power residual chlorine time of
  its contact

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Disinfection CT Calculation

• CT disinfection concentration mg/L contact
  time (min)
• CT units mg/L min or mg min/L
• Required CT
• CTrequired is established by EPA to provide log
  inactivation. Based on Giardia cysts. Look up in
  charts
• Actual CT
• CTactual is established by multiplying actual
  chlorine residual by hydraulic detention time and
  baffle factor.

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Disinfection CT Calculation

• CT actual Residual chlorinehydraulic
  detention timebaffle factor (table)
• Hydraulic detention time volume/flow rate
• CTact/ CTreq ratio must be gt or to 1.
• CTact/ CTreq gt 1.0
• You want to make sure that you are actually
  meeting the necessary requirements

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Disinfection CT Rules

• Chlorine residuals used for CT 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.

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Disinfection CT 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.

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