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C . T Calculation

C . T Calculation. Math for Water Technology MTH 082 (pg. 468). “Required by Law”. 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.

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C . T Calculation

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  1. C.T Calculation Math for Water Technology MTH 082 (pg. 468) “Required by Law”

  2. 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 • 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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

  9. The C.T calculation must be calculated • Once a year • Once a month • Once a week • Once a day

  10. The peak flow must be measured as total flow through the plant? • True • False

  11. The final C.T calculation has what units? • Mg/L • Lbs/day • mg-min/L • time

  12. What is the acceptable log reduction for Giardia? • 1 • 2 • 3 • 4

  13. What is the acceptable log reduction for viruses? • 1 • 2 • 3 • 4

  14. Four log removal is? • 90.00 % • 99.00 % • 99.90 % • 99.99 %

  15. 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

  16. Disinfection CTs have been established for? • Free chlorine • Chloramine • Chlorine dioxide • Ozone • All of the above

  17. 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

  18. T =contact time= Detention Time C.T Calculation “the length of time water is retained in a vessel or basin”

  19. The units of T in the final CT calculation are ? • Seconds • Minutes • Hours • Days

  20. 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

  21. 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

  22. in out Baffle Factor? No circulation Baffling efficiency = 0% in Good circulation Baffling efficiency = 30-50% out in Superior circulation Baffling efficiency = 70%

  23. 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%

  24. Baffle Factor? “How well the chlorine is in contact with the water”

  25. 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

  26. 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

  27. 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.

  28. 30 ft 20 ft 15 ft in 700 gpm out 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: • 96.17 min • 67.32 min • 12.85 min • 9 min tank= L X W X D , Flow rate 700 gpm, BF=0.7 T= DT X BF T= volume of tank/flow rate X BF Vt= L X W X D Vt=30 ft X 20 ft X 15 ft= 9000 ft3 9000 ft3 (7.48 gal/1ft3)= 67320 gal DT=VT/FR X BF Time = 67,320 gal/700gpm X 0.7 Time= 96.17 min X 0.7 Time= 67.32 min

  29. Disinfection C•T Requirements Chlorine residual concentrations (mg/L) Contact Time (min) Water Temperature Water pH Disinfection power= [residual chlorine] • time of its contact

  30. 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 CTrequiredis # established by EPA to provide log inactivation. Based on Giardia cysts. Look up in charts Actual C•T CTactualis # established by multiplying actual chlorine residual by hydraulic detention time and baffle factor.

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

  32. Disinfection C•T Rules • 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.

  33. 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.

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

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