Q14496 - INFO: CT
CT - Math Toolbox function returns the CT Required for Inactivation of Giardia Cysts for a given Disinfectant, Log Inactivation, Temperature, pH, and Disinfectant Residual from the EPA lookup tables.

SYNTAX:

CT(InactivationOf, Disinfectant, LogInactivation, Temp, pH, Cl2)

InactivationOf – Set 1 for Giardia or 2 for Viruses.

Disinfectant – Set to a number based on the following (i.e. set to 1 for Free Chlorine)

1 - Free Chlorine
2 - Chlorine Dioxide
3 - Chloramine
4 - Ozone

Log Inactivation - .5, 1, 1.5, 2, 2.5,3, or 4 (4 only applies to inactivation of Viruses)

Temperature – Water Temperature in Deg C

pH – pH of the water (only required for Inactivation of Giardia by Free Chlorine)

Cl2 – Chlorine Residual at end of disinfection segment in mg/L. Only used for Inactivation of Giardia by Free Chlorine, for all other lookups use -1 to indicate not used.

EXAMPLES

=CT(1,1,2,15,7.5,1) returns 60 from EPA CT Table C-4.

=CT(1,2,3,15,7.5,-1) returns 19 from EPA Table C-8.  CT Required for 3 Log Inactivation of Giardia (1) by Chlorine Dioxide (2) at 15 Deg C with a pH between 6 and 9 (7.5).

Handling of Temperatures above 25:

Calculate the 0.5 log inactivation of Giardia Cysts by Ozone from EPA Table C-12 with a temperature of 30 Deg C.  Option 1, set temperature to 25 and return the CT Required for 0.5 and temp of 25:

=CT(1,4,.5,IF(V13105>25,25,V13105),1,1)

where V13105 is the Temperature in Deg C.

For Texas, based on rg-211 manual states "For temperatures above 25°C, CTrequired drops by a factor of two for each 10°C rise in temperature—that is, the CTrequired at 30°C is one-half the CTrequired at 20°C."   This can be accomplished with the following equation.  Note, the 0.08 is the CTrequired for 0.5 @ 25 Deg C.

=if(V13105<=25,CT(1,4,.5,V13105,1,1),.08-(((V13105-25)/10)* .5*.08))

where V13105 is the Temperature in Deg C
0.08 is the CTrequired for 0.5 @ 25 Deg C