4 Calculate the time for 99 2log removal via natural inactiv

4. Calculate the time for 99% (2-log) removal via natural inactivation of Cryptosporidium from water at a typical winter-time temperature of lakes here in Southern California of 12^oC.

Solution

For 2 log removal of Cryptosporidium at 12 degree celcius temperature, lets assume the concentration of chlorine in lake is 1.8 mg/L. So at pH 7 of water,

CT = C x T where C is concentration of disinfectant in mg/L and T is Actual detention time in minutes.

value of CT = 122 and C = 1.8 mg/L

122=1.8 x T

T = 122/1.8

T = 67.7 or 68 min mg/L