The Code of Federal Regulations provides tables of Ct values for 99.9% inactivation at v...

The Code of Federal Regulations provides tables of Ct values for 99.9% inactivation at various temperatures and pH values (10 CFR 141.74 and 10 CFR 141.720). To determine the Ct value for another inactivation percentage, the following equation is suggested in the Guidance Manual (U.S. EPA, 1991):

Another method to determine log inactivation credits at intermediate or extrapolated values is with the use of the Chick-Watson law. Using a spreadsheet you have written and the following data from the Guidance Manual, determine the inactivation rate constant and determine the percent error in estimating Ct for a 94.38% inactivation of Giardia with chlorine at a temperature of 10^oC and a pH of 7.0. The following data were extracted from the Guidance Manual at a temperature of 10^oC, a pH of 7.0, and a chlorine dose of 1.6 mg/L.