Measuring Inactivation of Bacteria in Water by Disinfectants

• Activity Number: 300
• Type: Contributed
• Date/Time: Tuesday, August 5, 2003 : 2:00 PM to 3:50 PM
• Sponsor: Biometrics Section
• Author(s): Shailendra N. Banerjee*+ and Laura Rose and Rodney Donlan and Bette Jensen and Alicia Peterson and Ricardo Murga and Matthew Arduino
• Companies: Centers for Disease Control and Prevention and Centers for Disease Control and Prevention and Centers for Disease Control and Prevention and Centers for Disease Control and Prevention and Centers for Disease Control and Prevention and Centers for Disease Control and Prevention and Centers for Disease Control and Prevention
• Keywords: inactivation ; nonlinear ; viable ; disinfectant

Abstract

Inactivating harmful organisms in drinking water is a major objective to prevent waterborne illness. Ct values (disinfectant concentration x exposure time) are used to judge the efficacy of disinfectants to inactivate various microorganisms in or on different media, e.g., water, surfaces. Experiments were conducted to observe the inactivating effect of chlorine on various pathogenic bacteria. Known bacterial cell concentrations were added to chlorine demand-free buffered water (pH 7.0) containing 0.25, 0.50, 1.00 mg/L free available chlorine held at either 5°C or 25°C. Viable cell counts of bacteria were measured after different exposure times. A nonlinear model was used to express the proportion of viable cells of bacteria remaining after disinfectant treatment, at a given time, as a function of chlorine concentration (C), exposure time (t), and temperature. The estimated Ct values decreased with increasing temperature. Thus, for 99% inactivation of bacterium A, Ct was 0.67 mg-min/L at 5°C, 0.24 mg-min/L at 15°C, and 0.09 mg-min/L at 25°C. Similarly, for bacterium B, the respective values for Ct at 5°C, 15°C, and 25°C were 11.30 mg-min/L, 5.53 mg-min/L, and 2.70 mg-min/L. The model was able to predict the Ct value for 99% inactivation of these bacteria at any given temperature.