Chlorine Disinfection of Low Temperature Waters

This study evaluated chlorine disinfection of water at controlled temperatures of 0.5°C, 4°C, 8°C, 12°C, 16°C, and 20°C. Bacterial tests were made by the membrane filter technique. The indicator bacteria were a pure culture of E. coli. In the 0°C-8°C temperature range, the quantity of chlorine necessary to achieve a desired level of disinfection is dependent solely on the numbers of E. coli initially present in the water. Alkalinity (as CaCO₃) in the 0-100 mg/l range and pH in the 6-8 range have no statistically significant effect on the chlorine disinfection rate in the 0-12°C temperature range. Calcium in the water in concentrations as low as 1 mg/l reduces the rate of chlorine disinfection. The data and findings from the study were used to develop a model for plant operators showing the chlorine dose required to achieve a desired level of disinfection for E. coli concentrations in the ranges, 5 × 10⁷, 5 × 10⁵, and 5 × 10³ or less per 100 ml.