Effect of initial microbial density on inactivation of Escherichia coli by monochloramine

Abstract

Numerous water disinfection studies have reported deviations from the Chick-Watson Law, which was used to develop the Ct tables provided by the USEPA’s SWTR. Some of the modifications of the Chick-Watson Law incorporate explicit dependence on initial microbial density. In this study, a series of inactivation experiments were conducted with Escherichia coli cultured under three different growth conditions to investigate cell density effects on inactivation. Cell density dependent inactivation was observed in E. coli cultures grown on nutrient agar slant overnight and grown in chemostat with hydraulic residence time of 110 h. The disinfection efficiency was significantly (P < 0.05) greater at higher initial microbial density. Inactivation of E. coli cultured in nutrient broth for only 3 h was independent of cell density. These results have a major significance for utilities in terms of optimization of the disinfection process and balancing the risks associated with exposure to pathogens and disinfection/disinfectant byproducts.