Inactivation Dynamics of Gram-negative and Gram-positive Microbes in Drinking Water: a Comparative Study of Chlorine and Monochloramine Disinfection

Abstract

To assure the prevention of microbial contamination and the provision of safe potable water to consumers, efficient disinfection is the final barrier. Chlorine, once a widely applied disinfectant, has essentially been re-considered by many water treatment practitioners. Since the research unveiled chlorine-associated health repercussions, the investigation shifted to more viable disinfection options such as the use of monochloramines, that remains active in the system for relatively long periods. Keeping in view, the present study compared the biocidal competence of chlorine and monochloramine to inactivate the gram-negative Klebsiella pneumoniae and Pseudomonas aeruginosa along with the gram-positive Staphylococcus aureus. A lab-scale testing batch was set up in carefully monitored conditions to investigate the response of these bacterial species to the applied disinfection dosages of 1 and 2 mg/L. Moreover, a referenced batch of control evidenced the accuracy of results. A significant difference in the response to chlorine and monochloramine was recorded both in mixed and mono-cultures of bacteria. The bench-scale inactivation experiments revealed that chlorine and monochloramine greatly damaged K. pneumoniae and S. aureus in monocultures. Whereas these bacterial species revealed greater tolerance when acted together in a mixed-cultures and, hence, an overall lower degree of disinfection was achieved. P. aeruginosa exhibited reduced vulnerability to disinfectants in mixed-cultures, marking K. pneumoniae tolerant to chlorine. Most significant correlation between disinfectant species was found at 30 min of exposure with notable logremoval of K. pneumoniae (p = 0.01), P. aeruginosa (p = 0.003) and S. aureus (p = 0.0001). In conclusion, for prolonged exposures, monochloramine is advisable owing to its immediate microbial inactivation upon contact as well as enhanced stability in drinking water networks. The results could predict the pattern of bacterial inactivation in drinking water distribution networks and fill a major gap in the water sector.