Study On The Inactivation Characteristics And Mechanism Of The Chlorine-resistant Bacteria In Drinking Water System

Chlorine disinfection processes are most widely used in water treatment plants inChina. However chlorine-resistant bacteria have been detected resently in thedistribution systems, which could endanger drinking water microbial safety. Toimprove the biological stability of the distribution system, this research studied thedisinfection characteristics of several strains of chlorine-resistant bacteria isolatedfrom real distribution systems, using free chlorine, monochloramine, chlorine dioxideand sequencial chlorination process, respectively, for inactivation. Moreover, theresearch also has explored the mechanism of disinfection of the bacteria.These strains of chlorine-reisitant bacteria were identified as Mycobacteriummucogenicum, Sphingomonas sanguinis and Methylobacterium. They all showed highresistance to chlorine, especially for M. mucogenicum. The CT value of99.9%inactivation for M. mucogenicum by free chlorine was120mg/L min which was260times more than that of Staphylococcus aureus. For Mycobacteria, the effects of eachdisinfectant are: chlorine dioxide> potassium monopersulfate> monochloramine> freechlorine under the same consentration.In disinfection experiment, the bacteria cells were the main reason of disinfectantdecay and the generation of organic chloramines. No organic chloramines formationwas detected with the cell concentration equal to or less than105CFU/mL. Fourdisinfectants had apparently different decay characteristics and organic chloraminesformation behaviors. Free chlorine decayed fastest and formed the highestconcentration of organic chloramines. Monochloramine decayed very slowly andformed limited organic chloramines. Chlorine dioxide did not form organicchloramines although it exhibited a similar decay behavior as free chlorine.Sequential chlorination was a combination of free chlorination andmonochloramination.The formation of organic chloramines was proportional to theinitial concentration of the disinfectant. Meanwhile the presence of organic matterplayed a protective role for the bacteria in disinfection.Different composition of cell membrane might endow M. mucogenicum with high chlorine resistance. Lipid analysis of the cell construction revealed that95.7%ofcell membrane lipid of M. mucogenicum was composed of saturated long chain fattyacids which was4.98times of that of S. aureus. From the Flow cytometry experimentresult,18.62%of M. mucogenicum showed cell membrane structure damage whilethe percentage of S. aureus was87.59%under the same experimental conditions.Theanalysis of chlorine consumption on two bacteria with different chlorine resistanceindicated that higher amount of chlorine consumption was not the direct reason of thechlorine resistance of mycobacteria.