Research On The Separation, Identification And Control Technology Of Chlorine-resistant Bacteria In Water Supply Pipe Network System

Microbial safety is one of the important contents of drinking water quality safety.However,the emergence of chlorine-resistant bacteria brings a great challenge to the disinfection of water supply network system.This study provides a screening and separation method for chlorine-resistant bacteria in urban water supply systems.A chlorine-tolerant strain was isolated from the Yellow River water supply pipe network system by this method.It was identified as Pseudomonas peli by 16 S rRNA gene analysis.The Pseudomonas peli-isolated resistance to free chlorine was compared with that of standard strains(BNCC:139697),and the disinfection characteristics of free chlorine,chlorine dioxide and uv radiation-inactivated Pseudomonas peli-isolated were studied.At the same time,the disinfectant kinetic relationship of three sterilizing methods for inactivated Pseudomonas peli-isolated was described by using disinfection model.In addition,the relationship between chlorine-resistant bacteria biofilm and chlorine-resistant mechanism was investigated by flow cytometry combined with biological electron microscope.The main results are as follows:(1)Through the screening and separation method of chlorine-resistant bacteria in the urban water supply system provided by this study,the bacteria in the pipe network water in the Yellow River water supply system are enriched.After screening for chlorine resistance,separation and purification,and chlorine resistance verification,a strain of Gram-negative bacteria resistant to acid-free,non-fermenting sugars,and ammonia-free bacteria was screened and identified as Pseudomonas peli by 16 SrDNA.(2)The Pseudomonas peli-isolated had high chlorine tolerance.There was a significant difference between the isolates and the standard strains in their resistance to free chlorine but the isolates were more resistant to chlorine.The CT value of 99.9% free chlorine was 51.26 ～ 90.36 mg ·min / L,which was 1.2 times higher than that of the standard strain and 569 ～ 1004 times higher than that of Escherichia coli.(3)Chlorine dioxide inactivates bacteria faster and more efficiently than free chlorine.The effective inactivation level reached at a given disinfectant dose mainly occurred within the first five minutes of exposure and entered the wake inactivation phasewithin 0.5-2 h after exposure.The disinfectant dose required to inactivate the bacteria increases with the initial concentration of the disinfectant.The level of disinfectant inactivation is positively correlated with the contact time,but the disinfectant concentration and the inactivation efficiency are not linear,and the appropriate disinfectant is selected.The concentration and disinfection contact time can both control the cost of disinfection and ensure the effectiveness of disinfection.(4)The disinfectant dose required to inactivate the bacteria increases with the initial concentration of the disinfectant.The level of disinfectant inactivation is positively correlated with the contact time,but the disinfectant concentration and the inactivation efficiency are not linear,and the appropriate disinfectant is selected.The concentration and disinfection contact time can both control the cost of disinfection and ensure the effectiveness of disinfection.(5)The Hom model can be used to quantitatively describe the disinfectant inactivated Pseudomonas peli from the point of view of kinetics.The disinfection characteristics and tail-dragging effect of Pseudomonas peli strains were considered completely in the hom model.The fitting effect of free chlorine and chlorine dioxide disinfection characteristic curves was better than that of Chick model and Chick-Watson model.The main reasons for the wake effect in the disinfection characteristic curve were the decay of disinfectant concentration with time and the existence of Pseudomonas peliisolated as resistant bacteria.(6)It was found that the biofilm of Pseudomonas peli was significantly related to its chlorine tolerance.Flow cytometry results showed that Pseudomonas peli could maintain a certain cell membrane integrity and permeability under the action of free chlorine,and thicker cell wall is one of the important reasons for its resistance to free chlorine.In addition,the chlorine tolerance of Pseudomonas peli is related to the growth environment,colony morphology and metabolites.The oligotrophic environment domesticated strain can stimulate the strain’s resistance to external unfavorable factors and enhance the chlorine tolerance of the bacteria.This study aimed at the problem that the current method of testing the total numberof bacteria could not screen and separate the chlorogenic bacteria in water,which provided an effective and feasible method for the study of chlorogenic bacteria in urban water supply system.Taking Pseudomonas peli-isolated as an example,the microbial disinfectant resistance and disinfection characteristics in the water supply pipe network were systematically studied.It provides some technical support for the assessment,prevention and control of microbial safety in urban water supply network.