ABSTRACT
Objective@#To study the response of Escherichia coli (E. coli) HB101 (plasmid pUC19) and its carried antibiotic resistance genes to the process of cholorination under different environmental conditions.@*Methods@#The E. coli strain was reacted with sodium hypochlorite at the concentration of 0.5, 0.75, 1.00, and 0.55 mg/L, then the residual chlorine and the colonies were detected at the 0.25, 1, 2, 5, 10, 20, and 30 min of the reaction, respectively. The first order disinfection kinetic model and EFH model were used to evaluate the inactivation effect of E. coli (plasmid pUC19) treated by sodium hypochlorite, while the plasmid pUC19 and antibiotic resistance gene ampr were detected by PCR method. Besides, the logarithm of Ct (residual chlorine in t) under different concentration were calculated.@*Results@#The temperature and pH value played important roles on the inactivation of E. coli and elimination of plasmid pUC19 and ampr under the function of sodium hypochlorite. The Ct value needed for 5-log of E.coli HB101(pUC19) inactivation at 4, 20, 36 ℃ was 11.92, 10.28, 7.67, respectively, and when the pH was in 6.0, 7.0, 8.0, with chloride concentration were 0.75, 0.70, 0.55 mg/L, the Ct value needed for reached to 6.68, 10.28, 15.73 min·mg/L. At pH 7.2 condition, when the temperature was 4, 20, 36 ℃, and chloride concentration were 9, 5, 3 mg/L.The required Ct values to completely destroy the transformation function of free antibiotic resistant plasmids were 36.11, 34.17,16.09 min·mg/L. Sodium hypochlorite disinfection can release free ampr gene and even the transformed plasmid pUC19, and pollute the water body. Only when the Ct value reached 903.03 min·mg/L, the complete ampr gene can be destroyed which was far more exceed the bacterial lethal Ct value.@*Conclusion@#Even if all the antibiotic resistant bacteria were inactivated, the antibiotic resistant plasmids or genes might still maintain complete with the transformable function, which may result in new potential risks of waterborne diseases.
ABSTRACT
Objective To observe the efficacy of ozone in the inactivation of f2 phage in water. Methods The concentration of ozone in water was measured by iodometry. During the experiment,the suspension of f2 phage was added in the ozonized water, at 5,15,30 min, the f2 phage inactivation rate was calculated. Results Under the same condition of ventilation,in the range of pH regulated in the drinking water sanitary standard,the effect of pH on the inactivation of f2 phage was not obvious, while the chromaticity of water could remarkably influence the inactivation of f2 phage. Conclusion The higher chromaticity of water can interfere the inactivation of f2 phage in water by ozone.
ABSTRACT
Recently,because of the increasing of nitrogen, phosphate and organic pollutants concentration in water, the population and constitution of microorganisms in water have been influenced. There was a new challenge for the traditional drinking water treatment technology. The studies on the drinking water biostability were summarized and the determination of biological stability of drinking water,the influencing factors on the biostability and the measurement controlling the biostability were introduced in the present paper.