Inactivation Of Virus In Drinking Water By Three Chlorine-Containing Disinfectants And Its Pseudo-Kinetics

The control of pathogenic microbes is one of the paramount aspects for drinking water safety. Public accidents caused by viruses in drinking water, given their relatively smaller size and greater pathogenicity than other microorganisms, were reported now and then during these years, which we should pay enough attention to. However, only several countries have regulated viruses in their drinking water guidelines, while China had no limitations to viruses in new-enacted Standards for Drinking Water Quality (GB5749-2006). Furthermore, most researches about virus inactivation focused on the fields of hygiene or hospital disinfection, the results of which could offer little guidance to drinking water disinfection processes. As a result, researches about virus disinfection for drinking water are in urgent need.With the purpose of establishing effective drinking water disinfection technology for viruses in slightly contaminated water, this study systematically compared the impact and pseudo-kinetics of virus inactivation by free chlorine, chloramines and chlorine dioxide with MS2 coliphage as indicators. At the same time, the influence of water types, such as filtered water and source water in drinking water plant, on disinfection efficiency and the inactivation laws was also studied.The results of free chlorine inactivating MS2 phages showed that, in deionized water, when the initial dosage of free chlorine was≤0.5 mg/L, the titer of viruses decreased by 3 log and then kept stable; when the dosage was≥1.0 mg/L, viruses could be inactivated to below detection limit in only one minute, and the time needed to totally inactivate viruses got shorter with the increase of initial dosages. The Ct value (product of the concentration of residual disinfectant and the contact time, mg·L-·1min) needed to achieve USEPA standards, namely 4 log and 99.99% inactivation, was 3.80 mg·L-1·min. Besides, slightly contaminated waters had tremendous influence on MS2 inactivation by free chlorine based on the results that Ct values needed to achieve USEPA standards decreased in turn in deionized water, filtered and raw water. Free chlorine decayed in accordance with first-order kinetics, while aberrancy occurred and decay rates greatly declined when disinfectant reacted with organic matters or ammonia in slightly contaminated waters. Furthermore, when free chlorine dosage was abundant compared to the total amount of disinfection demand and impurity consumption, the survival curves were linear and could be described by first-order Chick model or Chick-Watson model; when the dosage was relatively insufficient, the survival curves were biphasic or upward concave and could only be simulated by Hom model or Selleck model which were suitable for non first-order kinetic laws.The results of chloramines inactivating MS2 phages showed that, in deionized water, titer of viruses kept stable at normal dosage; prominent inactivation was obtained when initial dosage was≥10 mg/L; the titer of viruses decreased respectively by 0.5 log and 1.5 log at 10 mg/L and 20 mg/L with 1 h contact time, which could not achieve USEPA standards. Viruses were inactivated to below detection limit in 5 min at 30 mg/L, but this probably resulted from residual free chlorine at the very beginning of disinfection. Slightly contaminated water had some impact on MS2 inactivation but there was no prominent discipline. In three water types, chloramines decayed in agreement with non first-order kinetics and the more contaminated the more divergent from first-order kinetics. The decay rate constant of chloramines was an order of magnitude smaller than that of free chlorine, which indicated chloramines decayed far more slowly than free chlorine did. Most of the survival curves were biphasic or upward concave and only could be simulated by Hom model and Selleck model.The results of chlorine dioxide inactivating MS2 phages showed that, in deionized water, the titer of viruses decreased by 1 log and then kept stable at the initial dosage of 0.1 mg/L; when the dosage was6≥0.175 mg/L, the titer of viruses kept declining for a certain time and the decline rates increased with the increase of initial dosages. When the initial dosage was≥1.0 mg/L, viruses could be inactivated to below detection limit within only one minute. The Ct value needed to achieve USEPA standards was 26.4 mg·L-1·1·min. Slightly contaminated waters also had great impact on MS2 inactivation by chlorine dioxide based on the results that Ct values needed to achieve standards were 54.2 mg·L-1·min and 65.0 mg·L-1·min respectively in filtered and raw water. Furthermore, the impurities in water also influenced the inactivation efficacy in that the reaction were faster in slightly contaminated water than in deionized water at the very beginning of inactivation. Chlorine dioxide decayed in accordance with first-order kinetics and its inactivation kinetics was similar to that of free chlorine.The result of investigation of virus occurrence in outflow of various process units in drinking water plants showed that, the concentrations of MS2 andΦX174 coliphages were approximately 103～104 PFU/100L (PFU, Plaque Forming Unit) in both raw waters of River I and RiverⅡ, which indicated certain possibility of the presence of enteric viruses. The titers of these two phages slightly increased after bio-pretreatment and the removal/inactivation rate achieved 98% after coagulation, sedimentation and biological activated carbon. There were not neither MS2 norΦX174 detected in disinfection outflow and final effluent of both drinking water plants.