Disinfection of Water Contaminated with Fecal Coliform Using Ozone: An Evaluation of the Effect of Ozone Dose and Contact Time JHRC

Introduction and purpose: Chlorine, due to its residual effect, has an important role in water disinfection. However, its by-products, which could be harmful to consumers’ health, has led the researchers to investigate the use of other methods or materials for disinfection. The aim of this study was to evaluate the performance of ozone in disinfection of Escherichia coli (an index of fecal pollution) contaminated water. Methods: E. coli was used for contaminated water preparation. Culture and counting methods were performed based on the book entitled “The Standard Methods of Water and Wastewater” and were recorded with colony forming unit (CFU)/ml. Normality of the data was analyzed using Kolmogorov- smirnov test, and t-test and ANOVA were performed to analyze the data. Results: The results showed that destruction of E. coli increased by increasing ozone concentration and decreasing bacteria’s density. Removal efficiency of the 1 mg/L dose, as compared to the 5 mg/L dose of ozone, in densities of 10 4 and 10 5 CFU/ml was significant (P-value<0.05). The statistical results demonstrated that removal efficiency of bacteria with a number of 10 5 CFU/ml, at the contact time of 1 min versus 5,10 and 20 min was significant (P<0.05). The removal efficiency of E. coli at the contact time of 10 min and above, reached 100%. Conclusion: Ozone, due to its oxidizing effect on microorganisms, has good disinfectant properties. The results of this study suggest that ozone can be significantly effective in disinfecting water contaminated with E. coli.