Optimization of bacterial disinfection in drinking water by ozone-induced oxidation-reduction potential control using response surface methodology

This study aimed to determine the optimal oxidation-reduction potential (ORP) and ozonation time to effectively eliminate Escherichia coli and Total coliform from drinking water. An automated ORP control system was implemented, incorporating a Siemens S7-1500 PLC with HMI interface, ORP and pH sensors, a corona discharge ozone generator, and an electric pump (220 V AC, 60 Hz, 30 W) to maintain continuous water circulation at a flow rate of 20 L/min. A response surface methodology (RSM) experimental design with 13 treatments was used to evaluate ORP levels ranging from 550 to 901 mV and ozonation times from 5 to 210 seconds. Tests were conducted in water with a pH of 6.92, artificially contaminated with E. coli O157:H7 and Total coliform colonies. The results indicated that ozonation time was the most critical factor in bacterial inactivation, with significant reductions observed beyond 105 seconds at ORP values of 725 mV or higher, achieving complete inactivation of both E. coli and Total coliform. ANOVA revealed that time and its quadratic term had a statistically significant effect, although the lack of model fit suggests that additional variables may influence the disinfection process. Optimization using Design-Expert software identified 719 mV and 110 seconds as the ideal ORP and ozonation time, respectively, achieving 0 MPN/100 ml for both bacterial groups. These findings provide a robust technical foundation for enhancing water purification systems using automated ozone-based technologies, contributing to safer, more efficient, and sustainable solutions for microbiological treatment of drinking water.