Effect of inlet ozone concentration on the performance of a micro-bubble ozonation system for inactivation of Bacillus subtilis spores

A novel ozonation system based on micro-bubble technique was applied as a disinfection process in this study. The effect of inlet ozone concentration on the disinfection performance was comprehensively investigated. Bacillus subtilis spore was used as a model microorganism to evaluate the disinfection performance. In the micro-bubble ozonation system is operated at the same ozone dosage, the log reduction under high inlet ozone concentration was extremely higher than that under low inlet ozone concentration within 3 min of contact time. When the contact time was 3 min, the log reduction at the inlet ozone concentration of 140 mg/L was 5.2, which was nearly ten times of that at the inlet ozone concentration of 40 mg/L (0.5-log reduction). In addition, the ozone utilization efficiency was also enhanced by increasing the inlet ozone concentration. A decrease in bubble diameter was found under higher inlet ozone concentration and the interfacial area per unit volume of the micro-bubble was significantly higher due to the reduction in bubble diameters. This observation can well explain the increase in mass-transfer coefficient (KLa) and the enhancement in the ozone utilization efficiency. The result of this study showed that raising inlet ozone concentration is a promising method which could enhance the disinfection performance in a micro-bubble ozonation system.