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

Abstract

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 3min of contact time. When the contact time was 3min, the log reduction at the inlet ozone concentration of 140mg/L was 5.2, which was nearly ten times of that at the inlet ozone concentration of 40mg/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.