Studies on the O₃-initiated disinfection from Gram-positive bacteria Bacillus subtilis in aquatic systems

Abstract

The kinetics of inactivation of Gram-positive strain, Bacillus subtilis in aquatic systems was investigated as function ozone aeration duration under varied conditions. Oxygen flow was in situ enriched with ozone using ozoniser, with [O₃] ranging from (0.3 – 9.8) × 10⁻⁵ moles per liter of oxygen. The inactivation kinetics of B. subtilis followed pseudo–first-order kinetics with respect to microbe, under excess [O₃] conditions. The disinfection kinetics had first order dependence on ozone concentration and the overall second-order rate constant was (7.54 ± 1.37) × 10³ M⁻¹ min⁻¹. The effect initial temperature and pH of the system on the ozone initiated inactivation of microbe was also explored. Relative to hydroxyl radicals, molecular ozone was found more effective in microbial inactivation. Appropriate mechanism for ozone initiated inactivation is proposed. Ozone aeration significantly decreased the BOD levels of natural and B. subtilis spiked waters.

Keywords:

• Bacillus subtilis
• bacteria
• kinetics
• disinfection
• ozone
• pH

Acknowledgments

Authors sincerely thank the National Research Foundation (Pretoria) and the University of KwaZulu-Natal for the financial support, and Prof. J. Lin and Ms. D. Fowlds, School of Microbiology, UKZN for their support.