Escherichia coli inactivation by pressurized CO2 treatment methods at room temperature: Critical issues

This study aims to increase the inactivation efficiency of CO₂ against Escherichia coli under mild conditions to facilitate the application of pressurized CO₂ technology in water disinfection. Based on an aerating-cycling apparatus, three different treatment methods (continuous aeration, continuous reflux, and simultaneous aeration and reflux) were compared for the same temperature, pressure (0.3–0.7 MPa), initial concentration, and exposure time (25 min). The simultaneous aeration and reflux treatment (combined method) was shown to be the best method under optimum conditions, which were determined to be 0.7 MPa, room temperature, and an exposure time of 10 min. This treatment achieved 5.1-log reduction after 25 min of treatment at the pressure of 0.3 MPa and 5.73-log reduction after 10 min at 0.7 MPa. Log reductions of 4.4 and 5.0 occurred at the end of continuous aeration and continuous reflux treatments at 0.7 MPa, respectively. Scanning electron microscopy (SEM) images suggested that cells were ruptured after the simultaneous aeration and reflux treatment and the continuous reflux treatment. The increase of the solubilization rate of CO₂ due to intense hydraulic conditions led to a rapid inactivation effect. It was found that the reduction of intracellular pH caused by CO₂ led to a more lethal bactericidal effect.