Comparison of disinfection effect of pressurized gases of CO2, N2O, and N2 on Escherichia coli

• Inactivation performance of CO2 against Escherichia coli is more effective than N2 and N2O.
• Inactivation mechanism is explained via the different properties of N2, N2O and CO2.
• pH reduction caused by CO2 make it most effective to inhibit E. coli in water.
• Optimum conditions of pressure, initial concentration of E. coli are reported.
• Cells under UV-absorbance and SEM images after CO2 treatment confirm E. coli deaths.

Based on the production of gas bubbles with the support of a liquid film-forming apparatus, a device inducing contact between gas and water was used to inactivate pathogens for water disinfection. In this study, the inactivation effect of CO2 against Escherichia coli was investigated and compared with the effects of N2O and N2 under the same pressure (0.3–0.9 MPa), initial concentration, and temperature. The optimum conditions were found to be 0.7 MPa and an exposure time of 25 min. Under identical treatment conditions, a greater than 5.0-log reduction in E. coli was achieved by CO2, while 3.3 log and 2.4 log reductions were observed when N2O and N2 were used, respectively. Observation under scanning electron microscopy and measurement of bacterial cell substances by UV-absorbance revealed greater cell rupture of E. coli following treatment with CO2 than when treatment was conducted using N2O, N2 and untreated water. The physical effects of the pump, acidified characteristics and the release of intracellular substances caused by CO2 were bactericidal mechanism of this process. Overall, the results of this study indicate that CO2 has the disinfection potential without undesired by-product forming.

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