Effects of pressure and pressure cycling on disinfection of Enterococcus sp. in seawater using pressurized carbon dioxide with different content rates

ABSTRACT

Interest is growing in a disinfection technique for water treatment without disinfection byproducts. This study presents the result of using a liquid-film-forming apparatus at less than 1.0 MPa for disinfection of seawater. The sensitivity of Enterococcus sp. (ATCC 202155) to the pressurized carbon dioxide (CO₂) was examined under various conditions of pressure cycling, pressure, working volume ratio (WVR), and CO₂ content rate. The key influences on frequency and magnitude of pressure cycling in enhancing Enterococcus sp. inactivation are elucidated. The results reveal strong correlation between pressure cycling and inactivation efficiency (P-value < 0.001). The outcome of linear regression model analysis suggests that the model can explain 93%, 85%, and 89% of the inactivation efficiency of (25% CO₂ + 75% N₂), (50% CO₂ + 50% N₂), and 100% CO₂, respectively. The predicted value was fit with experimental results (p-value <0.05). Under identical treatment conditions (pressure = 0.9 MPa, ΔP = 0.14 MPa, 70% WVR, and 20 ± 1°C), treatment with pressurized CO₂ (100% purity) resulted in complete inactivation 5.2 log of Enterococcus sp. after 70 cycles within 20 min. The Enterococcus sp. inactivation of pressurized CO₂ followed first-order reaction kinetics. The smallest D-value (largest k-value) was induced by pressurized CO₂ (100% purity) at 0.9 MPa, which was obtained at 3.85 min (0.5988 min⁻¹, R² ≥ 0.95). The findings could provide an effective method for enhanced bactericidal performance of pressurized CO₂, to address recently emerging problems in water disinfection.

KEYWORDS:

• Bactericidal performance
• Enterococcus sp.
• inactivation effect
• pressurized CO₂
• pressure cycling
• water disinfection

Acknowledgments

This study was supported by a cooperation agreement between Yamaguchi University (Japan) and the Ministry of Education & Training of Vietnam.

Funding

The authors would like to thank the Takahashi Industrial and Economic Research Foundation for financial support.