Ship ballast water should be disinfected before being discharged into the ocean to avoid the dispersal of non-native species into the marine environment. This study presents the results of using pressurized carbon dioxide (CO2) at less than 1.0 MPa for inactivating Escherichia coli and Enterococcus sp. in artificial seawater (3.4% salinity). The bactericidal effects of pressurized CO2 were assessed using a liquid-film-forming apparatus under various conditions of pressure, temperature, and working volume ratio (WVR). Additionally, leakage of proteins and nucleic acids from cells was measured. Cell morphology of untreated cells and cells treated with pressurized CO2 was assessed using scanning electron microscopy (SEM). Pressurized CO2 treatment affected both strains; however, Enterococcus sp. exhibited higher resistance to pressurized CO2 treatment than did E. coli. Under identical treatment conditions (0.7 MPa, 20 °C, and 50% WVR), more than 5.0 log reduction in the load of E. coli and Enterococcus sp. was achieved after treatments for 5 min and 20 min, respectively. Release of intracellular contents occurred during the treatment process and SEM images of E. coli and Enterococcus sp. revealed that morphological changes had occurred after the treatment with pressurized CO2. Hence, pressurized CO2 has potential applications for inactivating pathogens in ballast water.

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