Disinfection effect of pressurized carbon dioxide on Escherichia coli and Enterococcus sp. in seawater

Abstract

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.

<i>Escherichia coli</i> Inactivation Using Pressurized Carbon Dioxide as an Innovative Method for Water Disinfection

“…The disinfection efficiency of pressurized CO 2 substantially increased with increasing temperatures (11-28°C) at 0.7 MPa (Figure 7). The E. coli load was reduced by more than 5.0 log within 25 min of treatment at 11°C, whereas only 20, 12, and 10 min of pressurized CO 2 treatment at 15, 18, and 20-28°C, respectively, were required to reduce the E. coli load to a similar extent [23]. Taken together, these findings suggest that E. coli inactivation by pressurized CO 2 could be efficiently conducted at low-pressure (0.7 MPa) and ambient temperature Figure 6.…”

“…However, the increased pressure application from 0.7 to 0.9 MPa did not result in significant increase in the rate of bacterial inactivation. These data indicated that the optimal CO 2 pressure for inactivating E. coli was in the range of 0.7-0.9 MPa, and hence, 0.7 MPa was chosen as the optimal pressure condition for effective bactericidal activity [23].…”

“…The pump was used to apply 0.12 MPa higher pressure than that inside the main chamber. The sensitivity of bacteria to pressurized CO 2 treatments under different conditions was determined by varying the CO 2 pressure (0.2-0.9 MPa) and seawater temperature (11-28°C) for a 25-min treatment period [23]. Each experiment was conducted in triplicate.…”

“…The prepared cells were then soaked in t-butyl alcohol two times for 1 h, freeze-dried for 2 h, and sputter coated with gold-palladium. Finally, the cells were examined by using a scanning electron microscope (QuantaTM 3D, FEI Co., USA) at 20 kV [23].…”

“…However, the pressure (10 MPa) and temperature (35-55°C) requirements for effective inactivation [16,17] are still high from a practical standpoint. Our research group has developed a novel method that uses low-pressure CO 2 treatments (0.2-1.0 MPa) based on technology that produces high amounts of dissolved gas in water to inactive bacteria and bacteriophages in freshwater [19][20][21] and seawater [23,24]. Cheng et al [19] suggested that the sudden discharge and resulting reduction of pressure could cause cells to rupture via a mechanical mechanism, and further, that this would be lethal to cells at high levels of dissolved CO 2 at 0.3-0.6 MPa and room temperature.…”