Inactivation of Legionella in aqueous media by high-pressure carbon dioxide

This work aimed to investigate the inactivation of Legionella in aqueous media using high-pressure carbon dioxide (HPCD). Both discontinuous and continuous operations were tested. During batch treatments, the increased pressure improved the inactivation of Legionella, probably due to better dispersion and dissolution of the HPCD in the aqueous medium. Inactivation also increased with temperature. After 10 min and 26 °C it was not necessary to exceed 20 MPa, where reductions higher than 4.2 log were reached. At 10 MPa, reductions higher than 3.1 log were reached, good enough for real aqueous environments, which rarely exceed 102 CFU mL−1. Total inactivation was reached at 38 °C at all pressures. For a given temperature, treatment with HPCD was always much more effective than thermal treatment. During continuous treatments, a contact time of 1 min at 28 °C and 10 MPa were enough for the total inactivation of Legionella in co-current flow with a CO2/suspension mass ratio of 1. Simulation with Aspen Plus® revealed that depressurization of the sterile water to remove gaseous CO2 cooled it sufficiently to be used as a cooling service.