Evaluation of ozone treatment for bacterial disinfection of ballast water

Abstract

In 2004, the International Maritime Organization (IMO) adopted the International Convention for the Control and Management of Ballast Water and Sediments (BWMC), aiming to mitigate the spread of organisms through ballast water. In this study, ozone has been employed as the oxidizing agent in ballast water, both on its own and in combination with hydrogen peroxide (H2O2) and peroxymonopersulfate (PMS). Disinfection is carried out using a discontinuous method, targeting Vibrio alginolyticus and Enterococcus faecalis. The application of ozone at a concentration of 0.7 mg/L in seawater achieved 4 log-reductions of E. faecalis in less than 4 min. In the case of V. alginolyticus in seawater, the application of 0.6 mg/L of ozone and a contact time of 3 min was sufficient to achieve a reduction of 4 logarithmic units. This highlights the greater resistance of E. faecalis to the treatment compared to V. alginolyticus. In order to achieve the same level of disinfection for E. faecalis, a higher concentration of ozone and longer exposure time are required. Combining ozone with either H2O2 or PMS did not improve treatment. Based on the treatments presented in this study, it would be feasible to treat ballast water with an E. faecalis concentration of up to 3.7·106 CFU/100 mL and a V. alginolyticus concentration of up to 4.25·104 CFU/100 mL and still meet the levels required by BWMC. These concentrations are much higher than those found commonly in the marine environment, so the treatment would reduce the concentrations to levels below the D-2 standard.