Semicontinuous and batch ozonation combined with peroxymonosulfate for inactivation of microalgae in ballast water

The Ballast Water Management Convention (BWMC) establishes limits regarding the permissible number of viable organisms in discharged ballast water. Ozone as a ballast water treatment is interesting because it can be generated in-situ and has strong oxidant power. Additionally, some oxidants can be formed in reaction with seawater, especially brominated compounds, that assist in inactivating microorganisms. The objective of this study is to assess the efficacy of semicontinuous and batch ozonation as well as their combination with peroxymonosulfate salt (PMS) as methods to be used to ensure compliance with regulation D2 of the BWMC using Tetraselmis suecica as a standard microorganism. Growth modeling method was employed to determine the inactivation achieved by the treatments. The results show that ozone is an effective treatment for accomplishing the D2 of the BWMC. Batch ozonation is more efficient than semicontinuous ozonation probably because of the brominated compounds formed during the ozone saturation of the water. The oxidants that are developed during the ozonation of seawater prolong the residual effect of the treatment throughout the days of storage with practically no presence of them in the ballast tanks at 72 h. The addition of the PMS increases the inactivation in the semicontinuous ozonation, but a threshold concentration of ozone is needed to observe the synergistic effect of both oxidants. No increase is associated with the combination of O₃ and PMS in the case of batch ozonation.