Photocatalytic inactivation of microalgae: efficacy and cell damage evaluation by growth curves modeling

Abstract

Ballast water in ocean transportation is an important vector for species transferring between areas not connected naturally. Ultraviolet irradiation is a common treatment to inactivate organisms in ballast water. A primary disadvantage inherent to ultraviolet treatment is photoreactivation. This study evaluates the possibility to enhance the efficacy of ultraviolet disinfection with the addition of TiO2 photocatalysis by using the microalga Tisochrysis lutea as an indicator organism. The culture was treated with different ultraviolet doses using a tubular flow-through UV-C reactor equipped with a glass cylinder coated with fixed TiO2. To study the influence of the photoreactivation, an aliquot from every sample was exposed to light immediately after the treatment and another aliquot was kept in the dark for 5 days and subsequently exposed to light. The growth curves were modeled and disinfection kinetics parameters were consequently obtained in order to compare the photocatalytic and ultraviolet disinfection. Results indicated an increase in the disinfection rate by a factor of 4.18 using the photocatalytic reactor, in comparison with the UV-only treatment, in samples exposed to light immediately after the treatment. On the other hand, the disinfection rate was increased, but not significantly, in samples stored in dark after irradiation using the photocatalytic reactor. Data also showed the high extent of photoreactivation, which was reduced by the photocatalytic treatment.