Ultraviolet radiation as a ballast water treatment strategy: Inactivation of phytoplankton measured with flow cytometry

Olsen, Ranveig Ottoey; Hoffmann, Friederike; Hess-Erga, Ole-Kristian; Larsen, Aud; Thuestad, Gunnar; Hoell, Ingunn Alne

Ultraviolet radiation as a ballast water treatment strategy: Inactivation of phytoplankton measured with flow cytometry

2016

This study investigates different UV doses (mJ/cm2) and the effect of dark incubation on the survival of the algae Tetraselmis suecica, to simulate ballast water treatment and subsequent transport.Samples were UV irradiated and analyzed by flow cytometry and standard culturing methods. Doses of ≥400mJ/cm2 rendered inactivation after 1day as measured by all analytical methods, and are recommended for ballast water treatment if immediate impairment is required. Irradiation with lower UV doses (100–200mJ/cm2) gave considerable differences of inactivation between experiments and analytical methods. Nevertheless, inactivation increased with increasing doses and incubation time. We argue that UV doses ≥100mJ/cm2 and ≤200mJ/cm2 can be sufficient if the water is treated at intake and left in dark ballast tanks. The variable results demonstrate the challenge of giving unambiguous recommendations on duration of dark incubation needed for inactivation when algae are treated with low UV doses.

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