725-734In this study, the effects of hydroxyl radicals on harmful microalgae in ballast water were investigated experimentally. Using an improvised ballast water treatment system, large concentrations of ·OH were produced and subsequently dissolved in ballast waters of different salinities which are high salinity seawater (HS) and low salinity seawater (LS) in order to eliminate the microalgae. The results show that the outcome of the treatment system fully meets the requirements of G8. At total residual oxidant (TRO) concentrations of 0.41 mg/L and 0.93 mg/L, the maximum concentration of killed algae was observed as 0.5×103 cells/mL and 1×104 cells/mL, respectively. Furthermore, the ·OH efficiently decomposed most organic matter, resulting in an improvement of the ship’s ballast water quality. These results conform to the D-2 ballast water discharge standard of IMO and validate the ·OH as an effective, rapid way of killing algae in the course of conveying the ship’s ballast water
