To explore the treatment method that enables the quality of ballast water to meet the discharge standard

the O3/UV combined ballast water treatment system was established

in which O3 and UV can be controlled independently. Escherichia coli and Dunaliellasalina are target microorganisms. To study the system performance in inactivating microorganisms

MPN and CFDA-AM fluorescence staining were used to count residual viable bacteria and residual viable algae respectively. N

N-Diethyl-p-phenylenediamine (DPD) spectrophotometry was used to measure the attenuation of total residual oxide (TRO) generated in the system. The results show that O3 and UV have a synergistic effect

and the combination of the two has better performance of inactivation than that of the individual treatment. Under the condition of 67 μW/cm2 UV irradiance

1.62 g/h of the O3 dosage for 1s exposure

the Escherichia coli and Dunaliellasalinacan cannot be detected after 2 h

which means the effluent can meet IMO microbial inactivation standards. TRO concentration decayed with time

and the experiment did not detect the resurrection of bacteria and algae

which indicate a good continuous inactivation performance of the system. Compared with individual treatment

the combined system increases the treatment efficiency and reduces the energy consumption

which makes itself a promising method.