A combination type ballast water treating system is provided to easily remove harmful underwater organisms contained in ballast water, thereby preventing environmental pollution due to discharge of the ballast water. A main body(230) has a filtering unit(110) for filtering ballast water, a cleaning unit(120) for cleaning the filtering unit using the ballast water, an inflow tube, and an outflow tube. A UV treatment unit(130) applies UV to the filtered ballast water. An electrolysis unit(140) electrolyzes the UV-treated ballast water. A controller controls the filtering unit, the cleaning unit, the UV treatment unit, and the electrolysis unit. The controller drives the filtering unit and the cleaning unit alternately and continuously.
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