Conventional liquid cyclone devices tend to break flocs and thus cannot be used for floc separation. Further, there are no ballast water treatment devices that can simultaneously remove plastics and microplastics floating in the sea. In addition, there are no ships or ship operation methods that address the problem of pollution due to plastics and microplastics floating in the sea.
To achieve cyclone separation of a fluid including easily broken flocs, flocs that include a magnetic body are guided by means of centrifugal force and magnetic force to a flow in the vicinity of an outer shell of a cyclone, then to a channel between an inner shell and the outer shell, and discharged from a lower outlet. The inner shell prevents an upward flow from affecting the flocs, making it possible to achieve reliable separation of the flocs.