Provided is a ballast water treatment device with which filter clogging can be effectively eliminated by backwash using a simple configuration. The ballast water treatment device is provided with: a filter 52; an introduction line L1; a line L11through which the ballast water W2 filtered by the filter 52 flows; a flow rate adjustment unit (valve V12) for adjusting the flow rate of the ballast water W2 that flows through the line L11; and a flow rate control unit (control unit 9) for controlling the flow rate adjustment unit V12. The flow rate control unit 9, in a situation where the filtering capability of the filter 52 is decreased, controls the flow rate adjustment unit V12 so as to increase the pressure on a secondary side of the filter 52 by decreasing the flow rate of the ballast water W2, and the filter 52 is then subjected to backwash with the pressure on the secondary side of the filter 52 having been increased.

A system for cleaning and sterilizing a water flow comprises a main treatment line with a pump to pump water from a water storage, a main filter, a sterilizing station and a system outlet. The main filter is provided with a first filter element and a backflush member to rinse the first filter element with backflush water. The secondary treatment line connects to an outlet of the backflush member, and has a backflush filter to remove silt from the backflush water. The main filter is designed such that the pressure difference over the, first filter element is at least 0.1 bar (10 kPa) and the backflush filter is designed such that the pressure difference over the backflush filter element is less than 0.05 bar (5 kPa).

A fish pond filtration device includes a filter tank, a conical filter cylinder, a garbage collection trough, and a sewage pipe; the conical filter cylinder, the garbage collection trough and the sewage pipe are located in the filter tank; water discharge ports are provided in a bottom or a side wall of the filter tank, and the conical filter cylinder is in rotary fit with the filter tank; the garbage collection trough is disposed below a large-diameter end of the conical filter cylinder, a filter port and a sewage discharge port are provided in a bottom of the garbage collection trough, and the sewage discharge port communicates into a sedimentation barrel; and a water pump is disposed at one end of the sewage pipe, the water pump is located in a fish pond, and the other end of the sewage pipe extends into the conical filter cylinder.

A strainer includes a housing having an inlet port, an outlet port, and a flow path from the inlet port to the outlet port. A strainer drum is supported for rotation in the housing. The drum has an open end arranged in the flow path to receive water flowing from the inlet port into the drum through the open end, and has a porous side wall arranged in the flow path to strain solids from water flowing outward from the drum through the porous side wall. A backwash tube has a backwash inlet located inside the drum and facing outward of the drum beside an inner surface of the porous side wall.

A suction device for a disc filter includes at least one suction bar per discoid filter body and a suction slit designed for suctioning the impurities of the filter cloth, as well as a suction pump for suctioning the impurities. The suction bar is movable radially from the axis of rotation of the disc filter.