Ballast water production method and ballast water treatment system

A ballast water treatment system, comprising:

• a filtering unit having a housing and a filter housed in the housing;
• a raw water passage for supplying raw water to a primary side in the housing of the filtering unit, said primary side being located upstream of the filter in the housing, the raw water passage being provided with a first switching valve and a pump;
• a filtered water passage for sending filtered water produced in the filtering unit from a secondary side in the housing to a ballast tank, the secondary side being located downstream of the filter in the housing, and the filtered water passage being provided with a second switching valve;
• a discharge passage for discharging water from a secondary side of the filtering unit, said secondary side being located downstream of the filter, the discharge passage being provided with a third switching valve;
• a gas passage for supplying gas to the secondary side in the housing of the filtering unit, the gas passage being provided with a fourth switching valve;
• and
• a controller for controlling the first to fourth switching valves,
• wherein the controller is configured to:
• conduct a first control of the first switching valve and the second switching valve to be opened and the third switching valve and the fourth switching valve to be closed, and the pump to be driven to filter the raw water by the filtering unit,
• conduct a second control of the first switching valve and the second switching valve to be closed and the third switching valve and the fourth switching valve to be opened, and the pump to be stopped to rinse the filter,
• control, after the first control and before the second control, the first switching valve, the third switching valve, and the fourth switching valve to be closed and the second switching valve to be opened, and the pump to be stopped, thereby flowing back the filtered water remaining in the filtered water passage into the secondary side in the housing, and
• control, after the first control and before the second control, the first switching valve, the second switching valve, and the third switching valve to be closed and the fourth switching valve to be opened, and the pump to be stopped.