Abstract: A ballast water treatment plant, as well as a method of operation, configured for treating water to be delivered into a ballast tank is disclosed. The system and method is configured for, during ballast offload operation and by means of a first backwashing water conduit, lead backwashing water from a ballast water filter to a suction side of a ballast water pump. This way, filter backwashing water is circulated through the ballast water pump and the ballast water filter.