The filtration system having a housing having an inlet, at least one outlet being axially spaced from the inlet and forming a helical purge path therebetween, and a filtrate outlet extending out along the axis, with a flow rate ratio being balanced by flow restriction between the filtrate outlet and the at least one purge outlet during regular operation; a filter element including a filtration membrane and a support membrane mounted concentrically around the axis, at least one of said filtration membrane and support membrane being rotatably mounted to the housing for rotation about the axis to impart a relative rotation speed between the filtration membrane and support membrane during operation; the system being operable to temporarily increase the flow rate ratio through the at least one outlet compared to said regular operation.

A ballast water treatment device includes a filtration device and an irradiation device that irradiates, with ultraviolet rays, filtered water that has been filtered. The filtration device is a device that removes 99.999% or more of L-size organisms having a minimum part size of 50 μm or more, and 90% or more of S-size organisms having a minimum part size of 10 μm or more and less than 50 μm. The irradiation device is capable of sterilizing the filtered water at a flow rate of 250 m.sup.3/h and a power consumption of 13 kW to eliminate 90% of S-size organisms immediately after a sterilization treatment.

This invention relates to a filter which is especially for filtering microfibres which can, for example, originate from the washing of textiles. The filter is rotatable around an axis of rotation. The filter provides good filtering efficiency and improved resistance to blocking.

A centrifugal filter unit for an apparatus, wherein the apparatus is for use in the treatment of a substrate with a treatment formulation, the centrifugal filter unit comprising; a) a housing having an outlet configured to allow a filtrate to exit the centrifugal filter unit; b) a filter rotatably mounted in the housing, wherein the filter comprises a first end proximate a first end of the housing, a second end proximate a second end of the housing and a side wall connecting the first end of the filter and the second end of the filter, wherein the first end, second end and side wall of the filter define a filter chamber, and wherein the side wall comprises perforations configured to allow liquid to pass throughout to prevent solid material from passing through; c) a lid configured to substantially seal the first end of the housing; d) an inlet configured to allow a feed to enter the filter chamber; e) a cap at the first end of the filter, wherein the cap comprises an aperture that cooperates with the inlet to allow the feed to enter the filter chamber; f) a drive means for rotating the filter; and g) an impeller, wherein the impeller is comprised in the filter chamber; wherein the centrifugal filter unit is configured such that when the impeller rotates, the feed is drawn in to the filter chamber through the inlet and liquid is expelled through the perforations.

A centrifugal filter unit for an apparatus for use in the treatment of a substrate with a treatment formulation is provided. The centrifugal filter unit includes a) a housing having an outlet; b) an inlet; c) a filter rotatably mounted in the housing and having a side wall with perforations that allow liquid to pass through but prevent solid material from passing through; d) an aperture; and e) a drive for rotating the filter. A portion of the centrifugal filter unit in the filter chamber is removable and, when removed from the centrifugal filter unit following operation, takes with it at least a portion of the solid material prevented from passing through the perforations. The centrifugal filter unit is arranged such that the feed is drawn into the filter from the inlet through the aperture and the liquid is expelled through the perforations to the outlet and the solid material is retained in the filter. The removable portion is shaped to scrape against the side wall during removal.