DESCRIZIONE
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 through but 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.