Patent ID: 7481930

Claim:
A method of forming a gravel-less polishing filter for filtering water and/or wastewater, said method comprising the steps of: (a) determining at least two parameters for a layer of filter media to be installed directly above a gravel-less underdrain in a polishing filter wherein one of the at least two parameters is an effective size less than 1 mm and the other of the at least two parameters is a uniformity coefficient less than 2; (b) providing a first lot of filter media satisfying said at least two parameters for the layer of filter media to be installed directly above a gravel-less underdrain; (c) providing a second lot of media that does not satisfy at least one of said at least two parameters for the layer of filter media to be installed directly above a gravel-less underdrain; and, (d) blending at least a portion of said first lot of filter media with at least a portion of said second lot of media to form a third lot of media that satisfies both of said at least two parameters for the layer of filter media to be installed directly above a gravel-less underdrain, said third lot of media having a composition such that when installed in a filter at least a portion of the larger particles settle directly on top of the gravel-less underdrain thereby forming a protective barrier preventing smaller particles from clogging the gravel-less underdrain.