Backwashable media bed filtration system and drop in retrofit kit for same

A retrofit kit for a backwashable granular media bed filtration system, the kit comprising a cylindrical backwash filter screen having an annular cross section, an upstream side corresponding to an outer surface, and a downstream side corresponding to an inner surface, wherein the backwash filter screen comprises, in series from the upstream side to the downstream side:

• (a) a first profile wire assembly comprising:
• [1] multiple, spaced apart, parallel lengths of a first profile wire formed into a cylinder, each first profile wire having an upstream edge and a downstream edge, wherein the upstream edges of the multiple, spaced apart, parallel lengths of the first profile wires and spaces therebetween define an upstream side of the first profile wire assembly, wherein the upstream side of the first profile wire assembly has a total area;
• [2] a first profile wire cross sectional shape which decreases in width in a downstream direction from the upstream edge of the first profile wire, wherein the upstream edge is wider than the downstream edge;
• [3] a slot width between adjacent parallel lengths of first profile wire at the upstream edges of the first profile wires of from 0.007 inches to 0.013 inches;
• and
• [4] a width of the upstream edge of each first profile wire which provides a total slot area of from 20% to 30% of the total area of the upstream side of the first profile wire assembly;
• (b) a first support rod assembly attached to a downstream side of the first profile wire assembly and comprising multiple, spaced apart, parallel lengths of a first support rod formed into a cylinder, each first support rod oriented substantially orthogonal to the lengths of first profile wire, wherein each first support rod has an upstream edge and a downstream edge, and wherein the upstream edges of the first support rods and spaces therebetween define an upstream side of the first support rod assembly;
• and
• (c) a first stiffening rod assembly attached to a downstream side of the first support rod assembly and comprising multiple, spaced apart, parallel lengths of a first stiffening rod formed into a cylinder, each first stiffening rod oriented substantially orthogonal to the lengths of first support rod, wherein each first stiffening rod has an upstream edge and a downstream edge, and wherein the upstream edges of the first stiffening rods and spaces therebetween define an upstream side of the first stiffening rod assembly;
• wherein the upstream edge of each first profile wire and spaces therebetween, each first support rod, and each first stiffening rod corresponds to the edge closer to the outer surface of the cylindrical backwash filter screen, while the downstream edge of each first profile wire and spaces therebetween, each first support rod, and each first stiffening rod corresponds to the edge closer to the inner surface of the cylindrical backwash filter screen;
• and
• wherein the upstream side of the first profile wire assembly, the first support rod assembly, and the first stiffening rod assembly corresponds to the side closer to the outer surface of the cylindrical backwash filter screen, while the downstream side of the first profile wire assembly, the first support rod assembly, and the first stiffening rod assembly corresponds to the side closer to the inner surface of the cylindrical backwash filter screen.