Patent ID: 6899812

Claim:
A process for treating water containing solids to produce a permeate lean in solids comprising: (a) providing a filter for treating water containing solids to produce a permeate lean in solids comprising: (i) an open tank defining a generally horizontal flow path between an inlet to supply a feed water containing solids into the tank and an outlet for water rich in solids to leave the tank; (ii) six or more membrane modules of filtering membranes placed in the tank spaced horizontally consecutively along the flow path, such that (A) any distance between adjacent membrane modules along the flow path is less than one half of the length of a membrane module measured along the flow path. (B) the total length of all of the membrane modules measured along the flow path excluding any distance between them along the flow path is at least twice the width of the membrane modules measured perpendicular to the flow path and (C) the distance from the membrane modules to the walls of the tank measured perpendicular to the flow path is greater than any distance along the flow path between adjacent membrane modules; (iii) permeate collectors for connecting a permeate side of the filtering membranes to a source of negative pressure; and, (iv) agitators below the modules operable when the tank is filled with water containing solids to entrain water containing solids around the membrane modules and flow the water containing solids upwards through the modules substantially throughout permeation; (b) introducing a feed water containing an initial concentration of solids into the tank through the inlet to immerse the membranes in water containing solids; (c) producing a filtered permeate with a reduced concentration of solids on a permeate side of the membranes by applying a negative pressure to the permeate collectors; (d) removing the permeate produced on the permeate side of the membranes from the tank; (e) withdrawing a retentate having an increased concentration of solids compared to the initial concentration of solids from the tank through the outlet substantially continuously while producing the filtered permeate; (f) introducing feed water into the tank to replace water removed from the tank to keep the membranes immersed in water during the step of producing the filtered permeate; and, (g) operating the agitators to create a localized flow of tank water about each module substantially throughout permeation in which water in the tank flows upwards through the membrane module then downwards and towards the outlet in a space beside the membrane module.