Patent ID: 6090284
Filing Date: 2000-07-18
Classification: B01D

Abstract:
An underdrain unit in a granular filtration system having a bed of granular material positioned over a tank floor and through which liquid is filtered to pass toward a tank outlet below the underdrain unit, and wherein a backflushing system is provided for backflushing the granular filter by liquid and gas scouring, comprising:perforated underdrain structure adjacent to the tank floor and covering an outlet drain area of the tank floor and defining an interior space downstream of the perforations for outflow of filtrate by gravity, the underdrain structure being positioned to support a granular medium comprising a bed of granular filtering material, and the underdrain structure defining generally an undulating shape over the tank floor with parallel, repeated convex longitudinal portions between which are elongated troughs,retention structure retaining the perforated underdrain structure to the tank floor, comprising tubular structural members extending longitudinally, in the troughs of the undulating underdrain structure, and each tubular member having gas exit perforations at spaced locations along its length,anchor means securing the tubular member to the tank floor and tightened so as to engage the tubular member against the underdrain structure within said trough and to hold the underdrain structure securely against the tank floor, anda gas delivery system including pressurized gas conduits connected to the tubular members for delivering pressurized gas to the tubular members for gas scouring of the granular medium during backflushing of the medium.