QUERSTROMFILTRATION

The filter has a spiral of, or parallel, spaced lengths of, double-ply material whose plies are seamed together along spaced, longitudinal seams to provide an array of side-by-side tubes. The filter support material is highly flexible and has a thickness not greater than 1 mm. Due to the tubular formation, the filter support has an uninterrupted filter zone of substantial area relative to the total area of the filter support; during filtration (when the filter support is under the pressure of the feed) the tube walls bulge out and the filter zone is restrained solely by tensile forces in the filter support itself. Substantial movement of the filter support is possible in the direction at right angles to its face when the pressures on either side of the filter support are equal. The filter support has many applications, but one application is when the filter is connected downstream of an aeration vessel with no intervening vessel, the concentrate outlet of the filter being connected to the aeration vessel for sludge return.