Variable volume filter or concentrator

A method of concentrating the solids of a liquid suspension, comprising the steps of:

• (i) applying the liquid suspension to the outer surface of elastic, microporous, hollow fibers enclosed by a deformable, variable volume diaphragm within a shell to concentrate said solids by
• (a) passing some of the liquid suspension through the walls of the fibers to be drawn off as clarified liquid from the fiber lumens,
• (b) retaining at least some of the solids on or in the fibers or otherwise within the shell with the non-retained solids being removed from the shell with the remainder of liquid,
• (ii) discharging the retained solids from the shell by:
• (a) applying to the fiber lumens a gas at a pressure sufficient to stretch all of the pores, followed by:
• (b) maintaining the flow of the gas at said pressure through the lumens for a time sufficient to drive the liquid from the pores having a bubble point below the pressure of the gas so as to wash out any solids retained in those pores and to subtantially dislodge solids retained on the outer surface of the fibers so that the washed and dislodged solids are removed from the shell to an external collection point, and then,
• (c) reducing the pressure of the gas so that the pores will substantially return to their original size whereupon the gas is removed so that a portion of the liquid suspension passes through the walls of the fiber to be drawn off as clarifying liquid from the fiber lumens;
• and
• (iii) varying the volume of the diaphragm so as to provide a reduced but variable volume during the application of the liquid suspension and a larger volume whilst the pressurized gas is applied.