System for maintaining a clean skein of hollow fibers while filtering suspended solids

In a method for maintaining production of permeate at equilibrium flux, in a skein submerged in a solids-containing substrate held in a tank, continuously, by scrubbing hollow fiber membranes ("fibers") of said skein with bubbles generated from scrubbing gas flowed into an aerator, the improvement comprising,

• supplying said scrubbing gas to said aerator's air plenum at a pressure greater than the liquid head between the surface of substrate in the tank and the surface of the substrate in the plenum;
• maintaining a substantially uniform flow of a stream of said bubbles through each of plural orifices in lateral walls of said aerator, in which stream the majority are coarse bubbles having an effective diameter in excess of 3 mm and rise at a velocity in the range from about 5 ft/sec to 10 ft/sec (1.5 m/sec to 3 m/sec);
• periodically returning permeate to said aerator through a conduit means connected thereto;
• injecting a desired amount of said flushing gas into said permeate in said conduit means within an injection period of less than 10 min so as to flush said aerator with a two-phase mixture of flushing gas and permeate flowing laterally through said aerator, in a volumetric ratio of flushing gas:permeate in the range from about 1:2 to about 25:1, said gas in said mixture being at elevated pressure, above that of permeate flowing in said permeate line, and in addition, sufficient to overcome a hydrostatic head above said aerator, so as to provide discrete dispersed masses of permeate which impinge against internal walls of said aerator;
• maintaining flow of said two-phase mixture for less than 10 min;
• and, returning loosened solid deposits from within said aerator into said substrate;
• and, re-establishing flow of said scrubbing gas.