Cleaning membrane filter systems - using periodic injection of air on high pressure side with subsequent froth separator

Process for membrane filtration allows injection of a gas into the feed liq. stream to the membrane. The liq. stream leaving the unit passes through a pressure reducing valve and then flows on into a froth sepn. system. Any solids or other debris adheres tothe bubble surfaces and as these expand, it rises to the surface. The froth contg. oil and solids, is skimmed off and fed away. Surface active agents can be added to the liq. feed to improve the sepn. Used esp. for purifying the oily effluent stream from a metal prepn. process or other ultrafiltration or reverse osmosis processes where the feed stream contains dust, sand, carbon, metal splinters and other dirt. Prevents accumulation of such material on the membrane surface allowing prolonged use of the unit.