Ro membrane cleaning method

Direct-osmosis (DO) method for cleaning a semi-permeable membrane in a reverse osmosis RO separation module, said membrane having a feed side with foulant located thereon and an opposite permeate side, a normal RO separation process in the same module including

• feeding by a feed pump, under gauge pressure PGr, raw saline solution comprising solvent and dissolved salts and having osmotic pressure POr to said membrane feed side;
• collecting permeate having osmotic pressure POp from said permeate side, under gauge pressure PGp;
• and
• removing residual brine from said membrane feed side,
• the RO separation being driven by a positive net driving pressure defined by the balance of the pressures PGr, POr, Pop and PGp;
• wherein said direct osmosis method of membrane cleaning comprises feeding to said feed side of the membrane, for a predetermined injection time, without stopping the feed pump, super saline solution (SSS) having an osmotic pressure POs>POr chosen such that the net driving pressure becomes negative, whereby there is provided a backward flow of permeate towards the feed side so as to lift said foulant from said feed side.