Novel water softening process using membranes

Claim 1

A process for reducing the hardness of water comprising: (a) contacting water containing hardness ions with a first surface of a water softening membrane at a transmembrane pressure in the range from about 50 to about 100 psi, wherein said membrane is prepared by a process comprising: (i) contacting a crosslinked, aromatic polyamide discriminating layer of a reverse osmosis membrane with an aqueous solution of a compatible strong mineral acid; (ii) maintaining the membrane in contact with the acid at an elevated temperature for a period sufficient to produce a membrane having a water flux of at least about 8 gfd and a MgSO 4 rejection of at least about 65 percent when tested under reverse osmosis conditions at 50 psi and 25° C. using an aqueous solution of 0.2 weight percent MgSO 4 ; and (iii) contacting the membrane from step (ii) with a rejection enhancing agent so as to produce a membrane having a MgSO 4 rejection of at least about 85 percent; and (b) separating a permeate from a second surface of the water softening membrane, wherein the permeate contains a reduced concentration of hardness ions.