Patent ID: 7919001

Claim:
A method for purifying water, comprising the steps of: separating a supply stream into an RO permeate stream and an RO reject stream with a reverse osmosis unit; providing the RO reject stream to a nanofiltration membrane; removing non-monovalent salt impurities from the RO reject stream with said nanofiltration membrane unit to produce a treated stream; providing the treated stream to a concentrating compartment of an electrodeionization unit; outputting a concentrate effluent stream from said concentrating compartment; providing a diluting feed stream to a diluting compartment of said electrodeionization unit, feeding said RO permeate stream to said diluting feed stream; and, producing an EDI product stream of purified water with said electrodeionization unit, said method producing said EDI product stream without using a recycle pump for recycling the concentrate effluent stream back to said concentrating compartment or said reverse osmosis unit.