Simultaneous production of multiple grades of purified water by reverse osmosis

A process for simultaneously separately producing high quality product water and lower quality product water by reverse osmosis treatment of impure water under elevated pressure in a unitary elongated pressure resistant container housing at least two semipermeable membrane cartridges arranged in end-to-end relationship, and having an impure feed water inlet near one end and a brine outlet near the other of its ends;

• which comprises:
• a. flowing said impure feed water sequentially in a single stage through the said semipermeable membrane cartridges so that the unpermeated feed water from each cartridge constitutes the feed water for the next cartridge in the sequence;
• b. separately collecting and releasing high quality low total dissolved solids content product water as permeate from at least one of the said semipermeable membrane cartridges nearest the feed water inlet of said pressure resistant container;
• and
• c. separately collecting and releasing lower quality higher total dissolved solids content product water as permeate from the remainder of said semipermeable membrane cartridges in said pressure resistant container.

A multi-stage reverse osmosis process for simultaneously producing an amount of high grade product water and an amount of lower quality product water from a saline feed solution containing from 28,000 to 40,000 ppm TDS comprising:

• a. in an initial stage reducing the salinity of the said feed solution by reverse osmosis to produce an intermediate permeate containing from one-fourth to one-half the salt content of the original feed solution employing an operating pressure of between about 300 and about 500 psi and a semipermeable membrane characterized by a salt rejection of between 40 and 70 percent when tested at 100 psi using a 1,000 ppm NaCl feed solution;
• b. in a subsequent stage reducing the salinity of said intermediate permeate from said initial stage in a unitary, elongated pressure resistant container housing at least two semipermeable membrane cartridges in end-to-end relationship, employing an operating pressure of between about 300 and about 500 psi and semipermeable membranes characterized by a salt rejection of more than 90% when tested at 100 psi using a 1,000 ppm NaCl feed solution by flowing said intermediate permeate sequentially through said cartridges, the unpermeated feed water from each cartridge constituting the feed water from the next cartridge in the sequence;
• c. separately collecting and releasing high quality product water as permeate from at least one of the said subsequent stage semipermeable membrane cartridge nearest the intermediate permeate feed inlet of said pressure resistant container;
• and
• d. separately collecting and releasing lower quality product water as permeate from the remainder of said subsequent stage semipermeable membrane cartridges in said pressure resistant container.