Patent ID: 6190556
Filing Date: 2001-02-20
Classification: B01D,C02F,Y02A

Abstract:
A method of producing potable water by desalinating an aqueous feed of seawater which contains high concentrations of monovalent and divalent ions comprising the steps of:locating a reverse osmosis element (RO) and a nanofiltration (NF) element for series flow in a single pressure vessel having an inlet and a concentrate outlet;pumping an aqueous feed containing monovalent ions and divalent ions in series flow through the RO and NF elements in said pressure vessel at a pressure which is below seawater's osmotic pressure so that substantially no permeation occurs through said RO element, but which is such that said NF element creates a first concentrate stream and a NF permeate stream having a highly reduced concentration of divalent ions and also a reduced concentration of monovalent ions;collecting and temporarily storing said NF permeate stream in a reservoir; andinterrupting said pumping of said aqueous feed and instead pumping said temporarily stored NF permeate from the reservoir through said pressure vessel inlet at a pressure above said NF permeate's osmotic pressure while blocking permeate flow within said NF element so that said second concentrate stream from said RO element only flushes feed passageways within said NF element while causing permeation to occur through said RO element which creates an RO permeate stream of potable water and a second concentrate stream.