Patent ID: 6120689
Filing Date: 2000-09-19
Classification: B01D,C02F

Abstract:
A method for producing high purity product water using a three pass reverse osmosis system, the method having the ability to produce water having a resistivity in the range of 10 to 18 megohm-cm, the method comprising the steps of:(a) providing a feedwater to be purified, said feedwater having a basic pH;(b) introducing the feedwater to a high pressure side of a first reverse osmosis membrane module comprising a non-charged membrane;(c) passing water through said first reverse osmosis membrane to provide a first retentate and a first permeate, said first permeate maintained at a basic pH;(d) transferring said first permeate to a high pressure side of a second reverse osmosis membrane module comprising a non-charged membrane;(e) further purifying said first permeate by passing at least a portion thereof through said second reverse osmosis membrane to provide a second retentate and a second permeate having a pH of less than 6.2 and resistivity in the range of 0.5 to 2.5 megohm-cm;(f) adjusting said second permeate to a pH in the range of 6.2 to 8.5 to provide an adjusted second permeate;(g) providing a third pass reverse osmosis module having a third high pressure side and a third low pressure side, said third pass reverse osmosis module comprising a third pass reverse osmosis membrane selected from a positively charged membrane and a negatively charged membrane;(h) introducing said adjusted second permeate to the high pressure side of said third pass reverse osmosis module; and(i) passing at least a portion of said adjusted second permeate through said third pass reverse osmosis membrane to permeate high purity product water having a pH in the range of 6.8 to 7.2.