Patent ID: 6258278
Filing Date: 2001-07-10
Classification: B01D,C02F,Y10S

Abstract:
A method of producing high purity water using dealkalization and reverse osmosis membrane systems having enhanced membrane life, the method comprising:(a) providing a body of feedwater to be purified;(b) adding a coagulant to said body to form a floc concentration in the range of 2 to 6 gm/l in a size range of 0.2 to 10 .mu.m in said body for adsorbing contaminants thereon;(c) removing a portion of said body through a submerged semi-permeable membrane to provide a purified feedwater;(d) treating said purified feedwater with a strong base anion exchange for purposes of dealkalization to remove ions including bicarbonate, carbonate, sulfate and nitrate ions to provide a substantially completely dealkalized water containing ions having a major portion thereof comprised of sodium and chloride ions;(e) removing carbon dioxide from said dealkalized water to provide dealkalized, decarbonated water substantially free of carbon dioxide;(f) maintaining said decarbonated water at a pH in the range of 6 to 7.7;(g) providing a first membrane module having a first high pressure side and a first low pressure side separated by a first membrane;(h) introducing said dealkalized, decarbonated water to the first high pressure side of said first membrane and producing a first permeate in said first low pressure side to provide a permeate having a pH in the range of about 6.5 to 7.5;(i) providing a second membrane module having a second high pressure side and a second low pressure side separated by a second membrane; and(j) introducing said first permeate to the high pressure side of said second membrane module and passing water through said second membrane producing said high purity water having a resistivity greater than 0.8 microhm-cm in the low pressure side of said second membrane.