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Abstract

A process for purifying water including removing cations, anions and carbon dioxide and/or ammonia from water feed stream to produce high purity water having a resistivity of greater than 1 megohm-era comprising the steps of providing a water feed stream to be purified, the stream containing cations, anions and carbon dioxide and/or ammonia; introducing the water feed stream to a high pressure side of a first reverse osmosis membrane module; passing water through the first reverse osmosis membrane to provide a first retentate having cations and anions concentrated therein and a first permeate depleted in cations and anions and containing carbon dioxide and/or ammonia; adding the first permeate to a high pressure side, of a gas permeable hydrophobic membrane module; passing carbon dioxide and/or ammonia through the gas-permeable membrane from the first permeate in the high pressure side of the gas-permeable hydrophobic membrane to provide a carbon dioxide and/or ammonia permeate on a low pressure side of the hydrophobic membrane and to provide a carbon dioxide and/or ammonia depleted retentate thereby removing carbon dioxide and/or ammonia from the first permeate; transferring the carbon dioxide and/or ammonia depleted retentate to the high pressure side of a second reverse osmosis membrane; and further purifying the carbon dioxide and/or ammonia depleted retentate by passing at least a portion thereof through the second reverse osmosis membrane to provide a second retentate and a second permeate, the second permeate having low levels of carbon dioxide and/or ammonia and having a resistivity greater than 1 megohm-cm.

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First Claim