US 5,925,255 A · Method and apparatus for high efficiency reverse osmosis operation

Abstract

A process for treatment of water via membrane separation equipment. Hardness and non-hydroxide alkalinity are removed from feedwaters to very low levels, preferably by simultaneous removal in a weak acid cation ion exchange resin. Then, ionization of sparingly ionizable components in the feedwater is substantially accomplished by increasing the pH of the feedwater preferably up to about pH 10.5, or higher. In this manner, species such as silica become highly ionized, and (a) their rejection by the membrane separation process is significantly increased, and (b) their solubility in the reject stream from the membrane process is significantly increased. Passage of weakly ionized species such as boron, silica, and TOC is reduced by a factor of ten or more. Recovery ratio of ninety percent (90%) or higher is achievable with most brackish feedwaters, while simultaneously achieving a substantial reduction in cleaning frequency. The method is particularly useful for the preparation of high purity water. Although the silica level in the reject water in this process is increased from the conventional range of approximately 150 ppm to a level of 450 ppm or better (thus increasing recovery rates), significantly improved levels of silica contamination in the ion-exchanged polished permeate are achieved. New Ultra Pure Water (UPW) systems utilizing this process will have thirty to fifty percent lower capital costs and at least twenty five percent lower operating costs compared to conventional UPW systems.

Claims117

Dependent claims

A process for treatment of a feedwater stream in membrane separation equipment, said membrane separation equipment comprising at least one unit having a membrane separator, to produce a low solute containing product stream and a high solute containing reject stream, said process comprising:

(a) providing a feedwater stream containing solutes therein, said solutes comprising
(i) hardness,
(ii) alkalinity, and
(iii) at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution;
(b) concentrating said feedwater stream in a first unit of said membrane separation equipment after reducing the tendency of said feedwater to form scale when said feedwater is concentrated to a preselected concentration factor at a selected pH, by effecting, in any order, two or more of the following:
(i) removing hardness from said feedwater stream;
(ii) removing substantially all alkalinity associated with hardness from said feedwater stream, wherein TOC is rejected at least 95%
(iii) removing dissolved gas from said feedwater stream, whether initially present or created during said hardness or said alkalinity removal step;
(c) raising the pH of the product from step (a) to a selected pH of at least about 8.5, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(d) passing the product from step (c) above through said membrane separation equipment, said membrane separation equipment substantially resisting passage of dissolved species therethrough, to concentrate said feedwater to said preselected concentration factor, to produce
(i) a high solute containing reject stream, and
(ii) a low solute containing product stream.

9 more elements

(a) providing a feedwater stream containing solutes therein, said solutes comprising
(i) hardness,
(ii) alkalinity, and
(iii) at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution;
(b) concentrating said feedwater stream in a first unit of said membrane separation equipment after effectively eliminating the tendency of said feedwater to form scale when said feedwater is concentrated to a preselected concentration factor at a selected pH, by effecting, in any order, two or more of the following:
(i) removing hardness from said feedwater stream
(ii) removing substantially all non-hydroxide alkalinity from said feedwater stream;
(iii) removing dissolved gases, whether initially present or created during said hardness or said alkalinity removal step;
(c) raising the pH of the product from step (a) to a selected pH of at least about 8.5 by adding a selected base thereto, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(d) passing the product from step (c) above through said membrane separation equipment to produce a reject stream and a product stream, said membrane separation equipment substantially resisting passage of dissolved species therethrough, to concentrate said feedwater to said preselected concentration factor, to produce
(i) a high solute containing reject stream, and
(ii) a low solute containing permeate product stream, wherein TOC is rejected at least 95%.

9 more elements

Apparatus for treatment of a feedwater stream, said feedwater stream characterized by the presence of (I)hardness, (ii)alkalinity, and (iii)at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution, to produce a low solute containing product stream and a high solute containing reject stream, said apparatus comprising, in order by feedwater flow:

(a) pretreatment equipment for effectively eliminating the tendency of said feedwater to form scale when said feedwater is concentrate to desire concentration factor at a selected pH, comprising, in any order two or more of the following:
(I) at least one softener for removing substantially all hardness from said feedwater stream
(ii) at least one de-alkalizer fro removing substantially all alkalinity associated with hardness from said feedwater stream, said de-alkalizer characterized by the absence of anion-exchange unit;
(iii) a degasifier for removing at least some dissolved gases, whether initially present or created during said hardness or said alkalinity removal step;
(b) chemical addition apparatus for raising the pH of the product form step (a) to a selected pH of at least about 8.5 by adding a selected base thereto, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(c) one or more reverse osmosis membrane units, said one or more reverse osmosis membrane units, for treating the feedwater to produce a reject stream and a product stream, said one or more reverse osmosis membrane units substantially resisting passage of ionized species therethrough, to concentrate said feedwater to said preselected concentration factor.

3 more elements

A method for simultaneously increasing the permeate production (flux) and the permeate purity of an existing reverse osmosis system treating a feedwater stream in at least one reverse osmosis system unit, to produce a low solute containing product stream and a high solute containing reject stream, said method comprising:

(a) providing a feedwater stream containing solutes therein, said solutes comprising:
(i) hardness,
(ii) alkalinity, and
(iii) at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution;
(b) concentrating said feedwater stream in a first of said at least one reverse osmosis units after reducing the tendency of said feedwater to form scale when said feedwater is concentrated to a preselected concentration factor at a selected pH, by effecting, in any order, one or more of the following:
(i) removing hardness from said feedwater stream
(ii) removing substantially all alkalinity associated with hardness from said feedwater stream;
(iii) removing dissolved carbon dioxide from said feedwater stream, whether present initially or created during said hardness or said alkalinity removal step;
(c) raising the pH of the product from step (b) to a selected pH of at least about 8.5, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(d) passing the product from step (c) above through said reverse osmosis system, said reverse osmosis system of the type which substantially resists passage of dissolved species therethrough, to concentrate said feedwater to said preselected concentration factor, to produce
(i) a high solute containing reject stream, and
(ii) a low solute containing product stream, and
(iii) producing said product stream at a production rate (flux) of at least about 20 gallons per square foot per day.

10 more elements

A method for simultaneously increasing the permeate production (flux) and the permeate purity of an existing membrane separation system treating a feedwater stream in at least one membrane separation system that produces a low solute containing product stream and a high solute containing reject stream, said method comprising:

(a) providing a feedwater stream containing solutes therein, said solutes comprising:
(i) hardness,
(ii) alkalinity, and
(iii) at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution;
(b) concentrating said feedwater stream in a first unit of said membrane separation system after effectively eliminating the tendency of said feedwater to form scale when said feedwater is concentrated to a preselected concentration factor at a selected pH, by effecting, in any order, one or more of the following:
(i) removing an effective amount of hardness from said feedwater stream
(ii) removing an effective amount of alkalinity from said feedwater stream;
(iii) removing dissolved gases, whether initially present or created during said hardness or said alkalinity removal step;
(c) raising the pH of the product from step (b) to a selected pH of at least about 8.5 by adding a selected base thereto, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(d) passing the product from step (c) above through said membrane separation system to produce a reject stream and a product stream, said membrane separation equipment of the type which substantially resists passage of dissolved species therethrough, to concentrate said feedwater to said preselected concentration factor, to produce
(i) a high solute containing reject stream, and
(ii) a low solute containing product stream and
(iii) producing said product stream at a production rate (flux) of at least about 20 gallons per square foot per day.

10 more elements

A method for simultaneously providing high permeate production (flux) and high permeate purity in a reverse osmosis system treating a feedwater stream, to produce a low solute containing product stream and a high solute containing reject stream, said method comprising:

(a) providing a feedwater stream containing solutes therein, said solutes comprising:
(i) hardness,
(ii) alkalinity, and
(iii) at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution;
(b) before introducing said feedwater stream into said reverse osmosis system, reducing the tendency of said feedwater to form scale when said feedwater is concentrated to a preselected concentration factor at a selected pH, by effecting, in any order, one or more of the following:
(i) removing hardness from said feedwater stream
(ii) removing substantially all non-hydroxide alkalinity from said feedwater stream;
(iii) removing carbon dioxide from said feedwater stream, whether present initially or created during said hardness or said alkalinity removal step;
(c) raising the pH of the product from step (b) to a selected pH of at least about 8.5, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(d) passing the product from step (c) above through said reverse osmosis system, said reverse osmosis system substantially resisting passage of dissolved species therethrough, to concentrate said feedwater to said preselected concentration factor, while operating said reverse osmosis system at a flux in excess of 15 gallons per square foot per day to produce
(i) a high solute containing reject stream, and
(ii) a low solute containing product stream.

9 more elements

A process for treatment of a feedwater stream in membrane separation equipment comprising at least one unit having a membrane separator to produce a low solute containing product streams and a high solute containing reject stream, said process comprising:

(a) providing a feedwater stream containing solutes therein, said solutes comprising
(i) hardness,
(ii) alkalinity, and
(iii) at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution;
(b) concentrating said feedwater stream in a first unit of said membrane separation equipment after reducing the tendency of said feedwater to form scale when said feedwater is concentrated to a preselected concentration factor at a selected pH, by effecting, in any order, two or more of the following:
(i) removing an effective amount of hardness from said feedwater stream;
(ii) removing substantially all alkalinity associated with hardness, from said feedwater stream;
(iii) removing dissolved gas from said feedwater stream, whether initially present or created during said hardness or said alkalinity removal step;
(c) raising the pH of the product from step (b) to a selected pH of at least about 8.5, to urge said at least one molecular species which is sparingly ionized when in neutral or near neutral pH aqueous solution toward increased ionization;
(d) passing the product from step (c) above through membrane separation equipment, said membrane separation equipment substantially resisting passage of dissolved species therethrough, to concentrate said feedwater to said preselected concentration factor.

7 more elements

In a process for the purification of an aqueous solution comprising solutes and solvent by using membrane separation equipment to increase the concentration of said solution to a preselected concentration factor by passing a portion of said aqueous solution through a semi-permeable membrane in a first unit of said membrane separation equipment to produce a product stream, and retaining at least a portion of said aqueous solution in said first unit of said membrane separation equipment to increase the concentration of a preselected solute to a preselected concentration factor in said retained portion of said aqueous solution,

the improvement which comprises controlling solutes, hardness, alkalinity, and carbon dioxide in said aqueous solution to a level were the tendency to form scale is effectively eliminated at said preselected concentration factor, by
(a) prior to feed of said aqueous solution to said first unit of said membrane separation equipment, optimally, in any order,
(I) minimizing hardness of said aqueous feed solution,
(ii) minimizing alkalinity of said aqueous feed solution, and
(iii) minimizing carbon dioxide dissolved or suspended therein, and
(b) then, after step (a), increasing the pH of said aqueous feed solution to at least 8.5, and wherein TOC is rejected by said semi-permeable membrane by at least 95%.

3 more elements

Dependencies are inferred from the claim text.

Method and apparatus for high efficiency reverse osmosis operation

Life of this patent

Method and apparatus for high efficiency reverse osmosis operation

Life of this patent

Abstract

Claims117