METHOD AND APPARATUS FOR WATER TREATMENT

Abstract

A method and apparatus for the treatment of water and, more particularly, to the mineralization of water in order to improve pH, hardness, turbidity, and/or alkalinity is described. More particularly, a system is provided for the treatment of water that needs additional hardness, alkalinity, and/or pH adjustment while also meeting turbidity requirements. The use of sodium hydroxide and other methods for avoiding turbidity problems can be eliminated and/or minimized.

Claims

1. A system for water treatment, comprising: a first channel providing a flow of water; a second channel that intersects said first channel and provides a flow of carbonic acid into the flow of water of said first channel; a third channel intersecting said first channel to provide a flow of calcium hydroxide into the flow of water provided by first channel, said second channel intersecting downstream of the intersection of said second channel and said first channel; and an agitator positioned downstream of the intersection of said third channel and said first channel, said agitator configured for decreasing the turbidity of the water by moving the agitator through the water and calcium hydroxide, or moving the water and calcium hydroxide through the agitator, so as to shear the water at a rate sufficient to lower the turbidity.

2. The system for water treatment as in claim 1, wherein the second channel and third channel are separated by a predetermined distance sufficient for the carbonic acid to lower the pH of the flow of water before the addition of calcium hydroxide.

3. The system for water treatment as in claim 1, wherein the predetermined distance is in the range of 10 to 80 feet.

4. The system for water treatment as in claim 1, wherein the agitator comprises an impeller rotated or moved relative to the water and calcium hydroxide so as to shear the water at a rate sufficient to lower the turbidity.

5. The system for water treatment as in claim 4, further comprising a tee, wherein the impeller is located within the tee.

6. The system for water treatment as in claim 4, wherein the impeller is rotated at a speed in the range of 300 rpm to 5000 rpm.

7. The system for water treatment as in claim 4, wherein the impeller comprises a disk defining a plane and a plurality of blades carried by the disk and oriented out of the plane.

8. The system for water treatment as in claim 1, wherein the agitator does not affect the pH, hardness, or alkalinity of the water.

9. The system for water treatment as in claim 1, wherein the flow of calcium hydroxide comprises calcium hydroxide and water.

10. The system for water treatment as in claim 1, wherein the agitator decreases the turbidity of the water to 1 NTU or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0024] FIG. 1 provides a flow chart of steps according to an exemplary method of the present invention.

[0025] FIG. 2 provides a perspective view of an exemplary embodiment of a rotor as may be used to provide mechanical agitation according to the present invention.

[0026] FIG. 3 provides a perspective view of an exemplary embodiment of an apparatus for water treatment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention relates to a method and apparatus for the treatment of water and, more particularly, to the mineralization of water in order to improve pH, hardness, turbidity, and/or alkalinity. More particularly, the present invention provides for the treatment of water that needs additional hardness, alkalinity, and/or pH adjustment while also meeting turbidity requirements. The use of sodium hydroxide to address turbidity problems can be avoided. The blending of water from an underground or previously treated source can be minimized or avoided.

[0028] For purposes of describing the invention, reference now will be made in detail to embodiments and/or methods of the invention, one or more examples of which are illustrated in or with the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features or steps illustrated or described as part of one embodiment, can be used with another embodiment or steps to yield a still further embodiments or methods. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0029] As used herein, the following definitions apply:

[0030] Alkalinity refers to the buffering capacity of water and, more particularly, to the ability of water to neutralize acid and bases and thereby maintain a fairly stable pH.

[0031] Hardness refers to the amount of multivalent cations in watertypically metals such as Mg.sup.2+ and Ca.sup.2+.

[0032] Turbidity refers to the cloudiness or haziness water caused by the presence of suspended particles in the water. Turbidity can be reported in nephelometric turbidity units of NTU. By way of example, certain drinking water applications require an NTU of less than 1.0.

[0033] FIG. 1 provides a flow chart illustrating an exemplary method of the present invention. In step 102, water is provided that needs treatment. More specifically, water is provided that needs hardness e.g., the addition of multivalent cations such as Mg.sup.2+ and Ca.sup.2+. The water may also need pH, turbidity, and alkalinity adjustment.

[0034] By way of example, the water provided for treatment may comprise the permeate from membrane treatment such as e.g., RO filtered water. Such water typically will have an acceptable turbidity level but an unacceptably low level of hardness. For some RO permeates, the water may also have an unacceptable low pH due to the addition of acid(s) for treatment of the membrane. However, water that needs treatment may also come from other sources as well including e.g., surface water sources, underground water sources, or from other water treatment systems that have left the water at unacceptable levels of hardness.

[0035] In step 104, the pH of the water is lowered by the addition of carbon dioxide or carbonic acid to the water. Carbonic acid (H.sub.2CO.sub.3) is formed from the addition of carbon dioxide into the water. More particularly, when dissolved in water, carbon dioxide will exist in equilibrium with carbonic acid according to the following equation:

CO.sub.2+H.sub.2OH.sub.2CO.sub.3

Devices exist for the creation of carbonic acid in this manner. For example, such a device is sold by GrayTech Carbonic, Inc. of Union Star, Mo.

[0036] After carbonic acid is added to the water, in step 106, time is allowed for the lowering of the pH by such addition. For example, if the water being treated is provided as a flow in a pipe or other channel, sufficient distance is allowed for the water to properly lower the pH before step 108 is conducted. Preferably, the pH is lowered to a value in the range of about 2 to about 6. Still more preferably, the pH of the water is lowered to a value in the range of about 3 to about 5.

[0037] After the pH has been adjusted, slaked lime or Ca(OH).sub.2 is added to the water. Preferably, this step is conducted by the addition of lime slurryi.e. slaked lime that has already been placed into water before the addition to the water that is being treated. The addition of Ca(OH).sub.2 mineralizes the water to raise both hardness and alkalinity. For example, the slaked lime will react with carbonic acid in the water as follows:

H.sub.2CO.sub.3Ca(OH).sub.2CaCO.sub.3+2H.sub.2O

Additionally, to the extent carbon dioxide is present in the water, the slaked lime with react with the same as follows:

Ca(OH).sub.2+CO.sub.2.fwdarw.CaCO.sub.3+H.sub.2O

[0038] By either of the above reactions, the soluble calcium carbonate (CaCO.sub.3) is provided into the water. This in turn provides the needed increase in both hardness and alkalinity in that the multivalent cation Ca.sup.2+ is provided along with CO.sub.3.sup.2. In addition, calcium carbonate can also react with water and carbon dioxide in the water to form the soluble calcium bicarbonate as follows:

CaCO.sub.3CO.sub.2+H.sub.2O.fwdarw.Ca(HCO.sub.3).sub.2

Again, this operates to improve both hardness and alkalinity by providing Ca.sup.2+ into the water along with HCO.sub.3.sup.1. Preferably, slaked lime is added in step 108 until the alkalinity and hardness are in a range of about 10 ppm to about 80 ppm (parts per million). While it is preferably to add the lime as a slurry into the water, slaked lime may be added directly into the water as well.

[0039] Unfortunately, the addition of Ca(OH).sub.2 to the water (whether in a slurry or as a solid) will also increase the water's turbidity to a level that is likely unacceptable. For example, the turbidity can be increased to a level above 1 NTUwhich is not acceptable in certain applications. Accordingly, in order to improve the turbidity, mechanical agitation is provided to the water in step 110. As used herein, mechanical agitation refers to mixing using an impeller or other device that is rotated or moved through the water so as to shear the water, preferably at a high rate of shear.

[0040] FIG. 2 provides an exemplary embodiment of an impeller 200 as may be used with the present invention to provide mechanical agitation. As shown, impeller 200 includes disk 210, disk 220, and disk 230 mounted onto shaft 205. Disk 210 includes a plurality of blades 215, disk 220 includes a plurality of blades 225, and disk 230 includes a plurality of blades 235. Blades 215, 225, and 235 are oriented out of the plane of their respective disk and alternate between e.g., a turn up and a turn down. As such, during operation, blades 215, 225, and 235 provide multiple edges for the shearing of the water as shaft 205 is rotated. Impeller 200 is provided, for example, by INDCO of New Albany, Ind. While not intended to be bound by any particular theory, it is believed that the shear provided by the plurality of blades 215, 225, and 235 provides for increased shearing and/or increased collisions with particles in the water so as to assist in reducing the turbidity. Impeller 200 is provided by way of example only. Using the teachings disclosed herein, it will be understood that other configurations and designs for impeller 200 may be used as well to provide mechanical agitation of the water in step 110.

[0041] FIG. 3 shows an apparatus 300 for water treatment that incorporates impeller 200 according to an exemplary embodiment of the present invention. Through a first channel 335, a flow of water 305 in need of treatmenti.e., having a hardness that is too lowis provided. A second channel 325 intersects first channel 335 and provides a flow 310 of carbonic acid or carbon dioxide gas into water 305. A third channel 330 also intersects first channel 335 and provide a flow 315 of calcium hydroxide (in the form a slake lime slurry) into the flow of water 305 in first channel 335.

[0042] Distance D represents a predetermined distance by which the intersection of third channel 330 is positioned downstream of the intersection of second channel 325 with first channel 335. This distance provides enough time for the carbonic acid to lower the pH of the water flow 305 before the addition of calcium hydroxide. This amount will vary with application but is typically in the range of 10 to 80 feet. Other distances may be used as well.

[0043] As flow 305 continues downstream, it encounters impeller 200 within a tee 340. Impeller 200 is driven by a motor 345. Shaft 205 extends through a bearing 355 mounted in a flange 350, which is secured to tee 340 using bolts 360. In some embodiments, shaft 205 may extend down to the bottom of tee 340 where it may be received by a bearing or other device configured for receipt of the end of shaft 205 to provide additional stability.

[0044] A range of speeds for the rotation R of impeller 200 may be used. For example, a range of 300 rpm to about 5000 rpm is used. Alternatively, a range of 1000 to 2000 rpm may be used. The precise speed of rotation will depend upon a variety of factors including the design of impeller 200, the flow rate of water being agitated, the geometry of the channel or other device in which impeller 200 is placed, and other factors as well. These variables can be adjusted such that using mechanical agitation, the turbidity of the water 320 exiting device 300 can be reduced to an acceptable NTU value in step 110. For example, NTU can be reduced to a value of 1.0 or lower.

[0045] Apparatus 300 is provided by way of example only. As will be understood by one of ordinary skill in the art using the teachings disclosed herein, other devices may be configured as well to provide water treatment according to the present invention. Preferably, apparatus 300 is positioned downstream of a filtering process such as e.g., an RO filtering process. However, for some applications, apparatus 300 or other devices for water treatment according to the present invention may be positioned upstream of the filtering process as well.

[0046] As stated above, apparatus 300 uses mechanical agitation to provide shear mixing and lower the turbidity of the water being treated. One approach to understanding shear mixing is a measurement that relates to how much power is transferred into mechanical agitation. For example, one such measurement is referred to as the root mean velocity gradient or G-value. Proposed by Camp and Stein (1943), G-value refers to mechanical power to facilitate turbulent mixing and depends upon power, volume (i.e. the amount mixed or the container size where mixing occurs), and the viscosity of water (). The viscosity of water is a variable factor that is dependent upon water temperature, which can vary widely from seasonal changes or the location of the water plant.

[0047] G-value can be calculated as follows:

[00001]$G=\sqrt{\frac{P}{.Math..Math.V}}$ [0048] where: [0049] G=velocity gradient (sec.sup.1) [0050] P=Power or energy imparted to water (hp550) lb-ft [0051] =Dynamic viscosity of water (50 F.) [0052] (50 F.) 2.73010.sup.5 lb/ft.sup.2 [0053] (60 F.) 2.34410.sup.5 lb/ft.sup.2 [0054] (70 F.) 2.03410.sup.5 lb/ft.sup.2 [0055] (80 F.) 1.79110.sup.5 lb/ft.sup.2 [0056] V=Liquid Volume m.sup.3 or ft.sup.3

[0057] For example, consider two colloidal particles, 0.05 ft apart, moving in a vessel. Each particle is moving at a velocity of 4 ft/sec relative to each other.

[00002]$G=\frac{4.Math..Math.\mathrm{ft}.Math.\text{/}.Math.\sec }{\mathrm{.05}.Math..Math.\mathrm{ft}}=\frac{80.Math..Math.\mathrm{ft}.Math.\text{/}.Math.\sec }{\mathrm{ft}}=80.Math.\frac{1}{\sec }=80.Math..Math.{\sec }^{-1}$

[0058] The greater the G-value, the faster the particles will collide. In a water treatment plant, for example, a flash mix basin can have G-values of 1000-5000 sec.sup.1, while the slower mixing flocculation basins will have G-values of 20-100 sec.sup.1.

[0059] In order to obtain the desired reduction in turbidity using apparatus 300, a G-value of about 5000 or greater is preferred although other values may be used depending upon the application and the processing time available. By way of example, using an impeller similar to impeller 200, with a 5 inch diameter blade 225, in a tee 340 connected to an 8 inch diameter pipe for first channel 335, a G-value of 11771.2 sec.sup.1 can be obtained with a 1 hp motor. Such configuration and G-value were applied experimentally and found to be effective at e.g., lowering the turbidity of RO permeate to an acceptable NTU when previously treated with carbonic acid and slaked lime as described above.

[0060] While the present subject matter has been described in detail with respect to specific exemplary embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.