WO2001083376A2

WO2001083376A2 - Method of reducing contaminants in drinking water

Info

Publication number: WO2001083376A2
Application number: PCT/US2001/013619
Authority: WO
Inventors: Ehud Levy
Original assignee: Selecto, Inc.
Priority date: 2000-04-28
Filing date: 2001-04-27
Publication date: 2001-11-08
Also published as: AU2001255743A1; WO2001083376A3

Abstract

This invention provides a method making water safer for use by humans and animals by reducing the levels of a number of different contaminants present in the water, by contacting the water with a first purification medium comprising alumina; and contacting the water with a second purification medium comprising zirconia.

Description

METHOD OF REDUCING CONTAMINANTS IN DRINKING WATER

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to methods for water filtration using a combination of

filtration media. More particularly, the invention relates to methods for water filtration

wherein the water passes through filtration media containing alumina and through a

filtration media containing zirconia.

2. Description of Related Art

The chemistry of potable drinking water varies significantly from location to

location throughout the United States. Many municipal drinking water plants are

delivering drinking water from wells and ground water that contains arsenic, lead, NOC

(Volatile Organic Chemicals) such as chloroform, mercury and other contaminants.

Arsenic and NOC have also been found in drinking water in many other countries.

Arsenic species are being used or have been used in the manufacture of medicine and

cosmetics among other things, and have been used as agricultural insecticides. They have

also been used as desiccants, in rodenticides and in herbicides. Arsenic contaminants are

primarily found as an arsenate or an arsenite in drinking water. Chloroform, as a member

of the trihalomethanes family, is often a major byproduct of chlorination-disinfection

processes used in water treatment. These contaminants are considered health hazards

which can cause cancer, skin discoloration, liver disease and a host of other health

problems. To reduce arsenic from drinking water, municipal water plants use different

techniques such as redux, adsorption and precipitation. The most common media for

adsorption used today is alumina or weak acid ion exchange resins. Alumina works well

to reduce arsenic levels from about one part per million to about five parts per billion.

However, alumina media for such purposes is usually used in small applications such as

point-of-use water filters, and such use is limited. This is due primarily to the poor

kinetics of such filters. Ion exchange resins suffer the same limitation. Another

technique employed to remove arsenic is reverse osmosis which is very effective.

However, it is an expensive treatment which causes a considerable amount of water to be

wasted. In some cases this technique has experienced difficulty due to a change in the

oxidation state of the arsenic contaminate from an arsenate to an arsenite. Municipalities

have been struggling for a number of years, using different techniques of oxidizing

arsenic for removal by their water plants. The cost for doing so in capital investment is

extremely high and at present over six hundred municipalities continue to experience

substantial difficulty in their efforts to reduce arsenic content from drinking water. The

cost of doing so is for many small municipalities, prohibitive due to the complexity of

existing methods which are adapted from large scale plants. Moreover, many proposed

treatments adversely affect the taste and color of the water and may produce unknown

byproducts.

SUMMARY OF THE INVENTION

This invention provides a method making water safer for use by humans and

animals by reducing the levels of a number of different contaminants present in the water, by contacting the water with a first purification medium comprising alumina; and

contacting the water with a second purification medium comprising zirconia. Treatment

in this manner can reduce the levels of heavy metals in the water, in particular arsenic

levels, by amounts ranging from about 20% to about 100%, without any concomitant

modification or degradation of the water pH or water hardness. In addition, the treatment

method of the invention can reduce the levels of volatile organic compounds, such as

chloroform, and can provide large scale reductions in the level of bacterial contamination,

particularly contamination by coliform and pseudomonal bacteria.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The first purification medium used in the method of the invention contains

alumina. Acid- washed alumina has been found to be suitable in this regard, and is

described in U.S. Patent No. 5,133,871, issued July 28, 1992, the entire contents of which

are hereby incorporated by reference. In particular, acid-washed alumina having particle

sizes of about 28 to about 48 mesh (and may have an average particle size in this range)

and BET surface area of about 160 to about 260 m²/g has been found to be suitable as the

first purification medium containing alumina.

The second purification material contains zirconia. Suitable zirconia-containing

purification materials include those disclosed in U.S. Serial No. 08/819,999, filed March

18, 1997, the entire contents of which are hereby incorporated by reference. The zirconia

may be in powdered form, or in granular form. If in powdered form, the zirconia

typically has a particle size distribution ranging from about 5 to about 100 micron, more

particularly from about 10 to about 60 micron, and typically has a mean particle size of

about 40 micron or larger, more particularly about 60 micron. In larger scale systems, granular zirconia may be more desirable. In these

situations, the zirconia is generally of a particle size of about 20 to about 100 mesh.

The zirconia used in the second purification medium desirably has pore sizes

ranging from about 5 Angstroms to about 500 Angstroms, more particularly, from about 5

Angstroms to about 60 Angstroms for particularly efficient arsenic removal. The BET

pore volume of the zirconia typically ranges from about 300 cmVg to about 800 cmVg,

more particularly from about 300 cm³/g to about 600 cm³/g. Zirconia having large pores

(e.g., over 60 Angstrom) have been found to lose their removal capacity for arsenic by

about 60%. Those of skill in the art will recognize that the pore size may be varied within

the above-desired ranges, or even outside of it, in order to optimize removal efficiency for

the heavy metal of interest.

The zirconia may desirably be formed into a cartridge containing other

components, such as activated carbon, or other adsorbents, as well as an optional binder.

While the relative amounts of each component in the cartridge are substantially variable,

one suitable composition contains, by weight, based on the total weight of cartridge

adsorbent, about 5% to about 15% zirconia, about 70 % activated carbon, and about 15%

to about 25% organic binder. The powder is heated for 30-60 minutes and then

compressed for 15 minutes at 60-100psi.

In use, the method of the invention simply involves passing the water to be treated

through the alumina containing purification medium and then through the zirconia

containing purification medium. If the purification medium is in the form of cartridges,

the cartridges may be of any suitable shape generally adapted or used in water

purification. Examples include cylindrical or toroidally shaped cartridges. Generally the cartridges are disposed near or contain one or more inlets and/or outlets for the water,

which is caused to flow over and/or through the cartridge material. The alumina

containing purification material may be disposed adjacent to the zirconia containing

purification material (e.g., in the same or an adjacent cartridge), or in a separate vessel,

connected so that water leaving the alumina containing purification material flows over

and/or through the zirconia containing purification material.

The invention can be more fully understood by reference to the following

nonlimiting examples of particular embodiments thereof.

EXAMPLES

Example 1 - Reduction of Arsenic

Tap water (Suwanee, GA) was contaminated with arsenic trioxide to a

concentration of about 200 to about 300 ppb of arsenic. The water is passed through a

first filter cartridge containing acid washed alumina. Effluent from this treatment is

passed through a filter cartridge containing ultrapure zirconium, substantially free from

radioactive species, organic compounds, and metal oxides.

The level of arsenic was measured by a Perkin Elmer atomic absorption

spectrometer. Standard atomic absorption conditions for As was applied in the test with

EDL light source. There was a linear relationship between [As] and AA absorbance in

range of 5- 100 part per billion. The influent was diluted to the specified concentration

before the AA measurements. 20L of the solution was used to determine the As

concentration.

The properties of the test water are given below. The testing was done using a

test method for arsenic reduction established by ANSI/NSF - Standard 53.

As indicated above, the influent water had a concentration of 200-300 ppb of As.

The effluent water had an As concentration under 20 ppb for 2500 gallon test. Arsenic

was found to be reduced from 250 ppb to ~2 ppb and the average reduction percentage is

99.2%. The following table summarizes the results:

Example 2 - Reduction of Volatile Organic Chemicals (VOCs)

Water as described above in Example 1, but deliberately contaminated with

chloroform instead of arsenic trioxide, was passed through the alumina and zirconia filter cartridges described above in Example 1. The test water had the following

characteristics:

VOC determination was carried out using a GC. The testing methodology for

VOC reduction used was that specified in ANSI/NSF Standard 53-1999.

Influent water had 300 ppb of chloroform and effluent had an undetectable

chloroform concentration. The average reduction percentage was 99.9%. The following

table summarizes the results:

Example 3 - Reduction of bacteria Water tested for bacteria reduction had the following characteristics:

The test water was seeded with challenge colonies of the indicated bacteria, and

passed through a purification system containing the alumina containing purification

medium and the zirconia containing purification medium described in Example 1 above.

The resulting water was tested as indicated above for the presence of the indicated

bacteria. Test results show the very effective removal of bacteria by the media. The

percentage of the reduction is 100%. The results are given in following table:

This large scale reduction in the numbers of microorganisms in the water was

unexpected.

The use of the purification method of the invention is a substantial and unexpected

advance over what has hitherto been known in the art. In particular, the use of an acid

washed gamma alumina as the first purification material and zirconia as the second

purification material resulted in about a 20 fold improvement in the kinetics of filtration,

and about a 30 fold improvement in filtration capacity. Using these purification materials

separately to treat water heavily contaminated with arsenic, it was found that alumina

reduced the arsenic level from 200 ppb to 60 ppb in 200 gallons of water at a flow rate of

1 gal./min. The zirconia/carbon purification material, used alone, reduced the arsenic

level from 200 ppb to 30 ppb in 300 gallons of water at the same flow rate. However,

when the alumina purification material is used to treat water and followed by treatment

with the zirconia purification material, the arsenic level was reduced from 200 ppb to 1

ppb for amounts of water ranging between 3,000 gallons and 6,000 gallons at the same

flow rate. Moreover, this synergistic effect occurred without significant filter breakage.

In addition, efficiency of metal removal in known processes is often inversely

related to flow rate. The present invention allows increased efficiencies even at high flow

rates. For instance, about 100 g. of zirconia purification material was tested in a static

column, and was found to reduce arsenic levels from about 600 ppm to 1 ppb at a flow

rate of 1 ml/min. However, when the flow rate increased, the efficiency of arsenic

removal decreased. When the alumina purification material was used prior to the zirconia purification material, the efficiency of arsenic removal was improved even at the higher

flow rates.

While not wishing to be bound by any theory, it is believed that the alumina may

add a positive charge or cause redox reactions of metal species, such as arsenic, and

impart charges to VOC molecules and bacteria, which causes them to become adsorbed

onto the zirconia. For instance, it is known that arsenic can be oxidized from arsenate to

arsenite in the presence of high concentrations of chlorine, and a similar effect may occur

in the presence of the alumina purification material used in the invention. Heavy metal

species that undergo similar changes in oxidation number under similar treatment

conditions would also be removable by the process of the invention, and a determination

of the specific operating parameters for such removal processes could be determined by

optimization based upon the changes set forth herein.

The invention having been thus described with respect to its specific

embodiments, it will be apparent to those of skill in the art that various modifications and

adaptations of the invention can be made, and that various equivalents thereto exist.

These are intended to be included by the appended claims, and by the scope of

equivalents thereto.

Claims

WHAT IS CLAIMED IS:

1. A method for reducing contaminants in water, comprising:

contacting the water with a first purification medium comprising alumina; and

contacting the water with a second purification medium comprising zirconia.

2. The method of claim 1, wherein the water is contacted with the first purification

medium, removed from the first purification medium, then contacted with the second

purification medium, and removed from the second purification medium.

3. The method of claim 2, wherein the water removed from the second purification

medium is purified potable water.

4. The method of claim 1, wherein the contaminants comprise heavy metals,

halogenated organic compounds, bacteria, or a combination thereof.

5. The method of claim 4, wherein the bacteria comprise coliform bacteria,

pseudomonal bacteria, or combinations thereof.

6. The method of claim 5, wherein the bacterial comprise E. coli, P. aeruginosa, or

combinations thereof.

7. The method of claim 4, wherein the heavy metals comprise arsenic.

8. The method of claim 4, wherein the halogenated organic compounds comprise one

or more halogenated hydrocarbons.

9. The method of claim 8, wherein the halogenated hydrocarbon comprises

chloroform.

10. The method of claim 1 , wherein the first purification medium comprises acid-

washed alumina.

11. The method of claim 10, wherein the acid- washed alumina has a particle size in

the range of about 24 mesh to about 48 mesh.

12. The method of claim 10, wherein the acid- washed alumina has an average particle

size in the range of about 24 mesh to about 48 mesh.

13. The method of claim 10, wherein the acid- washed alumina has a BET surface area

of about 160 to about 260 m²/g.

14. The method of claim 1 , wherein the second purification medium comprises

zirconia in a powdered form.

15. The method of claim 14, wherein the powdered zirconia has a particle size

distribution ranging between about 5 to about 100 microns.

16. The method of claim 15, wherein the powdered zirconia has a particle size

distribution ranging between about 10 and about 60 microns.

17. The method of claim 14, wherein the powdered zirconia has a mean particle size

of about 40 microns or larger.

18. The method of claim 17, wherein the mean particle size is about 60 microns.

19. The method of claim 1 , wherein the second purification medium comprises

zirconia having pore sizes in the range from about 5 Angstroms to about 500 Angstroms.

20. The method of claim 19, wherein the pore sizes range from about 5 Angstroms to

about 60 Angstroms.

21. The method of claim 1 , wherein the second purification material comprises

zirconia having a BET pore volume ranging from about 300 cm³/g to about 800 cmVg.

22. The method of claim 21, wherein the BET pore volume ranges between about 300

cm³/g and about 600 cmVg.

23. The method of claim 1 , wherein the first purification medium comprises a mixture

of an alumina, an aluminosilicate gel, and a silica gel.

24. The method of claim 1, wherein the second purification medium comprises

granular zirconia.

25. The method of claim 24, wherein the granular zirconia has a particle size in the

range of about 28 to about 100 mesh.

26. The method of claim 1 , wherein the second purification medium comprises

zirconia, activated carbon, and a binder therefor.

27. The method of claim 26, wherein the zirconia is present in an amount of about 5

wt% to about 15 wt%, the activated carbon is present in an amount of about 70 wt%, and

the organic binder is present in an amount of 15 wt% to about 25 wt%, based on the total

composition.

28. A method for reducing contaminants in water, comprising:

contacting the water with a purification material comprising zirconia.

29. The method of claim 28, wherein the water has been previously contacted with

another purification material comprising alumina.

30. The method of claim 28, wherein the purification material further comprises

activated carbon.

31. The method of claim 30, wherein the purification material further comprises an

organic binder.

32. The method of claim 28, wherein the contaminants comprise arsenic.

33. The method of claim 28, wherein the contaminants comprise bacteria.

34. The method of claim 33, wherein the bacteria comprise E. coli.