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| United States Patent |
6,093,422 |
| Denkewicz, Jr. , et al. |
July 25, 2000 |
Biocidal compositions for treating water
Abstract
The present invention is directed to a biocidal water treatment composition,
water treatment apparatus, and method of treating water to reduce levels of
pathogens. The composition contains sources of copper, zinc, and silver metal
ions within a crosslinked polymer matrix. Examples of these ion sources include
copper sulfate, zinc sulfate, and silver nitrate. An example of the crosslinked
polymer matrix is crosslinked chitosan, which also serves to clarify the water
and release the metal ions over time. The product is easy to manufacture, and
allows the use of decreased halogen sanitizer, as well as decreased copper ion,
thereby decreasing the likelihood of staining. The product simultaneously
provides good bactericidal and algaecidal properties, despite low levels of
copper ion and low chlorine levels.
| Inventors: |
Denkewicz, Jr.; Raymond P. (Warwick,
RI); Senderov; Ernest E. (Conshohocken, PA); Grenier; Joseph
W. (North Providence, RI) |
| Assignee: |
Zodiac Pool Care, Inc. (Smithfield, RI)
|
| Appl. No.: |
097643 |
| Filed: |
June 16, 1998 |
| Current U.S. Class: |
424/618; 424/619; 424/630;
424/632; 424/634; 424/635; 424/641; 514/54; 514/55 |
| Intern'l Class: |
A01N 059/16; A01N 059/20; A01N
043/04 |
| Field of Search: |
210/748,764,749
424/618,619,630,632,634,635,641 514/54,55 |
References Cited [Referenced
By]
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Samad et al. |
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Momont et al. |
210/704. |
| Foreign Patent Documents |
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Jul., 1992 |
EP. |
|
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Oct., 1996 |
JP. |
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Mar., 1997 |
ZA. |
|
| WO 97/37939 |
Oct., 1997 |
WO. |
|
Other References
International Search Report in corresponding
International Application No. PCT/US98/26773.
Grenier and Denkewicz,
"Improved Test Medium for the Evaluation of Algaecides & Algaestats
for Swimming Pools," Published in Jun. 1998 at the 2nd Annual Chemistry
Symposium, Chicago, Illinois (held Nov. 11, 1997).
|
Primary Examiner: Dees; Jose' G.
Assistant Examiner: Pryor; Alton
Attorney, Agent or Firm:
Gray; Bruce D., Russell; Dean W. Kilpatrick Stockton LLP
Parent Case Text
BACKGROUND OF THE INVENTION
This application claims priority to
Application No. 60/072,283 filed as a provisional application on Jan. 23, 1998,
by Raymond P. Denkewicz, Ernest E. Senderov and Joseph E. Grenier entitled
"Biocidal Compositions for Treating Water."
Claims
What is claimed is:
1. A composition for treating water, formed
by preparing a mixture comprising:
(a) a source of copper ion in an
amount that provides a coper concentration in the water to be treated of about
0.2(b) a sour less;
(b) a source of silver ion;
(c) a source of
zinc ion;
(d) one or more cross-linkable polymers; and
(e) a
crosslinking agent and allowing the mixture to dry to a solid composition;
wherein the source of copper ion, the source of silver ion, and the
source of zinc ion are present in amounts that provide a ratio of zinc ion
source to copper ion source ranging from about 0.5:1 to about 4:1- and a ratio
of silver ion source to copper ion source ranging from about 0.05:1 to about
2:1.
2. The composition according to claim 1, wherein the source of
copper ion is present in an amount that provides an initial copper ion
concentration in the water of about 0.2 ppm or less, and long term copper ion
concentration of about 0.1 ppm or less.
3. The composition according to
claim 1, wherein the source of copper ion is present in an amount that provides
a copper ion concentration in the water to be treated of about 0.2 to about 0.07
ppm.
4. The composition according to claim 3, wherein the source of zinc
ion is present in an amount that provides a zinc ion concentration in the water
to be treated of about 0.5 to about 0.4 ppm.
5. The composition
according to claim 4, wherein the source of silver ion is present in an amount
that provides a silver ion concentration in the water to be treated of about
0.04 to about 0.01 ppm.
6. The composition according to claim 1, wherein
the solid composition does not shrink or expand substantially as compared to the
mixture before drying.
7. The composition according to claim 1, wherein
the source of copper ion is selected from the group consisting of copper
sulfate, copper chloride, copper nitrate, copper bromide, copper fluoride,
copper metaborate, copper ammonium carbonate, copper ammonium
sulfate, copper oxalate, copper salicylate, copper acetate, copper
formate, copper gluconate, and mixtures thereof.
8. The composition
according to claim 1, wherein the source of silver ion is selected from the
group consisting of silver nitrate, silver sulfate, silver fluoride, silver
chlorate, silver perchlorate, silver tetraborate, silver acetate, silver
benzoate, silver lactate, silver citrate, silver oxalate, and mixtures thereof.
9. The composition according to claim 1, wherein the source of zinc ion
is selected from the group consisting of zinc sulfate, zinc chloride, zinc
nitrate, zinc bromide, zinc iodide, zinc borate, zinc fluoride, zinc acetate,
zinc citrate, zinc acetylacetonate, zinc formate, zinc lactate, zinc oxalate,
zinc salicylate, zinc laurate, zinc valerate, and mixtures thereof.
10.
The composition according to claim 1, wherein the crosslinkable polymer (d)
comprises a polysaccharide.
11. The composition according to claim 10,
wherein the polysaccharide is a chitosan compound selected from the group
consisting of chitosan, salts of chitosan with 1 to 18 carbon monocarboxylic
acids, polycarboxylic acids, or both, methyl chitosan, N-carboxymethylchitosan,
and mixtures thereof, and wherein the crosslinking agent is sulfuric acid.
12. The composition according to claim 11, wherein the chitosan compound
is selected from the group consisting of chitosan, chitosan acetate, chitosan
lactate, chitosan glutamate, methyl-chitosan, N-carboxymethylchitosan, and
mixtures thereof.
13. The composition according to claim 12, wherein the
chitosan is at least partially in the form of chitosan-gel.
14. The
composition according to claim 13, wherein the chitosan compound is a mixture of
chitosan lactate and chitosan-gel.
15. The composition according to
claim 14, wherein the source of copper ion is copper sulfate and the source of
zinc ion is zinc sulfate.
16. The composition according to claim 15,
wherein the source of silver ion is selected from the group consisting of silver
nitrate and silver sulfate.
17. The composition according to claim 16,
wherein the source of silver ion is silver nitrate.
18. The composition
according to claim 1, wherein the zinc to copper weight ratio is from about 1:1
to about 3:1.
19. The composition according to claim 18, wherein the
zinc to copper weight ratio is from about 2:1 to about 2.5:1.
20. The
composition according to claim 1, wherein the silver to copper weight ratio is
from about 0.25:1 to about 1:1.
21. The composition according to claim
20, wherein the silver to copper weight ratio is from about 0.5:1 to about
0.75:1.
22. The composition according to claim 1, wherein the sources of
copper, zinc, and silver ions are present in amounts that provide a zinc to
copper weight ratio of from about 2:1 to about 2.5:1 and a silver to copper
weight ratio of from about 0.5:1 to about 0.75:1, wherein both weight ratios are
calculated based upon elemental copper, zinc, and silver.
23. The
composition according to claim 1, wherein the crosslinkable polymer is present
in an amount that provides a ratio of polymer to copper, calculated as elemental
carbon and copper, of from about 0.06:1 to about 0.74:1.
24. The
composition according to claim 23, wherein the ratio of polymer to copper is
from about 0.1:1 to about 0.5:1.
25. The composition according to claim
24, wherein the ratio of polymer to copper is from about 0.2:1 to about 0.3:1.
26. A composition for treating water, formed by preparing a mixture
comprising:
(a) about 16 to about 32% by weight copper sulfate
(calculated as pentahydrate);
(b) about 0.6 to about 12.5% by weight
silver nitrate;
(c) about 17 to about 70% by weight zinc sulfate
(calculated as heptahydrate);
(d) about 1 to about 5% by weight chitosan
salt;
(e) about 3 to about 19% by weight chitosan-gel; and
(e)
about 0.02 to about 0.05% by weight sulfuric acid.
27. The composition
according to claim 26, comprising:
(a) about 19 to about 26% by weight
copper sulfate (calculated as pentahydrate);
(b) about 2 to about 9% by
weight silver nitrate;
(c) about 40 to about 67% by weight zinc sulfate
(calculated as heptahydrate);
(d) about 2 to about 4% by weight chitosan
salt;
(e) about 5 to about 9% by weight chitosan-gel; and
(f)
about 0.03 to about 0.04% by weight sulfuric acid.
28. The composition
according to claim 27, comprising:
(a) about 21 to about 24% by weight
copper sulfate (calculated as pentahydrate);
(b) about 4 to about 7% by
weight silver nitrate;
(c) about 55 to about 65% by weight zinc sulfate
(calculated as heptahydrate);
(d) about 2 to about 3% by weight chitosan
salt;
(e) about 6 to about 8% by weight chitosan-gel; and
(f)
about 0.04% by weight sulfuric acid.
29. The composition according to
claim 26, wherein the chitosan salt is chitosan lactate.
30. The
composition according to claim 26, wherein the chitosan-gel is prepared by
dissolving 4% by weight chitosan powder into a 10% by weight solution of a weak
acid.
31. The composition according to claim 30, wherein the weak acid
is selected from the group consisting of citric acid, acetic acid, lactic acid,
boric acid, and salicylic acid.
32. The composition according to claim
31, wherein the weak acid is citric acid.
33. A solid water treatment
composition comprising:
(a) a matrix of soluble crosslinked polymer; and
(b) disposed within the matrix water soluble treatment materials
comprising:
(1) a source of water soluble copper in an amount that
provides a copper concentration in the water to be treated of about 0.2 ppm or
less;
(2) a source of water soluble silver; and
(3) a source of
water soluble zinc;
wherein the source of copper ion, the source of
silver ion, and the source of zinc ion are present in amounts that provide a
ratio of zinc ion source to copper ion source ranging from about 0.5:1 to about
4:1 and a ratio of silver ion source to copper ion source ranging from about
0.05:1 to about 2:1.
34. The composition according o claim 33, wherein
the crosslinked polymer comprises a crosslinked polysaccharide.
35. The
composition according to claim 34, wherein the crosslinked polysaccharide
comprises crosslinked chitosan.
36. The composition according to claim
35, wherein the chitosan is at least partially crosslinked with sulfate anion
moieties.
37. The composition according to claim 33, wherein the source
of water soluble copper comprises copper sulfate.
38. The composition
according to claim 33, wherein the source of water soluble zinc comprises zinc
sulfate.
39. The composition according to claim 33, wherein the source
of water soluble silver comprises silver nitrate.
40. The composition
according to claim 33, which is in the form of tablets, pellets, sticks or one
or more monoliths.
41. A solid water treatment composition comprising:
(a) a matrix of sulfur-crosslinked chitosan; and
(b) disposed
within the matrix:
(1) copper sulfate in an amount that provides a
copper concentration in water to be treated of about 0.2 ppm or less.
(2) silver nitrate; and
(3) zinc sulfate; wherein the copper
sulfate, silver nitrate, and zinc sulfate are present in amounts that provide a
ratio of zinc sulfate to copper sulfate ranging from about 0.5:1 to about 4:1
and a ratio of silver nitrate to copper sulfate ranging from about 0.05:1 to
about 2:1.
42. A method for treating bodies of water, comprising
contacting the water with the composition according to claim 1 for a sufficient
time to dissolve sufficient copper ion source, sufficient silver ion source, and
sufficient zinc ion source to provide copper, silver, and zinc ion
concentrations in the water sufficient to prevent or inhibit the growth of
microorganisms and to decrease the turbidity of the water.
43. The
method according to claim 42, wherein the water is swimming pool,
hot tub, spa, fountain, pond, cooling system, or humidification system water.
44. A method for treating bodies of water, comprising contacting the
water with the composition according to claim 33, for a sufficient time to
control or inhibit the growth of micro organisms and to decrease the turbidity
of the water.
45. The method according to claim 44, wherein the water is
swimming pool, hot tub, spa, foutain, pond, cooling system, or
humidification system water.
46. A composition for treating water,
formed by preparing a mixture comprising:
(a) a source of copper ion,
wherein the source of copper ion is present in an amount that provides a copper
concentration in the water to be treated of about 0.2 ppm or less;
(b) a
source of silver ion; and
(c) a source of zinc ion;
wherein the
source of copper ion, the source of silver ion, and the source of zinc ion are
present in amounts that provide a ratio of zinc ion source to copper ion source
ranging from about 0.5:1 to about 4:1 and a ratio of silver ion source to copper
ion source ranging from about 0.05:1 to about 2:1.
Description
FIELD OF THE INVENTION
The present invention relates to a
composition, water treatment system, and method for treating bodies of water to
inhibit microbial, algal, and fungal growth. In. particular the present
invention relates to the treatment of recirculating bodies of water, such as
swimming pools, hot tubs, spas, fountains, ponds, cooling system water, and
water contained in humidification systems, to inhibit, reduce or prevent the
growth of microorganisms such as bacteria, algae, fungi, and viruses. More
particularly, the invention relates to a metal salt-based composition for
maintaining swimming pool, spa, hot tub, or other water in a
pathogen-free and aesthetically acceptable state at reduced chlorine levels,
while simultaneously reducing both the formation of stains on pool surfaces and
the turbidity of water. However, the invention is also applicable to any body of
water, whether for industrial, agricultural, or recreational use, that is
subject to the growth of microorganisms.
DESCRIPTION OF BACKGROUND AND
RELATED ART
Bodies of water, and in particular those bodies of water
that are recirculated, provide fertile breeding grounds for algae, bacteria,
viruses, fungi, and other pathogens if the water is left untreated. Microbial
contamination can create a variety of problems, ranging from aesthetic
unpleasantries, such as slimy green water, to serious health risks such as
fungal, bacterial, or viral infections.
Swimming pools and other
recirculating bodies of water used for recreational purposes, such as hot tubs
or spas, are particularly conducive to microbial growth, as users introduce new
pathogens as they bathe or swim.
Ponds, such as garden or fish ponds,
often desirably contain some microorganisms as nutrients for their inhabitants.
In some circumstances, however, growth of undesirable and even desirable
microorganisms can become uncontrolled, reducing the ability of the pond to
support other desirable organisms by increasing the pond's biological oxygen
demand or BOD. Industrial or agricultural ponds, used for storing water used in
manufacturing or agricultural applications, are also subject to uncontrolled
growth of microorganism that can form sufficient biomass to become entrained
with the water and interfere with the operation of industrial or agricultural
machinery or processes.
Recirculating water cooling systems, such as
natural draft cooling towers, recycle heated cooling water by contacting the
water with an unsaturated gas, such as air, thereby cooling the water by
evaporation, and can also be used to cool the air, which may then be used to
ventilate areas inhabited by humans or other animals. Microorganisms can be
introduced by the cooling surfaces of the device, or by the air that comes into
contact with the water. Their growth, if allowed to go unchecked, can result in
sufficiently dense masses of organic material to clog or foul water flow lines
and valves, contribute to rot or corrosion, and decrease cooling efficiency.
Similarly, humidification systems, where water is sprayed into warm,
unsaturated air to cause essentially adiabatic mass transfer of some of the
water to the air in the form of water vapor, can also result in transfer of
pathogenic microorganisms from the water to the air. Since this humidified air
is often intended for breathing by humans or other animals, the result can be
infection by the contaminants transferred to the air from the water.
While many of these microbial contaminants that can grow in untreated
water are harmless, others can be pathogenic and lead to outbreaks of infectious
disease. One of the most common waterborne disease is dermatitis, which can be
caused by an overgrowth of Pseudomonas aeruginosa bacteria. Other common
diseases that can result from pathogens in bathing or swimming water include
bacterial gastroenteritis, external otitis (swimmer's ear), candidia and tinea
pedis (athlete's foot). More serious illnesses, such as Legionella pneumophila
(Legionnaire's disease), may also spread through contaminated swimming pools and
spas, as well as through contact of contaminated cooling water with air used in
building ventilation systems.
Halogens, in particular chlorine and
bromine, have traditionally been used to combat microbial contamination of
swimming pools, hot tubs, spas, etc. As strong oxidizing agents, halogens are
effective in destroying and preventing the growth of a wide variety of
organisms. They can be utilized in a variety of forms, including chlorine gas,
liquid chlorine, and more typically chlorine- or hypochlorite-releasing agents.
Calcium hypochlorite, Ca(OCl).sub.2, is commonly used to treat public swimming
pools, and contains 70% available chlorine. Chlorinated isocyanurates, including
dichlor and trichlor and their salts, are commonly used to treat private
swimming pools. Alternatively, chlorine can be generated by electrolysis for use
in swimming pools. In combination with other measures designed to limit the
build-up of organic matter in pool water, a constant adequate level of available
chlorine of 1 to 3 ppm is generally required to maintain a pool in a
pathogen-free state.
The use of chlorine, hypochlorite, and chlorine-
and hypochlorite-generating water treatment chemicals (hereinafter referred to
as "chlorine"), and in particular pool, hot tub, and spa treatment chemicals,
presents numerous problems, however. Most notably, chlorine has been associated
with health risks ranging from mild skin and eye irritation to an increased
incidence of cancer. Chlorinated products, resulting from the reaction of
chlorine with organic matter present in pool water, are thought to produce these
adverse effects. In particular, chlorinated hydrocarbons, produced in pool water
and then ingested by bathers, are suspected carcinogens.
Other
disadvantages associated with the use of chlorine as a biocide relate to its
performance and cost. The biocidal activity of chlorine is very sensitive to the
environment in which it is used. Specifically, chlorine is only effective as a
biocide within a narrow pH range. Relatively small variations in pH, therefore,
can cause a loss of biocidal activity. Chlorine's sensitivity necessitates both
careful monitoring of pool water pH as well as the adoption of pH-corrective
measures to maintain the pH in a suitable range. Exposure to sunlight can also
effect biocidal activity, as sunlight destroys hypochlorous acid formed from the
hydrolysis of Cl.sub.2. This necessitates the addition of stabilizers to prevent
the loss of biocidal activity from this source. The use of a strong oxidizing
agent, such as chlorine, can also cause aesthetic problems, including bleaching
and discoloration of swimwear, greenish hair, etc. In addition, the increasing
cost of chlorine-based pool chemicals makes their use in large quantities less
favorable economically.
For these and other reasons, it is desirable to
reduce the quantity of chlorine needed and used to achieve an acceptably low
level of microorganisms in swimming pools, hot tubs, spas, etc. A variety of
compositions have been suggested for this purpose, including compositions
containing heavy metal ions such as copper, silver, zinc, and nickel. Metal ions
are known biocides, and have been provided as metal salt-based compositions for
the treatment of swimming pools and other bodies of water. In particular, water
soluble inorganic salts of copper, such as copper sulfate, copper nitrate, and
copper chloride, have been suggested for use as algaecides and/or bactericides
for the treatment of water.
The use of copper or copper ion sources,
however, presents several disadvantages. Copper ions react with naturally
occurring anions in alkaline or near-alkaline water, and precipitate as
insoluble salts of, e.g., carbonate, oxide, and/or hydroxide. Copper
precipitation is also sensitive to pH. Precipitation leads to a loss of biocidal
activity as the copper ions are no longer available in solution. Precipitation
also causes aesthetic problems including turbidity of water and the formation of
stains on surfaces, such as pool surfaces. Conventional wisdom has been that, at
copper levels sufficiently high to have a significant biocidal effect, it is
necessary to add complexing agents having ligands that coordinate with the
copper ion in order to shield the ion from the anions in solution thereby
keeping it from precipitating and available for biocidal action. See U.S. Pat.
No. 5,632,904. A variety of sequestering agents have been used to enhance the
stability of the copper ions in solution in this way. For example, EDTA
(ethylene diamine tetra acetic acid), citric acid, and salicylic acid are known
to stabilize copper ions in solution by sequestering them. However, these
sequestrants can be broken down in the presence of oxidizing agents such as
chlorine, which will generally still be necessary in some quantities despite the
use of metal biocides. In addition, sequestrants can bind metal ions so strongly
that the biocidal activity of the ions is inhibited. These factors render the
use of sequestrant-containing biocides complicated and difficult for the average
pool user.
In addition, copper salt biocides are more effective against
algae than against bacteria and other pathogens. In order to obtain significant
bactericidal activity from copper salt biocides, unreasonably high copper
concentrations are necessary. As a result, copper salt containing biocides are
generally suitable as algaecides, requiring the use of additional biocides to
control bacteria and other pathogens.
Preparation of copper-salt
biocides, including copper-salt biocides containing salts of other metal ions,
such as silver and zinc salts, has also proven problematic. Specifically, the
failure to adhere to an ordered sequence of additions in the preparation of
known copper, silver, and zinc biocides has produced uncontrollable frothing as
well as the formation of black deposits during formation or compounding of the
biocidal composition.
There is a need, therefore, to improve
compositions of this type, and particularly, to provide metal biocide
compositions for treating recirculating bodies of water that permit maintenance
of the water in a pathogen-free and aesthetically acceptable state at reduced
chlorine levels, while simultaneously reducing or eliminating the problems of
staining and turbidity that have become associated with the use of metal
biocides without the need for sequestrants, as discussed above.
It is,
therefore, an object of the present invention to provide an improved metal
salt-based composition for treating recirculated bodies of water to
simultaneously inhibit microbial and algal growth and to reduce, as a result of
the action of these combined metals, the amount of chlorine necessary to
maintain the water in a pathogen-free and aesthetically acceptable state.
It is another object of the present invention to provide a metal
salt-based composition for treating water that provides copper, zinc, and silver
ions in solution, but maintains copper as well a silver at concentration levels
below the levels that will result in staining of surfaces, such as pool
surfaces, that contact the water, and also reduces or eliminates turbidity of
the water, without requiring sequestration of the copper ions that are in
solution.
It is a further object of the present invention to provide a
composition that has a simple method of manufacture that eliminates the need for
any special order of addition, as well as the need for heating and/or cooling
steps or applying pressure and that does not result in frothing or black
deposits forming during manufacture.
It is a further object of the
present invention to produce a metal-salt based composition that quickly
provides and effectively maintains concentrations of metal ions that reduce,
control, limit, or inhibit the growth of microorganisms in water.
It is
a further object of the present invention to provide a water treatment
composition, a water treatment system containing the composition, and a method
for using the composition that is characterized by ease of handling, simplicity
of use, long lasting effects (in the sense that the biocidally active ions
remain present and active in the water for several months), and effectiveness at
producing clear, pathogen-free water in swimming pools, hot tubs, spas,
fountains, ponds, humidifiers, cooling systems, and any other applications when
microbial contaminants (e.g., bacteria, algae, fungi, viruses, etc.) are
problems.
It is a further object of the present invention to provide a
solid metal salt-based water treatment composition that can be easily solidified
without expansion or shrinkage, and that can be easily molded into different
shapes, such as tablets, sticks, or pellets, or stuffed into various holders,
such as tubes.
It is a further object of the present invention to
provide a metal salt based water treatment composition that reduces or
eliminates the need for commonly used added metal ion sequestrants in the water
(such as EDTA, citric acid, or high levels of ionic polymers, etc.), while
avoiding staining of the surfaces in contact with the water, and turbidity of
the water.
These and other objects and advantages, as well as the nature
and proper use of the invention, will be readily apparent to those skilled in
the art from the following description and claims.
SUMMARY OF THE
INVENTION
The objects and advantages described above are provided by the
present invention, which is directed to a novel composition for treating bodies
of water, in particular recirculating bodies of water, to kill, remove, or
inhibit the growth of microorganisms, including bacteria, fungi, algae, viruses,
and other microorganisms at reduced chlorine levels (i.e., at chlorine levels
below those needed to maintain an acceptable reduction of microorganism growth
when halogens, such as chlorine or hypochlorite, or compounds that produce
these, are used as the primary or sole biocide or sanitizers) and at copper
levels well below the threshold at which surface staining occurs in most
recreational or industrial waters. The composition is formed by mixing sources
of copper, silver, and zinc ions, and in one embodiment of the invention, one or
more crosslinkable polymers, and a crosslinking agent, such as sulfuric acid.
The zinc and silver ion sources are present in such quantities as to provide
sufficient zinc and silver ions to the water and to achieve an acceptable
biocidal result to permit reduction in the amount of copper ion required.
Specifically, copper is used at levels that are sufficiently low that copper
staining does not occur, yet an acceptable level of reduction in microorganism
growth is maintained in the water. In addition, the presence of this low level
of copper ion in solution eliminates the need for added sequestrants, since at
the copper concentrations made possible by the inclusion of zinc and silver,
copper staining will not occur, and sequestrants are unnecessary. Additional
components of the composition, e.g., the polymer matrix, such as crosslinked
chitosan, need not be present in amounts sufficient to provide any significant
sequestering or flocculating effect under existing water conditions, and may be
used in amounts below those at which any sequestering or flocculating effect is
measurable.
The composition, water treatment system, and method of
treating water are discussed in more detail below by reference to swimming
pool water, however it will be understood that these can be used
advantageously in hot tubs, spas, ponds, water cooling systems, humidification
systems, and in any water system where microorganism growth is desirably
controlled. Accordingly, the discussion below is applicable to these systems as
well. In particular, the invention can be used advantageously in systems using
recirculated water and in particular in systems where the amount of oxidizing
biocide, like chlorine or hypochlorite, is desirably controlled or limited and
where staining by copper biocides may also cause problems.
This combined
effect of silver ions and zinc ions in permitting a reduction of the copper and
chlorine levels is unexpected, and is used in the present invention to provide a
biocidally effective composition that advantageously avoids the staining of
surfaces that contact the water, but not by adding large quantities of organic
sequestrants, which can later be broken down by the strong oxidizing agents in
the water, requiring constant replenishment (which generally is accomplished by
adding additional sequestrant complexed with yet more copper ion). Instead, the
present invention makes use of the surprising effect of silver and zinc ions, in
conjunction with copper ions, in maintaining a high degree of biocidal
effectiveness, particularly algaecidal effectiveness and bactericidal
effectiveness, despite substantially decreased copper ion concentrations. This
allows the copper ion concentration in the water to be maintained at a
sufficiently low level that precipitation is minimized or eliminated entirely,
and in any case, staining is avoided. Accordingly, the composition of the
present invention provides a metal salt-based biocide that represents a
significant advance over what has previously been available in the art. One
significant advantage of the present invention is that it provides effective
destruction and/or growth inhibition of both bacteria and algae, and is not
limited in its effectiveness to one or the other.
As indicated above,
the relative abundance of zinc ion source and silver ion source allow the use of
an amount of copper ion source significantly lower than would have been thought
to be required, and provides good bactericidal and algaecidal control while
still reducing staining. The ratio of zinc ion source to copper ion source (by
weight based on zinc and copper atoms) can range from about 0.5:1 to about 4:1.
The ratio of silver ion source to copper ion source (by weight based on silver
and copper atoms) can range from about 0.05:1 to about 2:1. As an example, a
ratio of zinc ion source to copper ion source of 2.3:1 and a ratio of silver ion
source to copper ion source of 0.6:1 have been found to be suitable.
In
an embodiment of the invention where the composition is provided as a solid
mixture of the metal ion sources and a soluble polymer matrix, the composition
is formed by mixing sources of the various metal ions, adding one or more
crosslinkable polymers, and as a final step, adding a crosslinking agent. The
resulting composition may then be formed in any desired shape, and dried to a
solid at room temperature using known methods of molding, extrusion, etc. The
composition solidifies upon drying without shrinkage or expansion of the solid.
Advantageously, the method requires no particular order of addition of the metal
ion sources, and no subsequent heating, cooling, or pressing steps. Accordingly,
the composition of the present invention is much simpler to prepare than
existing metal salt-based biocides and may be, for example, placed into a
suitable delivery container, such as a pipe, while still having a paste-like
consistency and then solidified without significant expansion or shrinkage. The
polymer matrix can be chosen to cause and accelerate the solidification of the
composition, and to provide the desired dissolution rate when the composition is
introduced into the water to be treated. The present invention achieves several
significant advantages in this respect. It is easily solidified to a form that
does not easily crumble or fall apart without the need for application of
external pressure, e.g., in pelletizing or tableting steps. In addition, the
crosslinked nature of the polymer matrix permits the material to dissolve in a
relatively short period of time, rather than immediately, or over several
months.
The present invention is also directed to a method for using the
composition by contacting the composition with water in which microorganism
growth is to be controlled. The composition is maintained in contact with the
water for a sufficient time to dissolve the copper, silver, and zinc ion sources
to the concentration needed to prevent or inhibit the growth of microorganisms.
When the metal ion sources are immobilized in a crosslinked polymer matrix, such
as chitosan or other polysaccharide, this matrix also dissolves in the water
(although at a rate that is likely to be different from, and slower than, the
dissolution rate of the ion sources) to obtain a concentration of dissolved
polymer that helps to decrease the water's turbidity. This method can be used to
treat, for example, water in swimming pools, hot tubs, spas, fountains, ponds,
cooling systems, and humidification systems. The present invention is also
directed to a water treatment system, which comprises the composition and a
container that immobilizes the composition while allowing it to come into
contact with the water to be treated. The container can be made from a variety
of materials, and can assume a variety of forms, provided that water is
permitted to flow in and out of the container and come into contact with the
composition.
The primary purpose of the polymeric matrix is to provide a
support for the metal ion sources, and to some extent to regulate their
dissolution rate over a relatively short period of time, rather than to maintain
the copper ion activity by sequestering it. As a result, there is no requirement
to use an amount of polymer that dissolves to provide an aqueous concentration
sufficient to sequester even a significant portion of the copper in solution. As
an example, the ratio of crosslinkable polymer material to copper, calculated as
elemental carbon and copper, can range from about 0.06:1 to about 0.74:1, more
particularly from about 0.1:1 to about 0.5:1, even more particularly from about
0.2:1 to about 0.3:1.
As previously indicated, the present invention
provides a number of advantages relative to current biocide compositions for the
treatment of recirculating bodies of water, including inhibition of microbial
and algal growth at reduced chlorine and copper levels. In contrast to known
compositions, the present invention achieves a biocidal result using levels of
copper below that at which staining occurs in normal recreational or industrial
water systems. As a result, the present invention achieves a biocidal effect
without staining surfaces in contact with the water, such as pool surfaces, and
without increasing the turbidity of the water. Moreover, the present invention
is prepared using a simple process which requires no special order of addition,
no specific heating and/or cooling steps, and does not cause frothing or the
formation of black deposits. The present invention is valuable in the control of
microbial and algal contamination of swimming pools, and more generally,
recirculating bodies of water. It provides a safe and economical alternative to
the use of known metal salt-based biocides, while reducing the need for chlorine
as a sanitizer.
DETAILED DESCRIPTION OF THE INVENTION
As
previously indicated, the present invention is directed to an improved
composition, water treatment system, and method for treating bodies of water to
inhibit, or reduce the growth of microbes, algae, and/or fungi at reduced
chlorine levels without noticeable staining. The composition is prepared by
combining metal ion sources, including sources of copper, silver, and zinc ions,
optionally with one or more crosslinkable polymers and a crosslinking agent. The
presence of zinc and silver ion sources maintains an acceptable biocidal effect
even in the presence of decreased amounts of copper and chlorine or
hypochlorite. This reduces the risk of the formation of stains on surfaces in
contact with water, and avoids turbidity of the water. The crosslinkable polymer
and the crosslinking agent are selected so that, when crosslinked, the resulting
composition releases ions into solution over a time period ranging from a few
hours to several days to a year, and the resulting polymer matrix used to
support the metal ion sources also dissolves to clarify the water. The invention
is prepared by mixing the various components, forming the resulting composition
into various shapes, and drying.
In more particular embodiments of the
present invention, the copper ion source is employed in an amount, in percentage
by weight based upon the total composition, ranging from about 16% to about 32%.
In particular, the composition can comprise about 19% to about 26% copper ion
source, more particularly, about 21% to about 24% copper ion source. The precise
amount that is appropriate is dependent to some extent upon the source of the
copper ion and its solubility in the water to be treated, but is significantly
below the amount necessary to provide the same biocidal effect in the absence of
silver or zinc ions. As discussed in more detail below, conventional copper-only
biocides yield a copper ion concentration in typical swimming pool
water of 0.5 to 1.0 ppm. Using the composition of the present invention (having
an amount of copper ion source in the ranges above and having silver ion source
and zinc ion source amounts as indicated below, and used in an amount of about
95 g/10000 gallons of water) provides an initial copper ion concentration of
about 0.15 ppm or less, which decreases to a long term concentration of about
0.07 to 0.1 ppm over several days. Copper ion can be provided by any suitable
copper-containing material known to yield copper ions in aqueous solutions at
the expected temperature and pH of the water to be treated. In one aspect of the
present invention, the source of copper ion is a soluble salt, such as copper
sulfate, copper chloride, copper nitrate, copper bromide, copper fluoride,
copper metaborate, copper ammonium carbonate, copper ammonium
sulfate, copper oxalate, copper salicylate, copper acetate, copper
formate, copper gluconate, or mixtures of these with each other or with other
copper salts. The copper can also be present in its elemental form, in which
case it enters the water by electrochemical reaction. Desirably, the source of
copper ion is copper sulfate, as the sulfate anion can contribute to the
polymerization or crosslinking of the monomer or crosslinkable polymer,
respectively.
In a more particular embodiment of the present invention,
the zinc ion source is employed in an amount, in percentage by weight based on
the total composition, ranging from about 17% to about 70%. In particular, the
composition can comprise an amount of zinc ion that can range from about 40% to
about 67%, more particularly from about 55% to about 65%. The appropriate amount
is dependent upon the source of zinc ion and its solubility in the water to be
treated. The zinc ion source is typically used in an amount that provides an
initial zinc ion concentration in the water to be treated of about 0.5 to about
0.6 ppm, which may decrease to a long term concentration of about 0.4 to about
0.45 ppm. Zinc ion can be provided by any compound known to yield zinc ions in
aqueous solution at the expected pH and temperature of the water to be treated.
In one aspect of the present invention, the source of zinc ion is a soluble
salt, such as zinc sulfate (heptahydrate or monohydrate), zinc chloride, zinc
nitrate, zinc bromide, zinc iodide, zinc borate, zinc fluoride, zinc acetate,
zinc citrate, zinc acetylacetonate, zinc formate, zinc lactate, zinc oxalate,
zinc salicylate, zinc laurate, zinc valerate, or mixtures of these with each
other or with other zinc salts. The zinc can also be provided in its elemental
form, in which case zinc ion enters the water by electrochemical reaction.
Desirably, the source of zinc ions is zinc sulfate, as the sulfate anion can
contribute to the polymerization or crosslinking of the polymer monomer or
crosslinkable polymer, respectively.
In a more particular embodiment of
the present invention, the silver ion source is used in an amount, in percentage
by weight based upon the total composition, ranging from about 0.6% to about
12.5%. In a particular embodiment the composition of the present invention can
comprise an amount of silver ion source in the range from about 2% to about 9%,
more particularly from about 4% to about 7%. The appropriate amount is
determined by the particular source of silver and its solubility in the water to
be treated. The silver ion source can typically be used in an amount that
provides a silver ion concentration in the water to be treated of about 0.3 to
about 0.4 ppm initially, which decreases over time to about 0.01 to about 0.02
ppm. Silver ion can be provided by any suitable silver-containing compound that
releases silver ions in aqueous solution at the expected pH and temperature of
the water to be treated. In one aspect of the present invention, the source of
silver ions is a soluble salt, such as silver nitrate, silver sulfate, silver
fluoride, silver chlorate, silver perchlorate, silver tetraborate, silver
acetate, silver benzoate, silver lactate, silver citrate, silver oxalate, or
mixtures of these salts with each other or other silver salts. Silver can be
provided as a single metal salt or a mixed metal salt composition. Silver can
also be provided in its elemental form, where the silver ion enters the water by
electrochemical reaction and/or dissolution of silver oxide. Desirably, the
source of silver ion is silver nitrate or silver sulfate, more particularly
silver nitrate, due to its favorable solubility.
In order to provide an
appropriate level of ions to the water over an appropriate time period, it is
desirable to combine copper sulfate, zinc sulfate, and silver nitrate as the
respective ion sources in amounts within the ranges discussed above. As
discussed above, the weight ratio of zinc ion source to copper ion source in the
composition, calculated as elemental copper and zinc, can range from about 0.5:1
to about 4:1, more particularly from about 1:1 to about 3:1, even more
particularly from about 2:1 to about 2.5:1. The weight ratio of silver ion
source to copper ion source in the composition, calculated as elemental copper
and zinc, can range from about 0.05:1 to about 2:1, more particularly from about
0.25:1 to about 1:1, even more particularly from about 0.5 1 to about 0.75:1.
The compositions according to the present invention are prepared by
combining the metal ion sources discussed above with one or more crosslinkable
polymers, which can then be crosslinked. The resulting polymer is temporarily
crosslinked by anionic bridges, and forms a three-dimensional network or matrix
that supports the metal ion sources, and immobilizes them to a certain extent,
while allowing them to slowly dissolve into the water to be treated. In
addition, the polymer matrix itself can clarify the water. While not wishing to
be bound by any theory, it is believed that the polymer matrix, which desirably
contains cationic moieties thereon, dissolves into the water over a period of a
few days to a year, depending upon the amount of polymer added to the water. In
quantities used in most swimming pool, hot tub, and spa
applications, the composition is generally completely dissolved in well under
three days in the water, and generally dissolves in a few hours. It is believed
that the cationic moieties of the dissolved polymer molecules electrostatically
attract and agglomerate colloidal and suspended particles in the water that
individually are sufficiently small to avoid settling by precipitation and
becoming trapped by the pool filter. These particles combine with the dissolved
polymer to form agglomerates of sufficient size to be trapped by the pool
filter, clarifying the water. Neither the dissolved polymer matrix nor the
copper ion of the present invention are believed to be present in sufficiently
high concentrations for the polymer to sequester significant amounts of copper
ions.
The crosslinkable polymers are added to the composition in an
amount ranging from about 4% to about 24% by weight based on the total
composition. More particularly, the monomers or crosslinkable polymers may be
added in an amount ranging from about 7% to about 13%, more particularly from
about 8% to about 11% by weight. In one aspect of the invention, a crosslinkable
polymer is used that comprises a chitosan compound, such as chitosan itself
(which is a deacetylated chitin (a naturally occurring biopolymer) that is
typically more than about 50% deacetylated), salts of chitosan, chitosan-gel, or
mixtures of these. Mixtures of chitosan salt powders with chitosan salt gels
have been found to provide good molding and casting properties to the resulting
composition.
Other polymers suitable for forming the matrix of the solid
composition according to the present invention include generally polymers that
will solubilize in water relatively quickly, that contain amine moieties when
dissolved in water, and that will form a solid when combined with the amounts of
silver, copper, and zinc ion sources described above. Desirably, these polymers
will not exhibit substantial expansion or shrinkage when combined with the above
ion sources and dried to form a solid. Examples of suitable polymers include
polysaccharides, including salts and derivatives of chitosan, such as chitosan
acetate, chitosan lactate, chitosan glutamate, methyl-chitosan,
N-carboxymethylchitosan, etc.
Desirably, a crosslinkable polymer is used
that is a mixture of a chitosan salt and chitosan gel. The chitosan salt is
desirably an easily prepared salt of chitosan, such as a salt of chitosan with a
1 to 18 carbon mono-or polycarboxylic acid, preferably chitosan acetate or
chitosan lactate. Chitosan materials, including chitosan and chitosan salts, are
commercially available from companies like Vanson, Aldrich, etc. The molecular
weights of chitosans suitable for use in the present invention typically range
from 5,000 to about 5,000,000. The level of deacetylation of the chitosan is
generally not critical to the claimed invention, and chitosan of any degree of
deacetylation available on the market can generally be used. However, chitosans
having degrees of deacetylation above 50% are suitable due to their solubility
characteristics. Salts of chitosan and lactic acid have been found to be
effective as the crosslinkable polymer. The chitosan salt is typically added to
the composition as a powder in an amount ranging from about 1% to about 5%, more
particularly from about 2% to about 4%, even more particularly from about 2% to
about 3%, by weight based on the total composition, and can be mixed with the
metal ion sources during manufacture of the composition.
The chitosan
can also be added in the form of a chitosan-gel, which can be added to the
composition after mixing of the chitosan powder with the metal ion sources.
Chitosan-gel is prepared by dissolving chitosan powder into a weak acid. Good
results have been obtained by dissolving 4% by weight chitosan powder into 10%
by weight of a weak acid, which may be citric acid, acetic acid, lactic acid,
boric acid, or salicylic acid, especially citric acid.
The inclusion of
both chitosan salt and chitosan-gel makes manufacture of the material
significantly easier and contributes to the clarity of the water treated with
the composition, as both function as water clarifiers. Specifically,
chitosan-gel provides moisture to the composition that allows formation of a
paste during manufacture, thereby allowing the composition to be easily extruded
and/or formed into a variety of shapes, such as monoliths, pellets, tablets, or
sticks. In addition, the chitosan-gel acts as a binder, which permits the
composition to solidify. Chitosan salt powder provides additional chitosan to
the composition while preventing it from getting too wet during manufacture. As
a result, chitosan salt powder and chitosan-gel are advantageously used in
combination, as described above. Specifically, chitosan powder alone may not
produce sufficient binding of the composition, and the use of chitosan-gel alone
may not allow the composition to dry to a solid when chitosan-gel is added at
the level needed to act as a water clarifier.
The crosslinking agent
added will depend upon the nature of the crosslinkable polymer used.
For
example, when a chitosan polymer is used as described above, sulfuric acid is
desirably employed in the composition as the crosslinking agent, and is
typically added in an amount ranging from about 0.02% to about 0.05% by weight,
based upon the total composition. The sulfuric acid aids the crosslinking of the
chitosan and helps to solidify the composition. While not wishing to be bound by
any theory, it is believed that crosslinking sulfate anions originating from
sulfuric acid and sulfate salt sources make bridges between amino groups of
chitosan polymeric chains. Combination of borate and phosphate anions can also
be used, although phosphates are not desirable in a swimming pool
environment, since they can promote formation of algae. Carboxyl methyl-chitosan
can be crosslinked with glutamic or aspartic acids or salts thereof
The
composition of the present invention is prepared by mixing the solid metal ion
sources, including copper, silver, zinc ion sources, and any solid monomer or
crosslinkable polymer, such as chitosan lactate, in powdered form in the
appropriate amounts to form a homogeneous blend. For instance copper sulfate can
be added in an amount of 16-32%, more particularly 19-26%, more particularly
21-24%, by weight (calculated as pentahydrate) based on the final composition.
Silver nitrate can then be added in an amount of 0.6-12.5%, more particularly
2-9%, more particularly 4-7% by weight based on the final composition. Zinc
sulfate can be added in an amount of 17-70%, more particularly 40-67%, more
particularly 55-65% by weight (calculated as heptahydrate) based on the final
composition.
As previously indicated, these materials can be added in
any order. If powdered monomer or crosslinkable polymer is to be used, it can
also be added at this point. For example, 1-5%, more particularly 2-4%, more
particularly 2-3% chitosan lactate can be added to the above metal salts. These
materials can then be blended to form a homogeneous blend using known and
readily available mixing equipment and techniques, such as Mixmullers, Hobart
mixers, and the like.
When chitosan lactate powder is used (i.e.,
chitosan is the crosslinkable polymer) chitosan-gel, prepared by dissolving
chitosan powder into a weak acid, is then added to the blend. Chitosan-gel that
has been prepared by dissolving 4% chitosan powder into 10% weak acid, such as
citric acid, has been found to be suitable. However, as mentioned above, other
weak acids, such as acetic acid, lactic acid, boric acid, and salicylic acid can
be used. After addition of the crosslinkable polymer, any necessary crosslinking
agents are added. When chitosan lactate and/or chitosan-gel are added as the
crosslinkable polymers, sulfuric acid is used as the crosslinking agent.
However, any crosslinking agent suitable for crosslinking the polymer used can
be added. The resulting paste is then formed into the desired shape. For
example, the composition can be cast in the form of tablets, pellets, granules,
extrudates, or a monolith. The composition is then permitted to dry to a solid
at room temperature and ambient humidity. Advantageously, no significant
expansion or contraction in volume occurs during this process.
This
simple preparation process results in a water treatment composition comprising a
combination of metal salts disposed within a matrix of cross-linked polymers.
The matrix is formed by polymerization of one or more monomers, followed by
crosslinking, or by crosslinking of the crosslinkable polymer by the
crosslinking agent. For instance, when the crosslinkable polymer is chitosan,
the sulfate anions of both the zinc and copper sulfate salts, as well as
sulfuric acid, contribute to the crosslinking. When placed in contact with
water, metal ions comprising the present invention are leached from the
composition over time. Components of the composition that are more slowly
soluble, like the crosslinked chitosan, or that are relatively insoluble, are
also released into the water, acting as water clarifiers. Chitosan and
chitosan-gel are both effective water clarifiers, as discussed above. The
preparation process is conducted under ambient temperature and pressure
conditions, and no special precautions need to be taken.
In one aspect
of the present invention, the composition is provided in conjunction with a
container to form a water treatment system. The container can assume a variety
of forms, provided that at least one water inlet opening and one outlet opening
are present. The container may be simply a pipe having the solid composition
disposed inside, with open ends, and optionally with some means for keeping the
solid composition relatively immobilized within the pipe. For instance, the
water treatment system may contain one or more screens, mesh, baskets, webs or
baffles that prevents large particles or pieces of the composition from passing
through, and keeps them within the pipe. In another embodiment, the container
may in the form of a basket made of plastic or metal mesh, in particular molded
plastic mesh. The mesh contains a plurality of openings of sufficient size to
allow water to freely flow into and out of the basket, and thus come into
contact with the composition inside, but to prevent large particles of the
composition from leaving the basket. In one aspect of the invention, the closed
basket is of a shape and size suitable for insertion into a swimming
pool skimmer trap or leaf trap, or attachable to a cleaner moving about
the pool.
In the practice of the present invention, the composition can
be used to treat bodies of water, in particular recirculating bodies of water to
inhibit microbial growth. Specifically, the composition can be used to treat
swimming pools, hot tubs, spas, ponds, cooling water systems, humidification
systems, fountains, etc. The composition and/or the water treatment system
containing it, is desirably placed in the water in a way that will maximize the
amount of water that comes into contact with the composition. For instance, the
composition can be placed in the water in such a way that forced or natural
currents or flow of the water brings water into contact with the composition. In
a swimming pool, hot tub, or spa, this can be accomplished by
placing the composition or water treatment system in the skimmer trap. An
alternative is to place the composition or water treatment system near a pump
outlet, so that recirculated water is continuously discharged near the
composition and comes into contact with it. However, adequate results can be
obtained by simply placing the water treatment system into the body of water and
allowing it to move around in the water with any currents that exist. The solid
composition is generally added in an amount of 95 g/10000 gallons of pool water.
This will maintain an acceptable level of biocidal activity for 3 to 12 months.
While not wishing to be bound by any theory, it is believed that the
composition of the present invention functions by allowing metal ion sources,
which are soluble in water and are typically water soluble salts of the metal
ion, to dissolve relatively quickly. The crosslinked polymer forms a structural
matrix for supporting these salts, and regulates their dissolution to some
extent. As time passes and embedded particles of salt near the surface of the
solid dissolve, the structural polymer matrix becomes more porous, allowing
water to access and dissolve particles of metal salts located within the solid
material.
The use of the present invention does not require that the
operation of the pool, hot tub, spa, cooling system, fountain, etc. be
significantly modified, and normal water circulation rates, filtration, etc.
should be unaffected. However, the addition of water treatment chemicals, such
as chlorine or other halogen biocides, sequestrants, or copper biocides can be
decreased substantially by using the present invention. For instance, the
chlorine content of a typical swimming pool can be reduced to
below 1 ppm, typically to around 0.5 ppm, a significant reduction from the 1-3
ppm required using conventional treatment systems.
Moreover, the amount
of copper used in the composition of the present invention is significantly
reduced when compared to that required by conventionally available copper
biocides. For example, conventional copper-containing biocidal compositions for
use in swimming pools provide a copper ion concentration in the pool water of
0.5 to 1.0 ppm, well above the industry accepted staining threshold. By
contrast, the composition of the present invention generally provides an initial
copper ion concentration of around 0.2 ppm, and this drops to a long term
concentration (i.e., the concentration achieved after about 3 to 4 weeks of
contact with the water) of around 0.08 to around 0.1 ppm, well below the
accepted staining threshold. Without being bound by any theory, it is believed
that the zinc and silver ions together provide an increased biocidal activity
that decreases the need for copper ions. Because the zinc ion is nonstaining,
and the silver and copper ions are present in amounts below those at which
staining occurs, it is not necessary to add sequestering agents, such as EDTA,
to avoid staining and precipitation. This also helps to avoid excessive binding
of metal ions by the sequestrants and unexpected release of metal ions when the
sequestrants are broken down by oxidants in the water.
The invention can
be more clearly understood by reference to the following examples, which are not
to be construed as limiting the invention in any way.
EXAMPLES
Example 1
179.3 g of ZnSO.sub.4.7H.sub.2 O, 64.5 g of
CuSO.sub.4.5H.sub.2 O, 14.4 g of AgNO.sub.3, and 7.2 g of chitosan lactate
(Vanson) were mixed mechanically thoroughly. Chitosan gel was prepared by
thoroughly mixing 4 g of chitosan powder (Aldrich, high molecular weight) in 100
ml of a 10% citric acid solution and heating slightly until dissolved. 22.1 g of
this gel was mixed with the above metal salt/chitosan lactate mixture for a few
minutes and to form a paste. 0.5 g of 25% H.sub.2 SO.sub.4 was added to the
paste and mixed thoroughly. The paste was left to dry overnight at 40.degree. C.
The product solidified into a rigid mass that neither shrank nor expanded during
solidification. The resulting product was suitable for treating a 30,000 gallon
swimming pool.
Example 2
A paste was made
following the procedure described in Example 1, except that 191.2 g
ZnSO.sub.4.7H.sub.2 O, 69.1 g CuSO.sub.4.5H.sub.2 O, 15.4 g AgNO.sub.3, and 7.9
g of chitosan lact to make the initial salt mixture, to which was added 23.1 g
of the chitosan gel described above, and 0.4 g of 25% H.sub.2 SO.sub.4. 154 g of
this mixture was inserted into a short copper pipe and left to dry overnight at
room temperature. Again, the material dried without expansion or shrinkage. The
pipe containing the dried materials was placed into the skimmer basket of a
13,500 gallon swimming pool. By the end of three days in the pool
the materials were dissolved and the pipe was empty. The pool water remained
crystal clear, and the pool surfaces were not stained for more than 2.5 months
of an intensive swimming season, during which the free available chlorine level
was held below 1 ppm. The conditions of this pool water is shown in Table I
below.
______________________________________
FREE
AVAILABLE
DATE OF CHLORINE Cu Ag Zn
SAMPLING pH (PPM) (PPM) (PPM) (PPM)
______________________________________
6/10/97 (prior
7.29 0.99 0.021 <0.006
0.029
to treatment)
6/13/97 7.41 0.06 0.191 0.034 0.489
6/20/97 7.35 0.67 0.182 0.025 0.505
6/27/97 7.70 0.56 0.163 0.028 0.516
7/8/97 7.81 0.08 0.115 0.018 0.489
7/14/97 7.80 0.25 0.099 0.024 0.426
7/29/97 7.73 0.21 0.088 0.027 0.431
8/14/97 7.49 0.10 0.077 0.028 0.431
8/25/97 7.65 0.03 0.079 0.019 0.415
______________________________________
While the invention has been described in detail in the above
description, this should construed as limiting the invention, and other
modifications and embodiments within irit of the invention are intended to be
encompassed by the claims.
* * * * *
