Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1999-04-01
2001-05-01
Smith, Duane (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S764000, C210S765000
Reexamination Certificate
active
06224779
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and materials for inhibiting the growth of algae in swimming pools that use chlorine as a primary disinfectant.
BACKGROUND OF THE INVENTION
Growth of algae and pathogens in swimming pool water is almost universally controlled by free chlorine at concentrations of from 1 to 3 milligrams per liter (mg/L) at pH from 7.2 to 7.6; lower chlorine concentrations are marginally effective and higher chlorine concentrations are irritating to humans. Consumption of chlorine results in the formation of chloride ion. Chlorine concentration is maintained by adding elemental chlorine and/or chlorine-releasing chemicals to the water. Examples of the latter are sodium hypochlorite, calcium hypochlorite, and trichloro-s-triaizinetrione.
Algae may be controlled by chlorine alone (at pH 7.2 to 7.6) during periods of cold weather and low solar flux, but other compounds are needed to supplement the action of chlorine during periods of warm weather and high solar flux. Such compounds include n-alkyl dimethyl benzyl ammonium chlorides and/or ions of heavy metals such as copper, silver, zinc, tin, nickel and mercury. Monovalent silver ion would be particularly advantageous because it is effective at low concentrations and is harmless to humans; it is not widely used because it is difficult to dissolve silver ion into swimming pool water without precipitating silver chloride. Upon exposure to light, silver chloride precipitate decomposes to elemental silver, a black precipitate that imparts a haze to the water and discolors pool surfaces. On the other hand, aqueous solutions of silver chloride are light-stable.
The problem of dissolving of silver ion into pool water without precipitating silver chloride is well recognized. U.S. Pat. No. 5,149,354 discloses the reaction of soluble monovalent silver salts with sodium gluconate to form water-soluble complexes with silver, which do not readily react with chloride or sulfate in pool water to form silver precipitates. Complexed silver likewise does not readily inhibit algae and pathogens and supplementation with copper metal and cupric ion is mandated. In some instances the copper compounds are substantially the major ingredient in the formulation. U.S. Pat. Nos. 5,073,382, 5,078,902, 5,089,275, 5,098,582 and 5,223,149 disclose the use of divalent and/or trivalent silver ion. Still others (U.S. Pat. Nos. 4,337,136; 4,525,253; 4,680,114; 4,781,805) effect dissolution of silver by passing a controlled electric current across silver-containing electrodes in a cell through which water is passed. U.S. Pat. No. 4,931,078 discloses a procedure in which silver salts are incorporated into molten glass which, when cooled, releases silver ions into water at a rate controlled by the surface area and chemical composition of the solid glass particles.
SUMMARY OF THE INVENTION
I have discovered an improved method for inhibiting the growth of algae in swimming pools by introducing monovalent silver ion in a manner which avoids precipitating silver chloride in the main body of water in the pool. The method of my invention does not require the use of electric current, complexing with materials such as sodium gluconate, supplementation with other metals such as copper, or incorporation into glass.
The process of my invention is directed to inhibiting the growth of algae in a swimming pool system comprising a main body of water in the pool and a re-circulation system for removing a portion of water from the main body of water in the pool, passing the removed portion of water through a filter to produce filtered water and returning the filtered water to the main body of water in the pool. The filter element is located within a filter case, which shields the filter from light. In the typical operation of a fresh water swimming pool of this type, the main body in the pool will have a pH maintained in the range of from about 7.0 to about 7.8, a temperature in the range of from about 50° F. and up to about 110° F., and have chlorine in concentrations of from about 0.3 to about 5 milligrams per liter (mg/L). The chloride concentration of the water in the pool can vary over a wide range depending upon the rate of chlorine addition to the body of water in the pool and the length of time that chlorine has been added to the pool. Accordingly, the chloride concentration in such a pool can range from as low as about 25 up to about 10,000 mg/L.
Within the above ranges, the pH is usually in the range of from about 7.2 up to about 7.6 and water temperature will usually not be in excess of about 100° F. The chlorine concentration also tends to be at least about 1 mg/L and is usually not greater than about 3 mg/L.
In accordance with my inventive process, solid silver chloride is deposited on the filter and at least a portion thereof if not all, is subsequently dissolved into the filtered water, thus furnishing soluble silver chloride, and hence uncomplexed, monovalent silver ions, to the main body of water in the pool. The quantity of silver chloride deposited on the filter being in a quantity at least sufficient to provide a silver ion concentration in the body of water in the pool up to the saturation level of silver ions at the conditions existing in the body of water in the pool. Generally, two factors determine the saturation level. They are water temperature and chloride concentration of the water in the pool. Typically, in the practice of my invention, the silver ion concentration in the body of water in the pool will be maintained in the range of from about 0.01 to about 24 micrograms of silver per liter of water. This range will be understood by reference to Table 1, below. In general operation, the silver ion concentration will be at least about 0.1 and even 0.5 micrograms per liter of water. The silver ion concentration can also be as low as 15 or even 3 micrograms per liter of water. Any of these concentrations of monovalent silver ion are effective to inhibit algae growth, however, it is preferred to utilize higher concentrations of silver ions as the temperature of the water in the pool increases. It is also advantageous to maintain the silver ion concentration, in accordance with my invention, at or close to the saturation level for the conditions existent in the pool water, although saturation is not a requirement of my invention and lower levels of silver ion concentration in the pool are generally found effective.
My invention permits a means for dissolving silver chloride into swimming pool water with minimal or no precipitation of silver chloride in the main body of pool water. Furthermore, in accordance with my invention, the silver ion is not complexed and is, thus, effective at low concentrations without addition of other heavy metal ions.
The method of my invention calls for depositing finely divided silver chloride on the filter of a pool circulation system, whereupon part or all of the deposited silver chloride is subsequently dissolved into the filtered water (filtrate), which is returned to the main body of water in the pool. Silver chloride need not be introduced as such; it may be formed in situ by reaction of silver salts with chloride in the circulating water. Examples of such salts are salts of organic acids (such as silver acetate, silver lactate and silver propionate), silver chlorate, silver fluoride, silver fluosilicate, silver nitrate, and silver sulfate.
Another aspect of my invention is to package silver chloride or other silver salts and solutions of silver salts, more soluble in water than silver chloride, in ways that permit handling without contacting skin and pool surfaces. This is accomplished by packaging such silver salt solutions in disposable syringes and by packaging such silver salts into opaque plastic, glass, paper, metal foil, or gelatin containers. These silver salts can also be mixed with binders and compressed into pills or pellets. A particularly convenient way of introducing silver compounds is to incorporate them into pellets with chlorine-releasing chemicals, such as calcium hy
Hoey Betsey Morrison
Ryder Thomas G.
Smith Duane
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