Water must be effectively treated to remove or stop the growth of micro-organisms such as bacteria, parasites, or algae, particularly when the water is confined. Confined volumes of water are highly susceptible to rapid micro-organism growth and can become health hazards if not properly and regularly treated. Water purification can be accomplished by filtration or by treating the water with chlorine, bromine, ozone, or silver ions to provide water suitable for consumption or for use in recirculating systems such as swimming pools, hot tubs, spas, or cooling towers. For example, water can be treated with silver-containing materials described, for example, in U.S. Pat. No. 5,352,369 and in U.S. Ser. No. 08/628,405, entitled "Self-Regulating Water Purification Composition" and filed April 5, 1996, which are incorporated herein by reference.

In recent years, chlorine dioxide (Cl O2 (g)) has been used to disinfect drinking water. See, for example, C. Yapijakis "Rx for H2O" Water & Water Engineering, May (1978), p. 33-37 and "Chlorine Dioxide" in Handbook of Chlorination and Alternative Disinfectants, G.C. White, Van Nostrand Reinhold, New York (1992), Chapter 12, p. 980-1045. Chlorine dioxide can be generated in several different ways. For example, chlorine dioxide can be produced by introducing chlorine gas into the flowing stream containing chlorite (ClO2) or chlorate (Cl03-).

Chlorine dioxide also can be produced by lowering the pH of a concentrated solution of chlorite or chlorate. This can be done either directly in water or, as in certain methods of disinfecting bandaged wounds, by adding an acid (e.g., citric acid) and water to a dry powder containing salts of chlorite or chlorate, as described, for example, in Chvapil et al. U.S. Pat. No.5,104,660. Chlorine dioxide also can be generated by adding chlorine (HOC1) or exposing a catalyst to a solution containing chlorite. See, for example, Daly et al. U.S. Pat. No. 5,435,984.

Summarv of the Invention In one aspect, the invention features a method of purifying water including the step of contacting water containing an oxide of chlorine, such as chlorine dioxide, chlorite, or chlorate, with a water purification composition including a Group 11 or Group 12 metal, such as silver, copper, or zinc. Preferably, the water contains chlorite.

In preferred embodiments, the water has a pH between about 5 and 9.

More preferably, the water has a pH between 6 and 8. Most preferably, the water has a pH between 6.5 and 7.5.

Preferably, the water purification composition includes a silver- containing material, and the silver-containing material maintains a silver ion concentration in the water of between 0.01 and 0.1 ppm. The silver-containing material can include a second metal like zinc, copper, aluminum, iron, or manganese.

The silver-containing material may further include an inorganic oxide having a zeta potential less than or equal to +20 mV in the water being purified (e.g., alumina).

The water may further contain a peroxygen compound or a halogen.

Preferably, the peroxygen compound is a peroxymonosulfate such as potassium peroxymonosulfate.

The water may be recirculated, for example, in swimming pools, spas, cooling towers, or other industrial applications. Alternatively, the water can be single pass water, such as drinking water or waste water.

In another aspect, the invention features a method of purifying water including the steps of adding an oxide of chlorine (i.e., chlorine dioxide, chlorite, or chlorate) to water; and contacting the water with a water purification composition including a Group 11 or Group 12 metal (i.e., silver, copper, or zinc).

In yet another aspect, the invention features a method of purifying water including: (1) adding an oxide of chlorine to water; (2) adding a peroxygen compound or a halogen to the water; and (3) contacting the water with a water purification composition including a Group 11 or Group 12 metal.

The water purification composition can be a silver containing material.

Alternatively, the water purification composition can include copper or zinc. The

silver containing material can maintain a silver ion concentration in the water of between 0.01 and 0.1 ppm.

As used herein, "halogen" means free available chlorine or bromine in water. The halogen can be an active agent in the purification of the water.

As used herein, "purifying water" means killing bacteria, killing algae, killing cysts, destroying viruses, or stopping the growth of algae in water. Purifying water also can include destroying other parasites in the water.

The method is an effective way to treat and disinfect water. The method is economical and generally does not present significant carcinogenic and environmental threats. For example, the method can effectively destroy and kill bacteria, viruses, fungi, spores, cysts, or parasites in water, including Giardia, Cryptosporidium, or Legionella. The method of treating water also effectively controls levels of algae in the water.

Other advantages and features of the invention will be apparent from the detailed description, and from the claims.

Detailed Description Water can be purified by dissolving salts including chlorite (ClO2-) or chlorate (ClO3) in water at a concentration of up to 200 mg/L and adding Group 11 or 12 ions (e.g., silver (Ag+), copper, or zinc ions) to the water (e.g., at concentrations of up to 0.1 ppm, 2 ppm, or 5 ppm, respectively). Alternatively, chlorine dioxide gas (ClO2 (g)) can be dissolved in the water with the silver ions, copper ions, or zinc ions.

For example, the chlorine dioxide can be prepared independently and added to the water, or the chlorine dioxide can be generated from chlorite or chlorate in the water by adding an acid or other catalyst to the solution. Copper or zinc ions can be added to the water instead of or in addition to the silver ions.

The chlorite or chlorate can be the anion of any salt that is soluble in water at concentrations up to 200 mg/L. Preferably, the concentration of chlorite or chlorate is less than 50 mg/L. More preferably, the concentration of chlorite or chlorate is less than 20 mg/L. The chlorite or chlorate concentration is preferably

greater than 0.02 mg/L. Examples of suitable chlorite or chlorate salts include the lithium, sodium, potassium, calcium, magnesium, silver, copper, or zinc salts.

The silver ion concentration in the water can be produced by dissolving a silver salt in water or by exposing the water to a water purification composition that includes silver. Copper or zinc ions can be added to the water by exposing water to water purification materials that include copper, or zinc or by dissolving an appropriate salt in the water. The silver, copper, or zinc in the water purification material can be a metal or metal salt. For example, the water purification compositions described in U.S. Pat. No. 5,352,369 and in U.S. Ser. No. 08/628,405 are appropriate silver-containing materials for introducing silver ions into the water.

The silver-containing material can include silver metal on a support. The support can be a ceramic and can include an inorganic oxide, e.g., an aluminum oxide. The silver can be chemically deposited on the ceramic support or dispersed as a powder, shavings, or turnings with the ceramic support. The silver-containing material can include a second metal, preferably zinc, copper, aluminum, iron, or manganese, most preferably, zinc. Alternatively to the silver-containing material, the water purification composition can be a composition that introduces copper or zinc ions into the water.

The water purification composition can be in powder, granule, tablet, stick, monolithic ceramic foam, or any other suitable form.

The water can contain other oxidizing agents to enhance the purifying ability of the chlorite or chlorate and silver ions. The additional oxidizing agents include halogens, such as chlorine (e.g., trichloroisocyanurate or calcium hypochlorite) or bromine, and peroxygen compounds, such as potassium peroxymonosulfate or hydrogen peroxide. The preferred oxidizing agent is potassium peroxymonosulfate. Potassium peroxymonosulfate is a triple salt mixture of K2SO4KHSO4.2KHSOs (OXONETM, manufactured by E.I. duPont de Nemours and Company, Inc., Delaware). The oxidizing agent helps provide low level of chlorine dioxide to the water. Peroxymonopersulfate can also convert a halide (i.e., chloride or bromide) into a halogen (i.e., chlorine or bromine).

The water purified by the method has a pH that is nearly neutral (i.e., it is not particularly acidic or basic). Preferably, the pH of the water being purified is

between 5 and 9. More preferably, the pH of the water is between 6 and 8 and, most preferably, the pH is between 6.5 and 7.5.

The water purified according to the method can be single pass water, such as drinking water or waste water, or recirculated water, such as water in swimming pools, spas, cooling towers, or other industrial applications where a recirculating body of water is disinfected.

It is believed there is a synergy between silver ion and chlorine dioxide, chlorite, or chlorate. By adding silver ion to the water being treated prior to formation of chlorine dioxide, greater disinfecting ability can be imparted on both the chlorine dioxide generated in the water and the residual chlorite or chlorate dissolved in the water. Typically the silver ion concentration is not greater than 0.1 ppm.

Silver ions in combination with chlorite (or chlorate) in water are effective at killing bacteria, as shown in Examples 1-14. In addition, bactericidal activity of chlorite is enhanced when an oxidizing agent (i.e., peroxymonosulfate) is added to the water, as demonstrated in Examples 8-14. In particular, the combination of chlorite with silver ion and an oxidizing agent such as potassium peroxymonosulfate kills bacteria efficiently in water. The method of treating water by adding chlorite and silver ions to water is also suitable to control the growth of algae, as demonstrated in Examples 15-21.

The following Examples are to be construed as merely illustrative, and not limitive, of the-remainder of the disclosure.

Examples 1-7 Aqueous solutions of chlorite (ClO2-), chlorate (Cl03-) and silver ions (Ag+) were tested alone and in various combinations for their bactericidal efficacy against an inoculum of E. coli. Experiments were conducted in 500 mL of room temperature, double distilled, deionized water at pH 7.0 in acid-washed, pre-sterilized 1L Erlenmeyer flasks. The flasks were inoculated with approximately 2 x 106 colony forming units per mL (CFU/mL) of E. coli. 1 mL aliquots were taken after 20 minutes of contact time and neutralized with 0.01 mL of a solution containing 10% sodium thioglycolate and 14.6% sodium thiosulfate. The efficacy of this neutralizer was

determined to be 100% effective against the various agents tested. The results of the tests are summarized in Table 1. As demonstrated in Examples 5-7, silver ions in combination with chlorite or chlorate showed a bactericidal synergy against E. coli.

The bactericidal activity of the solutions containing, e.g., silver ions and chlorite was greater than the sum of the activities of each component alone. TABLE 1 Example System Log Reduction 1 C102 0 2 ClO; 0 3 C102- & C103- 0 4 Ag 1.19 5 Ag+ &ClO2 >4.0 6 Ag+ &C1O 2.11 7 Ag+, C102- & C103- >5.14 Concentrations were as follows: Ag+ = 0.05 ppm; Cl 02 = 5.0 ppm; ClO; = 0.2 ppm.

Examples 8-14 Additional experiments were performed with aqueous solutions of chlorite, silver ions, and potassium peroxymonosulfate (hereinafter MPS) in various combinations to determine the bactericidal activity of the components (i.e., low levels of chlorine dioxide in combination with silver ions) against E. cold. Experiments were conducted in 500 mL room temperature, double distilled, deionized water at pH 7.0 in acid-washed, pre-sterilized 1L Erlenmeyer flasks. The flasks were inoculated with approximately 2 x 106 CFU/mL of E. coli. 1 mL samples were taken after 10 minutes of contact time and neutralized with 0.01 mL of a solution containing 10% sodium thioglycolate and 14.6% sodium thiosulfate. The efficacy of this neutralizer was determined to be 100% effective against the various agents tested. Results of the experiments are summarized in Table 2. As the results of Examples 12-14 demonstrate, chlorite in combination with MPS or silver ion show a synergy in their bactericidal activity against E. coli.

TABLE2 Example System Log Reduction 8 MPS 0.46 9 Ag+ 0.26 10 ClO2 O 11 MPS&AG+ 0.38 12 Ag+ &C102 2.0 13 MPS & C102 2.47 14 MPS, Ag+, & ClO2² >5.2 Concentrations were as follows: MPS (as C12) = 4.5 ppm; Ag+ = 0.034 ppm; ClO²- = 4.8 ppm; C103 = 0.2 ppm.

Examples 15-17 The ability of silver ions, chlorite, and the combination of silver ions and chlorite to prevent the growth of the green alga Chlorella vulgaris was tested. The tests were carried out using 25 mL of sterile Allen's medium (329 mg K2HPO43H2O, 66 mg CaCl2*2H2O, 50 mg NH4Cl, 1000 mg NaNO3, 513 mg mgSO4e7H2O and 1 mL of 3,000 ppm FeCl3 solution in 1L distilled, deionized water) at room temperature in 50 mL acid washed, sterilized Erlenmeyer flasks. The pH of each solution was adjusted to 6.5-7.5 using 1N NaOH and 1N HNO3. The flasks containing the various test solutions were inoculated with approximately 5 x 105 cells/mL of the test alga and placed on an orbital shaker at 500 rpm under 200 ft-candles of illumination. After 96 hours the cells in a 10 pL aliquot from each flask were counted using a hemacytometer counting chamber and inhibition of growth relative to a control was calculated. Results are summarized in Table 3. The results of Example 17 indicate that silver ions with chlorite are synergistic in their algistatic activity against Chlorella vulgaris. TABLE 3 Example System Growth Inhibition (%) 15 Ag+ 26% 16 ClO2 10% 17 Ag+&ClO2- 100% * Concentrations were as follows: Ag+ = 0.05 ppm; Cl 02 = 5.0 ppm.

Examples 18-21 After 7 days under 200 ft-candles of illumination with shaking at 500 rpm, the Ag+ & C102 solution described in Example 17 above still showed 100% growth inhibition. This solution was filtered through a sterile, 0.45 clam, Teflon syringe filter into a sterile, acid washed, 50 mL borosilicate glass Erlenmeyer flask. The pH of the solution was checked and found to be between 6.5 and 7.5. The solution was re- inoculated with Chlorella vulgaris to a cell concentration of approximately 5xlOs cells/mL. The solution remained under 200 ft-candles of illumination on an orbital shaker at 500 rpm for 25 additional days. As Examples 18-21 illustrate, the algistatic activity of the Ag+/C1O2 solution is maintained over a period of at least 25 days, as suggested by the nearly constant concentration of cells in the sample (Table 4). TABLE4 Example Day Cells/mL 18 7 5.1x105 19 10 4.7x105 20 14 5.5x105 21 25 7.3x105 Examples 22-28 An experiment was performed to test the ability of Ag+, Cl O2 and MPS and combinations of these three to prevent the growth of the green alga Chlorella vulgar is. These tests were carried out using 25 mL of sterile CI - free Allen's medium (329 mg K2HPO4e7H2O, 1060 mg Ca(NO3)2H2O, 77 mg NH4NO3, 1000 mg NaNO3, 513 mg MgSO4.7H2O and 72 mL of a 100 ppm iron nitrate solution in 928 mL distilled, deionized water) at room temperature in 50 mL acid washed, sterilized Erlenmeyer flasks. The pH of each solution was adjusted to 6.5-7.5 using 1N NaOH and 1N MONO3. Flasks containing the various test solutions were inoculated with Chlorella vulgar is to a cell density of approximately 3x105 cells/mL and placed on an orbital shaker at 200 rpm under 200 ft-candles of illumination. After 96 hours, the cells in the 10 pL aliquot from each flask were counted using a hemacytometer

counting chamber and inhibition of growth relative to a control was calculated. In order to determine if the treatments were having an algistatic or algicidal effect, 1 mL of each solution was transferred aseptically to a 50 mL acid washed, sterilized Erlenmeyer flask containing 24 mL of sterile, Cl free Allen's medium and placed under 200 ft-candles of illumination on an orbital shaker at 200 rpm. After 10 days, the new flasks were examined for growth. If the new flasks showed growth, the cells had revived and the original solution was considered algistatic. If the new flasks showed no growth, the cells were dead and the original solution was considered algicidal. Results are shown in Table 5. Examples 22-24 illustrate that Ag+, ClO2 and MPS are all algistatic. Examples 25-28 show that combinations of Ag+, MPS and ClO2 are algicidal. TABLE 5 Example System Growth Growth in Algistatic/ Inhibition ~ Fresh Media Algicidal 22 Cl O2 25% Yes Algistat (mild) 23 Ag+ 98% Yes Algistat 24 MPS 93% Yes Algistat 25 Ag+ & MPS 100% No Algicide 26 Ag & C102 90% No Algicide 27 MPS & ClO²- 100% No Algicide 28 Ag+, MPS & 100% No Algicide ClQ Concentrations were as follows: Ag+=0.1 ppm; ClO2-=10 ppm; MPS=10 ppm.

Other embodiments are within the claims. For example, the water containing chlorite or chlorate can be exposed to a catalyst to generate chlorine dioxide in the water, enhancing the purifying power of the mixture.