Recreational and commercial water systems, as well as natural bodies of water, e.g., ponds, are subject to contamination from the presence and growth of microbes, e.g., algae, pathogenic bacteria and fungi. The sanitization of standing or recirculating water systems typically involves introducing a halogen or halogen-containing material, e.g., a hypohalite material, such as a hypochlorite or hypobromite material, into the water system so as to establish a desired level, e.g., a sanitizing amount, of free available halogen (“FAHal”), e.g., free available chlorine (“FAC”), within the water system. The presence of free available halogen serves to eradicate or control deleterious amounts of microbial species, e.g., pathogenic bacteria, algae, fungi, etc that are present in the water comprising the water system. Hypochlorous acid and hypobromous acid are oxidizing materials that can also remove nutrients from water to which they are added, thus providing indirect protection against microbial infestation. Sanitation of water contacted by humans and animals is required because exposure to unsanitized or inadequately sanitized water that contains deleterious amounts of pathogenic bacteria, viruses, protozoa, etc can lead to the development of infection or disease.
FAHal, e.g., FAC or bromine, can be established in an aqueous system by adding regularly a source of hypohalous acid, e.g., hypochlorous acid (HOCl) or hypochlorite anion (ClO−), or hypobromous acid (HOBr) or hypobromous anion (BrO−) to the water comprising the aqueous system. There are many hypohalite generating materials. Non-limiting examples of hypohalite generating materials include chlorine gas, alkali metal hypochlorites, e.g., sodium hypochlorite and lithium hypochlorite, alkaline earth metal hypochlorites, e.g., calcium hypochlorite, halogenated hydantoins, such as the chlorinated and brominated hydantoins, e.g., 1,3-dibromo-5,5-dimethylhydantoin, chlorinated isocyanuric acid and its alkali metal derivatives, such as trichloroisocyanuric acid (also known as tri-chloro-s-triazinetrione), dichloroisocyanuric acid, and the corresponding salts sodium and potassium dichloro-s-triazinetrione, the N-halo-2-oxazolidinones, such as 3-chloro-4,4-dimethyl-2-oxazolidinone, and N,N′-dihalo-2-imidazolidinones, such as 1,3-dichloro-4,4,5,5-tetramethyl-2-imidazolidinone.
Recreational bodies of water, e.g., swimming pools, hot tubs, spas, etc, typically are treated so as to contain a level of FAHal, e.g., FAC, of from 1 to 10, e.g., 1 to 4, parts per million parts of water (ppm), sometimes reported as milligrams per Liter (mg/L). FAC levels in recreational bodies of water are generally maintained at from 1 to 2 ppm. FAC levels of 1 ppm or less, e.g., 0.5 to 1 ppm, are commonly maintained in cooling water systems. Water having a FAHal, e.g., FAC, content in amounts of greater than 10 ppm (generally in the range of hundreds to thousands of mg/L) can be used to sanitize surfaces or articles to which it is applied, e.g., food, equipment and tables used for the processing of raw food or in the preparation of processed food products.
Hypohalous acid, e.g., hypochlorous acid, or hypohalite anion, e.g., hypochlorite anion, can be introduced into water systems by passing the water, or a portion thereof, through a container that contains a donor source of the hypohalous acid or hypohalite anion. Other means include introducing chlorine directly into the water or adding the hypohalous acid donor material directly to the body of water to be treated. A common donor source of hypochlorous acid or hypochlorite anion is calcium hypochlorite. Calcium hypochlorite, e.g., granular calcium hypochlorite, can be added directly to the water to be treated, or placed in a container in the form of granules or tablets. When water is brought into contact with the calcium hypochlorite in the container, the calcium hypochlorite dissolves, thereby forming an aqueous solution comprising hypochlorite anion. This solution may be mixed with a water supply, added to water to be sanitized, or used directly for the intended application.
In the case of a standing or recirculating body of water, e.g., swimming pools, periodic batch additions of higher levels of hypochlorite anion can be made to the body of water in addition to the relatively steady and lower level additions described previously. Such batch additions of higher levels of hypochlorite anion are commonly referred to as a “shock treatment” or as “super chlorination” and are made on a periodic basis, e.g., once a week or once a month. Typically, the purpose of a shock treatment is to briefly increase the FAC of the body of water, e.g., by 5 to 10 parts per million (ppm), to consume accumulated organic material, destroy chloramines and/or control algae blooms. A shock treatment is administered by, for example, preparing a concentrated aqueous solution of calcium hypochlorite and adding this concentrated solution to the body of water, or distributing, e.g., broadcasting, granulated calcium hypochlorite directly over the surface of the body of water.
Use of boron derivatives, such as boric acid, sodium borates and potassium borates for inhibiting algal and fungal growth in recreational water systems, e.g., swimming pools, has been described. In addition, such compounds can serve as a pH buffer in the water. However, when boric acid is blended with solid calcium hypochlorite, e.g., granular calcium hypochlorite, the calcium hypochlorite assay, e.g., the FAC content of the calcium hypochlorite, in the resultant blend diminishes faster over time than an equivalent amount of the calcium hypochlorite used to prepare the blend that is substantially free of boric acid. Use of a low assay calcium hypochlorite can result in inadequate sanitization of water to which it is added. Therefore, it is desirable to provide a calcium hypochlorite-boric acid composition that is more stable, vis-à-vis, the loss of FAC assay, i.e., the composition has an improved shelf life.
Calcium hypochlorite is a material that can cause or enhance the combustion of organic materials by providing oxygen for combustion, e.g., it serves as an oxidizer. In accordance with US Department of Transportation (DOT) regulations; namely, Title 49, Code of Federal Regulations (CFR), part 173, section 127, paragraph (a), subparagraph (1), [49 CFR §173.127(a)(1)], calcium hypochlorite is categorized as a Division 5.1 oxidizer. More particularly, it is classified as a Packing Group II oxidizer material [49 CFR §173.127(b)(ii)]. The transport of a material categorized as a Division 5.1 oxidizer requires the use of special precautions, which can include the use of special containers.
Further, the National Fire Protection Association (NFPA) classifies calcium hypochlorite having greater than 50 percent FAC as a Class 3 oxidizer. NFPA Class 3 oxidizers may require separate free standing storage facilities and/or special sprinkler systems. Such special storage and handling requirements imposes increased costs on the use of calcium hypochlorite, particularly when the amount of calcium hypochlorite that is required to be stored on site is large.
Boric acid has been described as an exotherm control agent for peroxyacid compounds used in detergent compositions. However, as noted, when boric acid is blended with solid calcium hypochlorite, it tends to destabilize the calcium hypochlorite. Hence, blending boric acid with calcium hypochlorite would be counterproductive because it would lower the shelf life of the calcium hypochlorite, and perhaps even precipitate a runaway thermal decomposition, though mitigating the amount of heat released as a result of the thermal decomposition.
It would be advantageous to have solid halogen-containing compositions, e.g., calcium hypochlorite compositions that are not classified as a Packing Group I or Packing Group II Division 5.1 oxidizer, but are classified as a Packing Group III Division 5.1 oxidizer or as a non-Division 5.1 oxidizer. In the NFPA system, it would be advantageous to have solid halogen-containing compositions, such as calcium hypochlorite compositions, that are not classified as a Class 4 or Class 3 NFPA oxidizer, but are classified as a Class 1 or Class 2 NFPA oxidizer. Further, it would be advantageous that calcium hypochlorite compositions that contain boric acid do not lose FAC assay over time at a rate greater than an equivalent calcium hypochlorite composition that does not contain boric acid. It is also desirable that a solid calcium hypochlorite composition has an FAC assay that is at least sufficient to allow its use in the batch and/or continuous sanitization of water systems, e.g., a standing or recirculating water system such as a body of water, swimming pool, spa, hot tub, cooling tower, evaporative condenser, etc.