Hypochlorites sanitization

The ideal recommended cyanuric acid concentration is 30—50 ppm (Table 2). Although this range can be readily maintained when using hypochlorite sanitizers, it cannot be maintained when using chloroisocyanurates since they increase the cyanuric acid concentration. The NSPI recommends a maximum of 150 ppm cyanuric acid. Many health departments limit cyanuric acid to 100 ppm. No significant increase in stabilization occurs beyond 50—100 ppm, and since high levels of cyanuric acid slow down the rate of disinfection, the pool water should be partially drained and replaced with fresh water to reduce the cyanuric acid to below recommended maximum levels. Cyanuric acid is determined turbidimetricaHy after precipitation as melamine cyanurate. 

For hypochlorite sanitizers 100—120 ppm for acidic sanitizers, chlorine, Dichlor, Trichlor, and bromine compounds. 

Lithium Hypochlorite. Lithium hypochlorite [13840-33-0], LiOCl, is obtained from reaction of chlorine and an aqueous solution of lithium hydroxide. The soHd is usually obtained as a dry stable product containing other alkaH haHdes and sulfates (64). A product containing 35% available chlorine is used for sanitizing appHcations in swimming pools and in food preparation areas where its rapid and complete dissolution is important. The salt can also be obtained in higher purity by reaction of lithium hydroxide and hypochlorous acid (65). 

NaOH for stabiUty which has only a small effect on pool pH. It is a commonly used sanitizer for swimming pools. In pool water, it produces hypochlorite ion and hypochlorous acid ... 

Calcium Hypochlorite. This chemical, marketed since 1928, is one of the most widely used swimming-pool water sanitizers. Calcium hypochlorite, a crystalline sofld, is a convenient source of available chlorine and is sold in granular or tablet form for use in home, semiprivate, and commercial pools. When dissolved in water, Ca(OCl)2 forms hypochlorous acid and hypochlorite ion similar to NaOCl. It contains small amounts of stabilizing Ca(OH)2, which has a very small effect on pool pH (7). Calcium hypochlorite has superior storage stabiUty and much higher available CI2 concentration than Hquid bleach, which reduces storage requirements and purchasing frequency. 

Sodium bicarbonate is generally added to increase alkalinity and muriatic acid (HCl) or sodium bisulfate (NaHSO ) to reduce it. In general, with acidic sanitizers such as chlorine gas or trichloroisocyanuric acid, ideal total alkalinity should be in the 100—120 ppm range, whereas, with alkaline products such as calcium, lithium, or sodium hypochlorite, a lower ideal total alkalinity of 80—100 ppm is recommended (14). Alkalinity is deterrnined by titration with standard sulfuric acid using a mixed bromcresol green—methyl red indicator after dechlorination of the sample with thiosulfate. Dechlorination with thiosulfate causes higher readings due to formation of hydroxyl ion (32) ... 

Sanitizers. Spa and hot-tub sanitation is dominated by chlorine- and bromine-based disinfectants. Public spas and tubs usually employ automatic feeders, eg, CI2 gas feeders, to maintain a disinfectant residual. Private or residential spas and tubs can use automatic chemical feeding or generating devices, or they can be sanitized manually with granular or liquid products. The most widely used products for private spa and tub sanitation are sodium dichloroisocyanurate and bromochlorodimethylhydantoin. Granular products are normally added before and after use, whereas solids, eg, stick-bromine, are placed in skimmers or feeders. Bromine generating systems can also be used and are based on oxidation of bromide ions (added to the water as sodium bromide) by peroxymonosulfate, chloroisocyanurates, hypochlorites, or ozone to generate the disinfectant HOBr. 

Historically, bleaching powder and tropical bleach were significant sources of available chlorine but very Httle are used today. This is because of the greater availabiUty of sodium hypochlorite solutions and the development of calcium hypochlorite. They are stiU used to sanitize fields, drainage ditches, and reservoirs where its insoluble portion is not important. And, they are important sources of available chlorine within some less developed tropical countries. 

Some hypochlorites, either as solutions or soflds, are much more stable than hypochlorous acid, and because of thek high oxidation potential and ready hydrolysis to the parent acid, find wide use in bleaching and sanitizing appHcations. One of the novel uses of hypochlorites was for disinfection of ApoUo Eleven on its return from the moon (136). 

Sodium Hypochlorite (Liquid Bleach). Commercial strength Hquid bleach used by industries, laundries, and in swimming pool sanitation, contains 12—15% av CI2 and is sold in 3.8- and 7.6-L polyethylene bottles and 23—57-L carboys, 205-L dmms, and tank tmcks of about 3-kI capacity and greater. Household bleach contains about 5% av CI2 and is sold in 1—5.7-L polyethylene containers. Shipping is limited within a short radius of the plant... 

Economic Aspects. Lithium hypochlorite is produced by Lithium Corporation of America (a subsidiary of FMC) at its plant in Bessemer, North Carolina which has a capacity of about 4000 t/yr. Its total demand is low owing to its relatively high price of about 1.27/lb in tmckload quantities. Estimated U.S. consumption in 1987 was 2000—2500 t, 80—90% being used in swimming pool sanitation. 

Applications. Lithium hypochlorite, first introduced in 1964, has limited use in swimming pool and spa sanitation and dry laundry bleaches. 

Calcium Hypochlorite. High assay calcium hypochlorite [7778-54-3] was first commercialized in the United States in 1928 by Mathieson Alkali Works, Inc. (now Olin Corp.) under the trade name HTH. It is now produced by two additional manufacturers in North America (Table 5). Historically, it usually contained about 1% water and 70—74% av CI2, so-called anhydrous product, but in 1970, a hydrated product was introduced (234). It is similar in composition to anhydrous Ca(OCl)2 except for its higher water content of about 6—12% and a slightly lower available chlorine content. This product has improved resistance to accidental initiation of self-sustained decomposition by a Ht match, a Ht cigarette, or a small amount of organic contamination. U.S. production in the 1990s consists primarily of partially hydrated Ca(OCl)2, which is sold as a 65% av CI2 product mainly for swimming pool use. Calcium hypochlorite is also sold as a 50% av CI2 product as a sanitizer used by dairy and food industries and in the home, and as a 32% product for mildew control. 

Calcium Hypochlorite, also known as High Test Hypochlorite (HTH) is supplied in erystal form it is nearly 70% available chlorine. One produet, the Sanitizer (formally the Sierra Water Purifier) uses these erystals to superehlorinate the water to insure pathogens were killed off, then hydrogen peroxide is added to drive off... 

Chlorine, or more commonly a substance containing hypochlorite ion, is added to pools as a disinfectant. However, sunlight rapidly destroys hypochlorite, drastically reducing the effectiveness of the sanitizer. Hence, the effectiveness of the disinfectant is maximized when added in the evening hours. 

Lithium hydroxide, 15 134, 140-141 Lithium hypochlorite, 4 52 15 141 pool sanitizer, 26 175 Lithium iodide, 3 417 15 140 Lithium-iodine cells, 3 463-464 characteristics, 3 462t speciality for military and medical use, 3 430t... 

Postharvest washing of vegetables remains the key intervention to remove field acquired contamination. There have been numerous papers and reviews on the relative performance of different sanitizers including hypochlorite, chlorine dioxide, and peroxyacetic acid (Allwood et al, 2004 Gonzalez et al., 2004 Ibarra-Sanchez et al, 2004 Koseki and Isobe, 2006 Rodgers et al., 2004 Romanova et al, 2002). 

Sodium hypochlorite is the primary hypochlorite used as a bleach and disinfectant, accounting for 83% of world hypochlorite use, with calcium hypochlorite accounting for the remaining 17%. Approximately 1 million tons of sodium hypochlorite was used globally in 2005, with about half this amount used in households for laundry bleaching and disinfection. The other half was used primarily for wastewater and drinking water treatment other uses include pool sanitation, bleaching of pulp, paper, and textiles, and as an industrial chemical. 

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