Hypochlorites water disinfection

Hypochlorous Acid. Hypochlorous acid [7790-92-3] solutions are made for immediate use as chemical intermediates from chlorine monoxide or in bleaching and water disinfection by adjusting the pH of hypochlorite solutions. Salt-free hypochlorous acid solutions have been economically made... 

Lopez A, Mascolo G, Tiravanti G, Passino R (1997) Degradation of herbicides (ametryn and isoproturon) during water disinfection by means of two oxidants (hypochlorite and chlorine dioxide). Water Sci Technol 35 129-136... 

Kraft, A., Stadelmann, M., Blaschke, M., Kreysig, D., Sandt, B. and Schroeder, F. (1999a) Electrochemical water disinfection, part I Hypochlorite production from very dilute chloride solutions. J. Appl. Electrochem. 29, 861-868. 

Kraft A, Blaschke M, Kreysig D, Sandt B, Schroder F, Rennau J. (1999b). Electrochemical water disinfection. Part II Hypochlorite production from potable water, chlorine consumption and the problem of calcareous deposits. Journal of Applied Electrochemistry 29 895-902. 

Acetyl chloride water disinfection Sodium hypochlorite water evaporation retardant, cements Hydroxyethylcellulose water evaporation retardant, mortars Hydroxyethylcellulose water glass mfg. 

Hypochlorite can be produced by the reaction of chlorine gas with sodium hydroxide solution. On-site generation of hypochlorite avoids storage and transport difficulties associated with chlorine gas, and is convenient for many applications, including sewage treatment, sterilisation of water, disinfection, biological growth prevention and enhanced oxidation of, for example, cyanide wastes. The electrochemical generation of hypochlorite has been the subject of several reviews (see [84]). 

Electrolytic cells are also used in a variety of devices - and appliances " to produce dilute solutions of electrolyzed water for cleaning and sanitization. Miniature, battery-powered cells are used to generate hypochlorite in handheld sprayers and small portable water disinfection devices. " " The brine may be saturated or have 1-5 g L of salt. An acidic solution of chlorine, hypochlorous acid, and possibly chlorine dioxide is obtained from the anode of a divided cell. It typically has 10-100 mg L of available chlorine and pH values of 2-4. Its stability is poor, and the volatile oxidants are rapidly lost from open solutions. A neutral solution of hypochlorous acid and sodium hypochlorite is dispensed from undivided cells or by combining effluents from the anode and cathode. It typically has 80-100 mg L of available chlorine and pH 5-8. Devices to make 500-1000 mg L" of available chlorine are also available. Neutral solutions made using larger versions of these devices are bottled and sold in some regions. 

Calcium hypochlorite, solid Disinfectants Water treating chemicals Chlorine bleaches... 

In the water treatment sector, NaOH is used for the regeneration of ion exchangers for water purification, pH-adjustment, waste water treatment, drinking and swimming pool water disinfection by treatment with hypochlorite solution. 

Uses of diluted hypochlorite solutions are in the pulp and paper and the textile industry for bleaching, water disinfection, biofouling control in desalinating projects and power generation sites, disinfection of seawater for secondary oil recovery, food production. 

As shown by reactions (9)-(ll), the end products of hypochlorite decomposition in the original container are chloride and chlorate ions in addition to oxygen gas. Disregarding the relatively small amount of chloride produced by reaction (11), the final solution would contain NaCl and NaClOa in a 2 1 molar ratio. The overall rates and amounts of chlorate formation at pH s above about 11 can be estimated for any given initial hypochlorite solution by means of the equations in Ref. 5. Data on actual amounts of chlorate found in various hypochlorite solutions used in water disinfection have been assembled and analyzed [14,15]. 

Trisodium phosphate is strongly alkaline many of its appHcations depend on this property. For example, many heavy-duty cleaning compositions contain trisodium phosphate as a primary alkalinity source. The crystalline dodecahydrate itself is marketed as a cleaning compound and paint remover. Traditionally, trisodium phosphate has been used in water softening to remove polyvalent metal ions by precipitation as insoluble phosphates. Because the hypochlorite complex of trisodium phosphate provides solutions that are strongly alkaline and contain active chlorine, it is used in disinfectant cleaners, scouring powders, and automatic dishwashing formulations. 

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. 

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. 

The largest use of calcium hypochlorite is for water treatment. It is also used for I I and household disinfectants, cleaners, and mildewcides. Most of the household uses have been limited to in-tank toilet bowl cleaners. In areas where chlorine cannot be shipped or is otherwise unavailable, calcium hypochlorite is used to bleach textiles in commercial laundries and textile mills. It is usually first converted to sodium hypochlorite by mixing it with an aqueous solution of sodium carbonate and removing the precipitated calcium carbonate. Or, it can be dissolved in the presence of sufficient sodium tripolyphosphate to prevent the precipitation of calcium salts. However, calcium hypochlorite is not usually used to bleach laundry and textiles because of problems with insoluble inorganic calcium salts and precipitation of soaps and anionic detergents as their calcium salts. 

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