Paper mills in the U.S. generate an enormous quantity of ClO2, 500 tons daily for bleaching pulp.Although more expensive than chlorine, it is the bleach material of choice because the basic properties of cellulose are not altered. The textile industry applies ClO2 similarly, where prevention of injury to the fibers is important. Both cellulosic and synthetic materials are processed in this way, including cottons, acetates, rayons, polyesters, acrylics and nylons. Cotton is not degraded because the oxidation reaction is highly selective toward lignin and hemicellulose components of the fiber. ClO2 does not adversely affect old paper prints or drawings, and will clean ancient documents without injury to fibers.
The first use of chlorine (Cl2) as a water treatment process in the U.S. occurred in Jersey City in 1908, and of chlorine dioxide, at Niagara Falls in 1944.ClO now purifies water in over 500 water treatment facilities in the U.S. and many more in Europe. Only chlorine dioxide among the common water treatment disinfectants (ozone, chlorine, chloramine, and chlorine dioxide), produces no signs of malignancy in test animals. ClO is often applied for water treatment other than disinfection, for example, remedying difficult smell and taste problems. Phenols, in particular, are quickly oxidized, and without odorous chlorophenols often produced by chlorine. ClO2 is considered the best additive for oxidizing iron and manganese impurities in drinking water, and for eliminating taste and odor due to algae.It also removes cyanides sulfides, aldehydes and mercaptans. ClO2 as used in water disinfection is more sporicidal than Cl2 , a more powerful inactivator of viruses, and inactivator of cysts. In storm water overflow, ClO has proved active toward all viruses examined.
Another application of ClO2 is in the bleaching of fats and flour.
Extensive experience with chlorine dioxide bleaching of tallow (the fat extracted from meat scraps and dead animals) has shown that this is a safe chemical bleaching process. The chlorine dioxide selectively converts color bodies to lighter colored ones without substantial attack on natural antioxidants in the oil which protect it against aging and rancidity. Tallows bleached with Chlorine dioxide meets the “Refine and Bleach Test”, is color stable, and is now in use for the manufacture of the highest-grade toilet soaps.
Many nutrition and toxicology studies have been performed assessing chlorine dioxide’s effect on flour. Treatment of flour with 200 ppm, fed to rats, had no effect after several generations.
Flour treated with up to 500 ppm (5 times the concentration in DioxiCure Gel) fed to puppies had no untoward effect. Thirteen human subjects fed experimentally for six weeks with flour products that were treated with doses up to 400 ppm had no detectable toxic symptoms. Flour bleached with normal dosage is not reduced appreciably in nutritive value.Essential fatty acids are generally not effected, but tocopherol and cystine are oxidized. Reactivities of 21 amino acids with ClO2 were evaluated using an iodmetric assay, only 6 were found to be reactive at pH6. They were cysteine, histidine, hydroxyproline, proline, tryptophan and tyrosine.
Several other applications within the food industry have been described. The first reported use of ClO2 in the canning industry was by Green Giant at LeSueur, Mn. more than 30 years ago. The objective was to conserve water while at the same time control bacteria. When ClO Rather than chlorine is added to process waters recirculated to clean potatoes, starch by-product, previously extracted for gluing cartons, is upgraded to food grade level and a higher market value. Also, the fresh water need is reduced 25%. In this particular process 10 ppm ClO2 is added to the wash water in order to maintain a 1 ppm residual. Chlorine dioxide is excellent as a commercial disinfectant in turkey egg sanitation, and its use does not modify the hatching properties of the fertile eggs. The shelf life of tomatoes can be improved by treatment with ClO2.
ClO2 also finds application in bleaching cherries and as a teat dip for cows to prevent mastitis. The FDA has recently permitted the use of ClO2 for disinfecting chickens, beef and fruits and vegetables.
Masschelein, in his book Chlorine Dioxide, cites the following:
Chlorine dioxide destroys the microorganisms in fish, fruits and vegetables; and the treatment can be carried out without altering the nutritive and organoleptic qualities of the foodstuff. It will take place either by 30-minute immersion in an aqueous solution of 50 to 1,000 mg/1 (50 to 1000ppm) of ClO2 or by exposure to air containing 2,000 to 3,000 ppm of ClO2. This is a very favorable treatment for the storage of frozen foods. Natural foods such as pepper may be sterilized by a treatment with air containing 1,000 to 20,000 ppm of ClO2. The preservation of melted cheese is facilitated by the addition of 100 to 300 mg/1 of ClO2 to the milk used for its manufacture, and 100 to 400 mg/1 to its washing water. The bleaching of oils and greases, particularly those used for alimentary needs, is carried out by a maximum injection of 20,000 mg/1 of ClO2. The medicinal odor of cleaning shrimps is eliminated by adding 40 mg/1 to the washing water. A dose of less than 100 mg/1 of ClO2 does not seem to hinder the taste or nutritive value.
The remaining or residual products on fruits and vegetables after treatment with ClO2 are apparently chloride and a trace amount of chlorite. A recent patent by Frontier Pharmaceutical involves the lowering of the chlorite residual, and describes a method for the release of ClO2 at higher, more physiological pH.
Some industrial applications of ClO2 other than bleaching or disinfecting include: the treatment of leather, where ClO2 oxidizes disulfide bridges of keratin; stabilization of vinyl and latex enamels; additive in air pollution control for complexing impurities such as mercaptans and aldehydes; controlling odors of fishmeal and rendering plant water effluents; an oxidant in the preparation of vaccines , and neutralizing toxins; and a copper etchant in the manufacture of electronic component parts.