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Sodium Chlorite Treatment of Drinking Water with Chlorine Dioxide

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Sodium Chlorite Treatment of Drinking Water with Chlorine Dioxide ® Basic Chemicals Sodium Chlorite Treatment of Drinking Water with Chlorine Dioxide 3 Introduction documented in the laboratory, in pilot studies and in Chlorine dioxide is a powerful oxidizing agent, full-scale studies using potable and waste water. generated from sodium chlorite. Its selective reactivity Unlike chlorine, chlorine dioxide does not hydrolyze in makes chlorine dioxide useful in many water treating water. Therefore, its germicidal activity is relatively applications for which chlorine and other oxidizing constant over a broad pH range (See Figures 1, 2, and agents are unsuitable. 3 on Page 6 and 7). Chlorine dioxide was first used in municipal drinking At pH 6.5, doses of 0.25 mg/L of chlorine dioxide and water treatment in 1944 to control taste and odor at chlorine produce comparable one-minute kill rates for the Niagara Falls water treatment plant. Today, there the bacterium Escherichia coli. At pH 8.5, chlorine is increased interest in chlorine dioxide as an oxidant dioxide maintains that same kill rate, but chlorine and disinfectant for drinking water. Recently, this requires five times as long. Thus, chlorine dioxide interest has been stimulated by the publication of the should be considered as a primary disinfectant for high final Disinfectants and Disinfection Byproducts Rule1 pH, lime-softened waters. (DBPR) as part of the EPA's National Primary Drinking Water Regulations. Chlorine dioxide has also been shown to be effective in killing other infectious bacteria such as This rule sets a maximum contaminant level (MCL) of Staphylococcus aureus and Salmonella. Chlorine 0.08 mg/L for total trihalomethanes (TTHM). The EPA dioxide is as effective as chlorine in destroying has identified chlorine dioxide as an alternative or coliform populations in waste water effluents, and is supplemental oxidant-disinfectant that is one of the superior to chlorine in the treatment of viruses most suitable for TTHM treatment and control2. commonly found in secondary waste water effluents (Figure 4). When Poliovirus I and a native coliphage In contrast with chlorine, the reactions of chlorine were subjected to these two disinfectants, a 2 mg/L dioxide with humic substances (the precursors of dose of chlorine dioxide produced a much lower 4 trihalomethanes) do not result in the formation of survival rate than did a 10 mg/L dose of chlorine . THMs. For this reason, chlorine dioxide treatment has become a preferred method where it is necessary to control TTHMs, along with taste and odors. Chlorine Dioxide as a Water Disinfectant Chlorine dioxide is an extremely effective disinfectant and bactericide, equal or superior to chlorine on a mass dosage basis. Its efficacy has been well 600-202 Sodium Chlorite 08/2018 Important: The information presented herein, while not guaranteed, was prepared by technical personnel and is true and accurate to the best of our knowledge. NO WARRANTY OF MERCHANTABILITY OR OF FITNESS FOR A PARTICULAR PURPOSE, OR WARRANTY OR GUARANTY OF ANY OTHER KIND, EXPRESS OR IMPLIED, IS MADE REGARDING PERFORMANCE, SAFETY, SUITABILITY, STABILITY OR OTHERWISE. This information is not intended to be all-inclusive as to the manner and conditions of use, handling, storage, disposal and other factors that may involve other or additional legal, environmental, safety 14555 Dallas Parkway, Suite 400 or performance considerations, and Occidental Chemical Corporation assumes no liability Dallas, TX 75254 whatsoever for the use of or reliance upon this information. While our technical personnel will be happy to respond to questions, safe handling and use of the product remains the 800-752-5151 responsibility of the customer. No suggestions for use are intended as, and nothing herein shall be construed as, a recommendation to infringe any existing patents or to violate any Federal, State, local or foreign laws. ® Basic Chemicals viruses and Legionella. The published CT values (40 CFR 141.74) required for various disinfectants to achieve these goals show that chlorine dioxide is more effective than chlorine or monochloramine. Over the pH 6-9 range, chlorine dioxide is at least twice as effective as free chlorine is at pH 6. At pH 7-9, free chlorine becomes progressively less effective than chlorine dioxide. Chlorine dioxide is also substantially more effective than monochloramine. Chlorine Dioxide For Control Of THMs In 1974, researchers first observed the formation of trihalomethanes (THMs) during chlorination of natural waters. These THMs (chloroform, bromodichloro- methane, dibromochloromethane, and bromoform) are produced when free chlorine or bromine reacts with natural organic matter in the water. The subsequent identification of THMs in chlorinated water supplies led to concerns over their potential health effects. These concerns include potential reproductive effects and the classification of chloroform, bromodichloromethane and certain other disinfection byproducts (DBPs) as carcinogens. In 1979, the EPA established a THM Maximum Contaminant Level (MCL) of 0.10 mg/L, causing water When applied for disinfection (as opposed to utilities to begin searching for alternatives to chlorine oxidation), a disinfectant must provide specified levels for oxidation and disinfection of water. The recent of microorganism kills or inactivations as measured by DBPR1 not only lowered the MCL for total reductions of coliforms, heterotrophic plate count trihalomethanes (TTHMs) to 0.08 mg/l, but also organisms and Legionella bacteria. Under current extended the MCL to all size systems. In addition, a regulations5, the disinfection treatment must be new MCL of 0.06 mg/L was established for haloacetic sufficient to ensure at least a 99.9 percent (3-log) acids (HAA5). As a result, there is an increased removal and/or inactivation of Giardia lamblia cysts emphasis on the modification of water treatment and 99.99 percent (4-log) removal and/or inactivation methods to prevent or reduce the formation of THMs of enteric viruses. Disinfection is expressed as a CT and other DBPs to ensure compliance with the new value (i.e., a function of Concentration x Contact EPA rule. For this purpose, chlorine dioxide is an Time). At the CT values necessary for chlorine dioxide excellent choice as either an alternative or to inactivate 99.9 percent of Giardia lamblia cysts, the supplemental oxidant-disinfectant. simultaneous inactivation of 99.99 percent of enteric viruses is also assured. The key to understanding why chlorine dioxide is so effective can be found in the differences in the These regulations also establish treatment technique reactions of chlorine dioxide and chlorine with THM requirements in lieu of MCLs for Giardia lamblia, precursors, such as humic and fulvic acids. Chlorine 600-202 Sodium Chlorite 08/2018 Important: The information presented herein, while not guaranteed, was prepared by technical personnel and is true and accurate to the best of our knowledge. NO WARRANTY OF MERCHANTABILITY OR OF FITNESS FOR A PARTICULAR PURPOSE, OR WARRANTY OR GUARANTY OF ANY OTHER KIND, EXPRESS OR IMPLIED, IS MADE REGARDING PERFORMANCE, SAFETY, SUITABILITY, STABILITY OR OTHERWISE. This information is not intended to be all-inclusive as to the manner and conditions of use, handling, storage, disposal and other factors that may involve other or additional legal, environmental, safety 14555 Dallas Parkway, Suite 400 or performance considerations, and Occidental Chemical Corporation assumes no liability Dallas, TX 75254 whatsoever for the use of or reliance upon this information. While our technical personnel will be happy to respond to questions, safe handling and use of the product remains the 800-752-5151 responsibility of the customer. No suggestions for use are intended as, and nothing herein shall be construed as, a recommendation to infringe any existing patents or to violate any Federal, State, local or foreign laws. ® Basic Chemicals dioxide reacts primarily by oxidation; however, chlorine These findings can be the basis of water treatment reacts by both oxidation and electrophilic substitution practices designed to minimize THM formation. Most to yield volatile and nonvolatile chlorinated organic often, chlorine dioxide for THM control is a substances (THMs). replacement for prechlorination. The addition of Figure 5 chlorine dioxide to the raw water supply would be for primary disinfection and/or oxidation. Then, free or Chloroform production in water containing 5 mg humic acid combined chlorine or chlorine dioxide is added after dosed with chlorine dioxide or free chlorine filtration to provide a disinfectant residual in the distribution system. 120 ug/L) 100 With such treatment, THM precursors are oxidized by the chlorine dioxide. The next treatment steps 80 (coagulation, settling and filtration) remove the oxidized precursors before final chlorination. 60 Preoxidation dosages with chlorine dioxide are 40 Chlorine Dioxide Free Chlorine typically 30 to 50 percent of the required prechlorination dosages. Postchlorination dosage, 20 however, might be slightly higher than the dosage Chloroform Concentration ( 0 without using chlorine dioxide. This modification of 0 5 10 15 20 25 30 35 40 45 50 standard chlorination practices can result in a 50 to 70 Reaction time (hours) percent (50% - 70%) decrease in TTHMs. Many treatment methods have been developed to Chlorine dioxide is not only economical, but is also remove THMs once they have been formed by effective in preoxidation and disinfection. Typically, chlorine treatment. However, chlorine dioxide
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