Disinfection of Drinking Water Rich in Bromide with Chlorine and Chlorine Dioxide, While Minimizing the Formation of Undesirable By-Products
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Abstract:
Although chlorine dioxide does not form trihalomethanes (THM) and produces very few non-volatile haloorganic materials in drinking water, intensive investigations bearing on the formation of chlorite by ClO2 disinfection reveal that the rate of chlorite formation reflects the rate of ClO2 consumption and as long as the amount of ClO2 applied is behind its demand, about 60% of the chlorine dioxide consumed is converted into chlorite. Mixtures of Cl2 and ClO2, which may successfully reduce the formation of haloorganic compounds, as well as of chlorite in the absence of bromide, fail to do this where water rich in bromide is concerned. As a result of bromide oxidation by chlorine, bromine is formed, which in turn reacts more intensively with organics than does chlorine and thus favours the formation of THM and other halogenated organic materials. This problem can, however, be circumvented if ClO2 is allowed to react in water with the organic precursors before chlorine is introduced. A pre-treatment with 1 ppm of ClO2 two hours before the application of 2 ppm Cl2, was found to reduce the formation of THM by 60% relative to its formation by chlorine alone, and the chlorite is reduced in this case by up to 90% relative to its formation by chlorine dioxide alone. This is of particular importance since it can solve some of the major problems bearing on the impact of disinfection upon the formation of undesirable by-products.Keywords:
Sodium chlorite
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酸化塩素(IV)水溶液による酸化漂白についてはその漂白機構がよく知られていない。本報では酸化塩素(IV)水溶液の酸化電位を測定することによってこれを研究しようと試みた。実測の結果酸化塩素(IV)水溶液の酸化電位は,酸化塩素(IV)の溶存濃度には無関係であることが明らかとなった。したがってこの電位はつぎの平衡に基づくと考えるのが妥当であろうまた実測値より酸化塩素(IV)の加水分解における平衡定数が求められた。酸化塩素(IV)水溶液の酸化作用の機構については,最初は酸化塩素(IV)がイオン化するときの酸化力と,つぎに2次的に生成するClO2○-による酸化力との二つに分けて考えられる。
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Abstract The formation of the by-product chlorite after using chlorine dioxide for the disinfection of drinking water depends on the quantity of the organic matter dissolved in the water. A further decisive factor for the chlorite formation is the level of residual free chlorine dioxide. The chlorine dioxide demand decreases by application of activated carbon filtration, especially after the use of a combination of ozone and activated carbon treatment of the water. Nevertheless, higher chlorine dioxide residuals are a source of chlorite and chlorate formation. The concept of the “Minimum Chlorine Dioxide Dosage (MCDD)” is developed in order to give a clue to the water companies for an optimized chlorine dioxide dose without compromising the disinfection efficiency. By application of the MCDD, the residual level of chlorine dioxide is focused to 0.05 mg/L after 0.5 h contact time. In the range of the MCDD the ratio of the chlorite formation and the chlorine dioxide demand is nearly independent of the level of DOC. Key Words: OzoneDisinfectionChlorine DioxideChloriteChlorateMinimum Chlorine Dioxide Dosage (MCDD)Trihalomethane FormationGermany Drinking Water Treatment
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cis-[Ru(2,9-Me(2)phen)(2)(OH(2))(2)](2+) reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(II) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite.
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This article discusses the magnitude of chlorite ion (ClO2) and chlorate ion (ClO3) formation and analytical methods for measuring chlorine dioxide byproducts; specifically, amperometric titration versus ion chromatography. The Fort Collins, Colorado, water treatment facility produces chlorine dioxide by using a generator that causes chlorine gas to react with a 25% sodium chlorite solution under vacuum conditions. The experiences of this water treatment facility are discussed as a case study.
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This paper aims to study the generating regularity of the inorganic by-product chlorite in the algae preoxidation with chlorine dioxide in drinking water processing.For this purpose,we have made an investigation over the generating regularity of chlorite under the conditions of different dosages of chlorine dioxide,contact time and pH.We have also studied the other influencing factors related to water quality,such as algal initial concentration,organic substances and ammonia nitrogen concentration on the generation of the by-product chlorite.The testing and investigation results show that the by-product chlorite increases with the increase of the dosage of chlorine dioxide.In addition,it is found that time is the key factor to influence the generation of chlorite.Actually,large amounts of chlorite would be resulted in 30 minutes.Two hours later,we may find that there would be generated chlorite which is 10 to 30 percent of chlorine dioxide,with an initial pH value beginning to generate the chlorite.The longer the contact time,the lower the initial pH would be.30 minutes later after a 10 minute reaction,the initial pH value would increase to 6.However,70 minutes later,the initial pH value would turn to be 3.9.Furthermore,the chlorite would gradually increase in the acidity condition while the pH value would change from low to high.Nevertheless,when the pH changes from neutral to alkalinity,little increase would be found of the chlorite in final analysis.But,when the algal chlorophyll-a concentration remains below 14.93 μg/L,no variation of the amount of by-product chlorite could be found with the initial algal concentration.However,when the algal chlorophyll-a concentration is greater than 14.93 μg/L,the chlorite tends to increase with the increase of the algal initial concentration.Though the organic matter is likely to promote the formation of chlorite,the chlorite wouldn't be found increasing with the increase of the concentration of the organic matter,which demonstrates a decreasing trend with the increase of the ammonia nitrogen concentration.And the residual chlorine dioxide is found decreasing with the time prolonging in the process of the formation of chlorite.Based on the regression analysis of the experimental data,the relation between the residual chlorine dioxide and the time to be elapsed seems to be a function of the power series in the generation of the by-product chlorite.
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Abstract The role of chlorine (III) compounds, i.e. chlorous acid (HClO 2 ) and chlorite (ClO 2 - ), in chlorine dioxide bleaching were investigated by treating different pulps with Cl(III). It was discovered that in addition to its fully inorganic reactions, chlorous acid is consumed by organic structures present in the pulp. These structures were assumed to be aldehydes. The aldehydes might exist already in unbleached pulps, but chlorine dioxide bleaching was also found to generate new aldehyde groups. The reactive groups were concluded to originate both from carbohydrates and lignin.
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Abstract A novel method is developed using formaldehyde as catalyst for the oxidation of sodium chlorite to chlorine dioxide.
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Abstract : The reaction of the formation of chlorine dioxide from hypochlorous acid and chlorite in aqueous solutions, which was studied in the present research is gHOCl + hClO2(-) yields pCl0w + qCl03(-) + rCl(-). Since chlorine dioxide, chlorite and hypochlorous acid have different absorption peaks in the ultra-violet range, the spectrophotometer was used as the method of analysis. Kinetic analysis of the concentration values of hypochlorous acid, chlorine dioxide and chlorite changing with time during the course of the reaction reveals that the rate of the overall reaction is first order with respect to the two reactants under the range of experimental conditions used. The yield of chlorine dioxide from chlorite varied from 35 to 65% within the experimental conditions described. It was observed that the majority of the chlorite consumed was oxidized to chlorine dioxide or chlorate whereas the hypochlorous acid consumed was reduced to chloride. A mechanism is suggested in which Cl2O2 is the activated intermediate complex. This mechanism suggests that the formation of the intermediate is the slow rate determining step.
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