Chlorination

5 Key excerpts on "Chlorination"

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  Drinking Water Treatment, Calco-carbonic Equilibrium and Disinfection

  • Kader Gaid(Author)
  • 2023(Publication Date)
  • Wiley-ISTE

    (Publisher)

  To optimize disinfection, oxidant combinations are implemented, for example, a disinfection with ozone (germicidal effect) followed by additional Chlorination, before delivery into the network (residual effect). Ozone Chlorine Chlorine dioxide Chloramines UV Germicidal effect Residual effect ++++ 0 ++ ++ +++ ++ + +++ ++ 0 Table 21.8. Qualities of the main disinfectants 21.6. Chlorine disinfection Gaseous chlorine and chlorinated compounds are widely used for the disinfection of potable water. In solution, chlorine can exist in different states and react with certain organic or mineral molecules. Figure 21.5. Structural formula of chlorine The action of chlorine on microorganisms takes place on the surface and by slow diffusion. When microorganisms form clusters or are attached to suspended matter, the action of chlorine is much less effective because it does not completely diffuse inside the formed clusters. In addition, microorganisms can release polysaccharides, which create a kind of barrier which can reduce the effectiveness of Chlorination: Chlorination reagents: gaseous chlorine – bleach 122 Drinking Water Treatment 5 For disinfection purposes, chlorine can be used in three forms: – gaseous chlorine Cl 2 , stored under pressure in the liquid phase (cylinders, tanks); – sodium hypochlorite (or bleach), NaOCl (liquid); – calcium hypochlorite, Ca(ClO) 2 ·2H 2 O (solid). The first two forms, gaseous chlorine and bleach, are extremely common in water treatment. In all three cases, the disinfectant resulting from the reagent’s contact with the water to be treated is the same: hypochlorous acid HClO and hypochlorite (ClO – ). In general, the effectiveness of chlorine strongly depends on water pH due to the chemical equilibria between the different dissolved forms of chlorine (Table 21.9). For example, between a pH of 7.5 and 7.9, chlorine loses half of its effectiveness.

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  Drinking Water Quality and Contaminants Guidebook

  • Joseph Cotruvo(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  5 Disinfection and Chlorine Disinfectants

  Chlorination AND Chlorination DISINFECTION BY-PRODUCTS

  INTRODUCTION

  Chlorine in some form is the most widely used disinfection medium for drinking water, wastewater, and foods, and is also commonly used in swimming pools, cooling water systems, and surface sanitizing. It is applied as gaseous chlorine, sodium and calcium hypochlorites, monochloramine, and chlorinated isocyanurates or chlorine dioxide. Chlorine was introduced into drinking water treatment in the United States in the first decade of the 20th century and resulted in immediate reductions of waterborne diseases. Drinking water treatment and chlorine chemistry are also important in the food context because chlorinated drinking water or more highly chlorinated water is frequently used as a vehicle for food sanitation. So, we are commonly exposed to a variety of chlorine-related chemicals and the question is: Are there risks, and if so, what is the risk–benefit cost balance?

  DRINKING WATER USAGE

  The first continuous application of chlorine for drinking water in the United States was in Jersey City, New Jersey, in 1908 as calcium hypochlorite. The city’s typhoid fever death rate in 1895 was 80 per 100,000. They had switched to an alternate supply in 1906 and the rate was 21.4 per 100,000. After Chlorination was initiated the typhoid fever rates again declined dramatically. A few days prior to the Jersey City initiation, the Chicago stockyards began to chlorinate animal feed water to improve the animals’ health and weight gain. Within a decade, basically every large water supplier in the United States was chlorinating its drinking water, and by 1936, typhoid fever was essentially eradicated.

  CHLORINE PRODUCT MANUFACTURING

  Electrolysis of sodium chloride brine solution gives chlorine gas and sodium hydroxide, so it is inexpensive to produce. Hypochlorite is made by combining the chlorine with sodium hydroxide in solution. It is provided to water plants in about 15 percent solution and as laundry bleach in about 5 percent solution. Chloramines are produced on-site in the water treatment plant by reacting hypochlorite with ammonia or ammonium salts. The usual chlorine-to-ammonia weight ratio is around 5 so that the monochloramine is the dominant product. Chlorine dioxide is a gas that is made by reacting sodium chlorite with chlorine, or sodium chlorate with hydrochloric acid. It is unstable and explosive and it is made on-site for use without storage.

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  Water Supply

  • Alan C. Twort, Don D. Ratnayaka, Malcolm J. Brandt(Authors)
  • 2000(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  CHAPTER 11 Disinfection of Water

  11.1 Disinfectants Available

  The term ‘disinfection’ is used to mean the destruction of infective organisms in water to such low levels that no infection of disease results when the water is used for domestic purposes including drinking. The term ‘sterilisation’ is not strictly applicable because it implies the destruction of all organisms within a water and this may be neither achievable nor necessary. Nevertheless the word is often loosely used, as in ‘domestic water sterilizers’.

  On a plant scale the following disinfectants are in common use:

  • Chlorine (Cl2 );
  • Chloramines (NH2 Cl, NHCl2 )
  • Chlorine dioxide (ClO2 )
  • Ozone (O3 )
  • Ultra-violet (UV) radiation.

  For small plants or under special circumstances the following may be used: products releasing chlorine, (e.g. calcium hypochlorite (Ca(OCl)2 ), also called chloride of lime and sodium hypochlorite (NaOCl)).

  The organisms in water which it may be necessary to kill by disinfection include bacteria, bacterial spores, viruses, protozoa and protozoa cysts, worms and larvae. The efficacy of disinfection depends on numerous factors: the type of disinfectant used; the amount applied and the time for which it is applied; the type and numbers of organisms present; and the physical and chemical characteristics of the water.

  Chlorine and Chloramine Processes of Disinfection

  11.2 Action of Chlorine

  The precise action by which chlorine kills bacteria in water is uncertain but it is believed that the chlorine compounds formed when chlorine is added to water rupture bacterial membranes and inhibit vital enzymic activities resulting in bacterial death. Chlorine is also a strong oxidising agent that will break up organic matter in a water; but, in so doing, because it is a highly reactive chemical, it can form a wide range of chlorinated compounds with the organic matter present. Among these are the trihalomethanes (THM) and haloacetic acids (HAA) for which limits have been set for health reasons (Sections 6.25 , 11.7

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  Safe Drinking Water

  The Impact of Chemicals on a Limited Resource

  • Rip G. Rice(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 8Disinfectant Chemistry In Drinking Water–overview Of Impacts On Drinking Water Quality A.A. Stevens L. Moore R.C. Dressman, and D.R. Seeger U.S. Environmental Protection Agency Municipal Environmental Research Laboratory Drinking Water Research Division Cincinnati, Ohio 45268

  Chemicals commonly considered for use as disinfectants in municipal drinking water treatment are chlorine, chloramines, chlorine dioxide, and ozone. Considerations such as disinfection power, ease of application, and low cost in the past have led to the use of free chlorine (HOCl/OCl− ) as the primary disinfectant. Discovery of trihalomethanes, formed by the action of free chlorine upon natural organic materials such as aquatic humic materials, has led to a reexamination of this practice. In many cases a change to an alternative disinfection practice either has occurred or is being contemplated by utilities that otherwise have difficulty meeting the maximum contaminant level requirement for trihalomethanes. Chloramines, chlorine dioxide, or ozone when used alone do not usually cause significant formation of trihalomethanes. Each is an active oxidant, however, and has the potential of forming objectionable byproducts other than trihalomethanes (as may chlorine as well). Free chlorine, for example, forms quantities of “organic halogen” substantially in excess of those accounted for by the trihalomethanes. Chloramines and chlorine dioxide do also, although to a lesser extent than free chlorine. Specific reaction products of each in aqueous solution now are being identified. Thus, the beneficial use of each of these chemicals as a biocide in drinking water treatment may have its own less desirable side effects.

  Introduction

  When we were first asked to present a paper at this symposium on the subject of disinfectant chemistry in drinking water as an “overview” paper, we had in mind a somewhat traditional textbook approach describing in a brief way all the known basic chemistry. After reminding ourselves of the complexity of that, including the problem of distilling the huge volume of literature on that subject, we decided to take a different approach that we think is more appropriate for this group and better addresses the thrust of this symposium. That is, we plan to address the various perceived impacts of the application of disinfectant chemicals on drinking water quality in a comparative way and, to the extent it is understood, to relate these observations to the known chemistry of each disinfectant. The basic chemistry of the oxidants in water treatment, their uses as oxidants, as disinfectants, and of trihalomethane formation and control have been reviewed in a much more complete and detailed fashion elsewhere (1–5), and this material served as the source of much of the following discussion.

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  Photocatalysts

  Applications and Attributes

  • Sher Bahadar Khan, Kalsoom Akhtar, Sher Bahadar Khan, Kalsoom Akhtar(Authors)
  • 2019(Publication Date)
  • IntechOpen

    (Publisher)

  Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2. Methods of disinfections 2.1. Chlorine Gas Chlorine is a greenish-yellow gas. By providing high pressure, the gas becomes liquid. It is toxic. Chlorine gas is mostly used as a water disinfectant. Introducing chlorine to water plays a very effective role for removing almost all pathogenic microorganisms. It can be used both as a primary and a secondary disinfectant. The gas is not applicable to be used in household system as it is very dangerous. It is lethal at concentrations as low as 0.1% air by volume [1]. 2.1.1. Advantages • Chlorination is a cheaper source than UV or ozone disinfection methods used to treat water. • It is very effective against a wide range of pathogenic microorganisms. • Dosing rates are controlled easily as they are flexible. • The chlorine residuals left in the wastewater effluent can make the disinfection process lon -ger even after initial treatment. They can be further used to evaluate the effectiveness [ 2]. 2.1.2. Limitations Although chlorine gas is used in large-scale water distribution treatment plants and networks as a best method for treating water, still it have various limitations. These limitations might affect the applicability to a point of use (POU) treatment system. Objections against chlorina -tion are because of the esthetic, logistic, and health-related concerns. Regarding esthetic level, Chlorination might be rejected as it imparts bad tastes and odors to the water. The developed countries might teach their people about the good impacts of Chlorination; however, less-developed countries lack this ability.

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