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1.4: Chloramination

  • Page ID
    5726
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    Learning Objectives

    • Describe chloramination
    • Outline the uses of chloramination
    • Explain the formation of chloramines

    Chloramines are disinfectants used to treat drinking water and they:

    • Are most commonly formed when ammonia is added to chlorine to treat drinking water
    • Provide longer-lasting disinfection as the water moves through pipes to customers

    Chloramines have been used by water utilities since the 1930s. One in five Americans use drinking water treated with chloramines for disinfection. Water that contains chloramines and meets EPA regulatory standards is safe to use for:

    • Drinking
    • Cooking
    • Bathing
    • Other household uses

    Many public water systems (PWSs) in the United States use chlorine as their secondary disinfectant. However, some PWSs have changed their secondary disinfectant to chloramines in order to meet disinfection byproduct requirements.

    Chloramination is the treatment of drinking water with a chloramine disinfectant. Chlorine and small amounts of ammonia are added to water one at a time. These chemicals react to form chloramine (combined chlorine), which is a long-lasting disinfectant. Chloramine disinfection is sometimes used in large distribution systems.

    In the United States, the maintenance of a disinfection residual that remains measurable in the water distribution system is required by the EPA.

    EPA regulations provide two choices for disinfectant residual. They are chlorine or chloramine. Many major water agencies are changing to chloramine to better meet current and anticipated federal drinking water regulations and to protect public health.

    Chloramine is toxic to fish and amphibians. Chloramine, like chlorine, comes in direct contact with their bloodstream through their gills, and it must be removed from water added to aquariums and fish ponds. It must also be removed from the water prior to use in dialysis machines, since the water comes into direct contact with a patient’s bloodstream during treatment.

    Chloramine is generally considered a problem in brewing beer because it can react with and change some of the natural plant flavors that make up beer. It may slow or alter the yeast activity. Because chloramine dissipates much more slowly than chlorine from water, beer-makers prefer carbon filtration to neutralize chloramines in the water.

    Much of the recent discussion concerning chloramine has focused on N-nitrosodimethylamine (NDMA), and it is critical to distinguish between chloramine and NDMA. NDMA can be a byproduct of chloramination or chlorination; however, drinking water is not a major source of exposure to NDMA. The biggest sources of human exposure to NDMA is tobacco smoke, chewing tobacco, bacon and other cured meats, beer, fish, cheese, toiletries, shampoos, cleansers, interior air of cars, and household pesticides. In addition, NDMA can form in the stomach during digestion of foods or drugs that contain alkylamines, which are naturally occurring compounds.

    At very high levels, NDMA may cause serious human health problems, such as liver disease. Such effects are seen at concentrations ranging from 5 to 50 parts per million in water; for comparison, a study conducted by the California Department of Health Services in 1999 and 2000 found the highest level of NDMA in drinking water that had been treated with chloramine was 0.00006 parts per million. In that study, most of the concentrations of NDMA were far lower than that, and many water samples in the California Department of Health Services study did not have any detectable concentrations of NDMA.

    Chloramination

    Chloramination is used as an alternative disinfection process in place of free chlorine. An operator’s decision to use chloramine in place of chlorine depends on several factors, including the quality of the raw water, the ability of the treatment plant to meet various regulations, operational practices, and distribution system characteristics. Chloramines have proven effective in accomplishing:

    • Reducing the formation of THMs and other DBPs
    • Maintaining a detectable residual throughout the distribution system
    • Penetrating the biofilm in the pipeline and reducing the potential for coliform regrowth
    • Killing or inactivating heterotrophic plate count bacteria
    • Killing or inactivating heterotrophic plate count bacteria
    • Reducing taste and odor problems

    Methods for Producing Chloramines

    Three primary methods are used to produce chloramines:

    1. Preammoniation followed by later chlorination-in this method, ammonia is applied at the rapid-mix unit process and chlorine is added downstream at the entrance to the flocculation basins. This approach usually produces lower THM levels than the postammoniation method. Preammoniation is used to form chloramines that does not produce phenolic tastes and odors, but this method may not be as effective as postammoniation for controlling tastes and odors associated with diatoms and anaerobic bacteria in source waters.
    2. Concurrent addition of chlorine and ammonia-in this method, chlorine is applied to the plant influent, and at the same time or immediately thereafter, ammonia is introduced at the rapid-mix unit process. Concurrent chloramination produces the lowest THM levels for the three methods.
    3. Prechlorination/Postammoniation-in this method, chlorine is applied at the head of the plant and a free chlorine residual is maintained throughout the plant processes. Ammonia is added at the plant effluent to produce chloramines. Because of the longer free chlorine contact time, this application method will result in the formation of more THMs, but it may be necessary to use this method to meet the disinfection requirements to the Surface Water Treatment Rule. A major limitation of using chloramine residuals is that chloramines are less effective as a disinfectant than free chlorine residuals. However, chloramine residuals go deeper into the distribution system and last longer than free chlorine residuals.
    Typical chloramines formation in a conventional treatment process.
    Figure \(\PageIndex{1}\): Chloramination Disinfection – Image by the EPA is in the public domain

    When measuring combined chlorine residuals (chloramines) in the field, analyze for total chlorine. Total chlorine is the total concentration of chlorine in water, including the combined chlorine and the free available chlorine. No free chlorine should be present at chlorine to ammonia nitrogen ratios of 3:1 to 5:1. Care must be taken when attempting to measure free chlorine with chloraminated water because the chlorine residual will interfere with the DPD method of measuring free chlorine.

    Chloramination breakpoint curve
    Figure \(\PageIndex{2}\): Breakpoint Curve for Chloramination – Image by Aliciacdiehl is licensed under CC BY-SA 3.0

    In plants where THMs are not a problem, sufficient chlorine to get past breakpoint is added to the raw water. Chlorine residual aids coagulation and algal control, reduces odor problems, and provides sufficient chlorine contact time to effectively kill or inactivate pathogenic organisms. Therefore, the treated water will have a very low chlorine residual, but the residual will be a very effective disinfectant.

    When chlorine is added to water containing ammonia, the ammonia reacts with hypochlorous acid to form monochloramine, dichloramine, and trichloramine. The formation of these chloramines depends on the pH of the solution and the initial chlorine-ammonia ratio.

    At the pH levels usually found in water treatment plants (pH 6.5 to 7.5), monochloramine and dichloramine exist together. At pH levels below 5.5, only dichloramine exists. Below pH 4.0, trichloramine is the only compound found. The mono and dichloramine forms have definite disinfection powers and are of interest in the measurement of chlorine residuals. Dichloramine has a more effective disinfecting power than monochloramine. However, dichoramine is not recommended as a disinfectant because of taste and odor problems. Chlorine reacts with phenolic compounds and salicylic acid to form chlorophenol, which has an intense medicinal odor. This reaction goes much slower in the presence of monochloramine.

    Nitrification

    Nitrification is an important and effective microbial process in the oxidation of ammonia in land and water environments. Two groups of organisms are involved in the nitrification process:

    • Ammonia-oxidizing bacteria, Nitrobacter
    • Nitrite-oxidizing bacteria, Nitrosoma

    When nitrification occurs in chloraminated drinking water, the process may lower the water quality unless the nitrification process reaches completion. Incomplete or partial nitrification causes the production of nitrite from the growth of Nitrobacter bacteria. This nitrite, in turn, rapidly reduces free chlorine and can interfere with the measurement of free chlorine. The end result may be a loss of total chlorine and ammonia and an increase in the concentration of heterotrophic plate count bacteria.

    Factors influencing nitrification include the water temperature, the detention time in the reservoir or distribution system, excess ammonia in the water system, and the chloramine concentration used. Conditions that are most likely to lead to nitrification when using chloramines are a pH of 7.5 to 8.5, a water temperature of 77 to 86oF, a free ammonia concentration in the water, and a dark environment. The danger in allowing nitrification episodes to occur is that the operator may be left with very low or no total chlorine residual. Total chlorine residual is the total concentration of chlorine in water, including the combined chlorine and the free available chlorine.

    The Surface Water Treatment Rule requires the disinfection of all surface water supply systems as protection against exposure to viruses, bacteria, and Giardia.

    Drinking water regulations are constantly changing. The Interim Enhanced Surface Water Rule and the Disinfectant/Disinfection By-products Rule were passed in 1998 and further modifications of these rules have been developed. The goal of these rules was to increase the public protection form illness caused by Cryptosporidum, to limit the amount of certain potentially harmful disinfection byproducts that may remain in drinking water after treatment.

    Review Questions

    1. Describe chloramination.
    2. Outline the uses of chloramination.
    3. Explain the formation of chloramines.

    Test Questions

    1. Chloramine is toxic to fish and amphibians. Chloramine, like chlorine, comes in direct contact with their bloodstream through their gills, and it must be removed from water added to aquariums and fish ponds. It must also be removed from water prior to use in _____________
      1. Boilers
      2. Metal plating operations
      3. Dialysis
      4. Oil refining
    2. Chloramine is generally considered a problem in ______ because it can react with and change some of the natural plant flavors. It may slow or alter the yeast activity.
      1. Dialysis
      2. Brewing beer
      3. Paper manufacturing
      4. Commercial baking
    3. Recent discussion concerning chloramine has focused on the disinfection byproduct _______.
      1. Chlorite
      2. THM
      3. Bromate
      4. NDMA
    4. Monochloramine and dichloramine forms of chloramines have definite disinfection powers and are of interest in the measurement of chlorine residuals. ________ has a more effective disinfecting power.
      1. Monochloramine
      2. Trichloramine
      3. Dichloramine
      4. N-nitrosodimethylamine
    5. _______ ammonia-oxidizing bacteria.
      1. Nitrobacter
      2. E. coli
      3. Cryptosporidium
      4. Nitrosoma
    6. _______ nitrite-oxidizing bacteria.
      1. Nitrobacter
      2. E. coli
      3. Cryptosporidium
      4. Nitrosoma
    7. When nitrification occurs in chloraminated drinking water, the process may lower the water quality unless the nitrification process reaches completion. Incomplete or partial nitrification causes the production of _____ from the growth of Nitrobacter bacteria. This, in turn, rapidly reduces free chlorine and can interfere with the measurement of free chlorine.
      1. Nitrate
      2. Nitrite
      3. Ammonia
      4. NDMA
    8. At very high levels, NDMA may cause serious human health problems, such as _______.
      1. Malformation of the brain
      2. Gastrointestinal disruptions
      3. Liver disease
      4. Kidney disorders
    9. _________ is the total concentration of chlorine in water, including the combined chlorine and the free available chlorine.
      1. Monochloramine
      2. Chlorine residual
      3. Breakpoint chlorination
      4. Total chlorine

    This page titled 1.4: Chloramination is shared under a CC BY license and was authored, remixed, and/or curated by John Rowe (ZTC Textbooks) .

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