6 Methods Of The Chlorination Of Water

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The chlorination of water typically involves six main steps/methods. These include plain chlorination, pre-chlorination, post-chlorination, double or multiple chlorinations, break-point chlorination, and super chlorination. Depending on the use of the water will determine which chlorination method is best. Some industries such as drinking water, may require more than one method of chlorinating the water. 

Many microorganisms are found in water sources such as lakes, rivers, and even groundwater, and while not every microorganism can pose a health risk to humans, there are a few that can cause diseases. These microorganisms are known as pathogens. Pathogens in water can easily be transported via drinking water systems, resulting in waterborne diseases to people who drink the water. 

To prevent waterborne diseases there are a range of disinfection processes to inactivate these harmful pathogens. In addition to water treatment processes such as sedimentation, coagulation, etc, chlorination is a critical step in creating safe water for public use. 

In this article, we will look at why chlorination is used in water treatment and the different steps to ensure water is safe for use. 

The History Behind Chlorination

Chlorination techniques were developed in the late 19th and early 20th century. The first large-scale chlorination system in the United States was created in 1908 at the Jersey City Works.

Over time, more water systems took on chlorination water treatment methods, resulting in a decrease in the number of waterborne disease cases. It was from there that health professionals announced water chlorination as one of the most vital advances in the public health field. 

The Importance Of Chlorinating Water

There has been extensive research and studies into the importance of using free chlorine as a disinfectant in water treatment plants. The main advantage is the ability to kill bacteria and viruses, yet, it is important to note that chlorine is not able to inactivate all microbes in water. For example, chlorine can disinfect the water but it cannot purify it. 

Therefore, microorganisms such as cryptosporidium and protozoan cysts can live in the water for days after treatment. This is because they have a resistant cell wall, so the chlorine is unable to disrupt the cell structure and DNA activity inside the microorganism, this is how chlorine can raise the pH of water

In occasions where cryptosporidium and protozoan cysts are not a major issue, chlorination is still a fantastic disinfection method as it is cheap but extremely effective at disinfecting many water contaminants like E.coli.

Chlorination processes are also simple to implement in water treatment plants compared to other treatment methods. So, in emergencies, chlorine acts as an effective method to eliminate water teeming with pathogens. Emergencies can be anything from a faulty water filter to raw water accidentally mixing with treated water. 

Methods To Chlorinate Water 

There are six main processes associated with the chlorination of water:

  1. Plain Chlorination
  2. Pre-Chlorination
  3. Post-Chlorination
  4. Double or Multiple Chlorinations
  5. Break Point Chlorination
  6. Super Chlorination

Plain Chlorination

When solely chlorine is used in disinfection, we call it plain chlorination, as the water is free from suspended material without any previous water treatment. Plain chlorination is common if the water is clear and no additional water treatment steps are required to remove sediment and particulates.

Therefore, plain chlorination aims to simply disinfect the water, successfully neutralizing or demobilizing any microorganisms that could be harmful. 

Pre-Chlorination

Pre-chlorination processes are required to chlorinate untreated raw water before further water treatments. This serves a double purpose as it helps to enhance coagulation by oxidizing particular compounds, making it easier for the formation of bigger and settleable floc particles during the coagulation and flocculation stages. The second part of pre-chlorination helps to eliminate poor taste, color, and odor by oxidizing organic compounds associated with this undesired water quality. 

Post-Chlorination

After all water treatment stages (filtration, coagulation, sedimentation, disinfection) have finished, chlorine is used to treat the water in post-chlorination. 

The purpose is to provide one last chlorine dose in the water to preserve a residual disinfectant in every part of the distribution system. This guarantees the breaking up of any microorganisms left behind and safeguards the water against potential contamination.

The post-chlorination process generally requires a dosage of 0.25 to 5.0 mg/L of chlorine to reach a residual chlorine concentration of 0.1 to 0.2 mg/L. 

Double/Multiple Chlorinations

Double/multiple chlorinations incorporate pre-chlorination methods and post-chlorination methods. This is required when the untreated water is extremely contaminated and the water contains a large amount of bacterial life. 

Using both these chlorination methods addresses initial water contamination and residual disinfection. It also ensures that extremely polluted water will undergo comprehensive treatment to ensure that it is safe. 

Break-Point Chlorination

This technique is used to establish the greatest amount of chlorine that is needed to achieve the desired level of remaining chlorine in the water. By recognizing the breakpoint, treatment facilities can find the precise amount of chlorine needed to ensure that disinfection has been effective. It also prevents unnecessary chlorine use in the water, as too much chlorine can result in undesirable disinfection byproducts.

Superchlorination

As the name suggests, superchlorination focuses on the intentional addition of chlorine to the water past the recommended level, or breakpoint stage. This chlorination method is used at the end of the filtration process. 

Superchlorination is common when treating water that has had an eruption of waterborne diseases or if an extreme level of disinfection is required. 

If performing superchlorination, it is important to understand that it is critical to get rid of excess chlorine using a suitable dechlorination method before the water is used for consumption. This extra precaution will stop any potential adverse effects by using high levels of chlorine in the water. 

Pros Of Chlorination Of Water

The advantages of chlorination are:

  • Eliminates and eradicates harmful and pathogenic microorganisms in the water
  • Cost-effective treatment
  • It guards against waterborne diseases
  • It sustains water quality throughout distribution
  • Offers lasting protective effects
  • It is a straightforward procedure 

Cons Of Chlorination Of Water

While there are many advantages to using chlorine in water treatment, there are some disadvantages that you should know about. 

  • Chlorine may cause undesirable taste and odor to the water
  • The formation of harmful disinfection byproducts is possible
  • Certain people may experience allergic reactions to the chlorine in water
  • Chlorine can corrode specific materials like stainless steel and nickel-based alloys, potentially impacting equipment performance
  • Chlorine cannot be effective against all parasites and viruses

How To Measure Chlorine Levels In Water?

Measuring chlorine levels in water is essential during the different methods of chlorination. It is not only important for safety, but it also measures effectiveness. 

The most common way to measure chlorine in water is the use of a chlorine test kit or portable chlorine meter. These kits use colorimetric or titration methods to determine the chlorine concentration or the concentration of free-chlorine molecules. 

Whichever you choose, the main focus is to regularly monitor the chlorine levels to ensure water quality and safety standards are followed. 

Alternative Methods To Disinfect Water With Chlorine 

Although chlorine has been widely used since the 19th century, there are other ways to effectively disinfect water. Many alternative methods have emerged due to concerns with using chlorine such as the negative impact on the environment or the harmful by-products. 

Alternative methods can offer other effective disinfection methods, these include the following. 

Ultraviolet (UV) Disinfection

This involves exposing the water to UV light to destroy the DNA of microorganisms, preventing them from reproducing. UV water treatment is effective in removing pathogens and protozoa in water without the need for chemical treatment. This is commonly used in municipal water treatment plants and smaller-scale water systems in homes and offices/businesses.

Ozone Treatment

Ozone (O3) is an extremely powerful oxidizing agent known for breaking down organic molecules and killing microorganisms. This is also a very useful method to not only disinfect the water, but also to remove odor, taste, and color issues in the water. Ozone treatment is commonly used in water treatment plants. 

Chloramine Disinfection

Chloramine is a compound of chlorine and ammonia and is widely used as an alternative to free chlorine for water disinfection processes as it is less reactive than chlorine. 

Chloramine is commonly used when a longer-lasting disinfectant residual is required such as in water distribution systems or when the operator needs to control biofilm growth. 

Hydrogen Peroxide

Hydrogen peroxide is a strong oxidizing agent that disinfects water. You are probably already familiar with it in your household cleaning products such as bleach. In water disinfection processes, the hydrogen peroxide reacts with organic matter and microbial cells to break them down.

Silver Ionization

Less commonly used, yet still effective, is silver ionization which involves using silver ions that have microbial properties to kill bacteria, viruses, and other harmful pathogens in the water. 

You can find silver ionization methods in recreational water facilities, cooling towers, and water systems that require highly accurate microbial control. 

Summary

Chlorination is a critical process in treating water to safeguard public health. Chlorine is a successful method to disinfect water that contains harmful microorganisms. 

Although chlorine has been widely used since the 19th century, there are some challenges with disinfection by-products and poor odor/taste, opening the door to alternative methods of water disinfection.

Should you have any questions regarding the chlorination of water or what method is recommended for your water use, do not hesitate to contact the world-class team at Atlas Scientific.

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