What is water treatment calcium hypochlorite and Why Do We Use Them?

Every year waterborne disease outbreaks occur because of public water distribution system deficiencies. A significant number of these outbreaks are caused by broken water mains or contamination of water mains during construction or repair. Disease outbreaks emphasize the importance of using proper procedures and methods when repairing water mains.

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To prevent waterborne disease outbreaks, every supplier of water for a public water system must disinfect all newly constructed or repaired water distribution mains by the methods and procedures proposed by the American Water Works Association (AWWA) standards. Calcium hypochlorite granules shall disinfect new water mains before they are placed in service.

Disinfection of New Water Mains by Calcium Hypochlorite Granules

The use of calcium hypochlorite for disinfection is a relatively simple and cost-effective process that does not require extensive technical expertise. It can handle supply systems of varying sizes by altering dosing systems or storage for chemical contact. The calcium hypochlorite granules are a powerful disinfectant; it kills almost 99.9 percent of all germs (bacteria, viruses, and mildew) and makes the water flowing through potable water lines clean and healthy.

How is Calcium Hypochlorite Applied to New Water Mains?

AWWA C651-14 standard can be used as a guide for the preparation of water mains, application of calcium hypochlorite, sampling, and testing for the presence of coliform bacteria. Calcium hypochlorite conforming to AWWA B300 is available in granular form and must contain approximately 65 percent available chlorine by weight. The material should be stored in a cool, dry, and dark environment to curtail its deterioration. Disinfection of water mains should be done by contractors that install underground water pipelines with calcium hypochlorite as per AWWA standards. Water testing would then be performed in the water utility lab or by a third-party testing provider.

For new mains, sets of samples shall be collected after every 1,200 feet (370 m) of the new water main, and one set from the end of the pipeline and at least one from each branch longer than one pipe length. Disease outbreaks emphasize the importance of using proper procedures and methods when disinfecting water mains using calcium hypochlorite granules to ensure safe and clean water passage through potable water lines.

Methods of Disinfection by Calcium Hypochlorite

The Tablet Method is generally used for disinfection of water mains of 12 inch and smaller diameter mains. The tablet method consists of placing calcium hypochlorite granules or tablets in the water main during installation and then filling the main with potable water to create a calcium hypochlorite solution.

This method may be used only if the pipes and appurtenances are kept clean and dry during installation. The required number of tablets are placed on the inside top of each joint and held in place by approved mastic. The main is then filled with water at a velocity of less than 1 foot per second, and the water is left in the main for at least 24 hours before flushing.

Placement of Calcium Hypochlorite Tablets During Construction

Calcium hypochlorite tablets (5-grams) shall be placed in the upstream end of each section of the pipe to be disinfected, including branch lines. Also, at least one tablet shall be placed in each hydrant outlet and other appurtenances. The chlorinated water shall remain in the pipeline for at least 24 hours. If the water temperature is less than 41°F (5°C), the water shall stay in the pipe for at least 48 hours. The table below shows the number of tablets required for commonly used sizes of pipe.

Number of 5-g calcium hypochlorite tablets for a dose of 25 mg/L

The Slug Method of Chlorination is used for large diameter water mains. It comprises moving a column of highly concentrated calcium hypochlorite water solution (at least 300 mg./L) along with the interior of the pipe with a contact time of a minimum of three hours with the pipe wall. The flushed water should be visually clear and have typical system chlorine residual.

For very-large-diameter pipe (where personnel may safely enter the pipe), instead of flushing following disinfection, the pipe's interior at the repair site may be cleaned by a sweeping and high-pressure wash using potable water before disinfection. Standing water and debris from the cleaning must be removed from the pipe before disinfection. The affected pipe shall be disinfected by swabbing or spraying with a minimum of 1 percent chlorine solution.

After following the appropriate methods above, prior to returning the pipe to service, the disinfection procedure's efficiency shall be verified by testing for the absence of coliform bacteria. If allowed by local regulations, the pipeline may be reverted to limited service before obtaining bacteriological results with proper notification of the affected customers.

Final Flushing

Final flushing can be accomplished, and chlorine residuals checked to determine that the heavily chlorinated water has been removed from the pipeline. After final flushing, bacteriological tests are performed in accordance with state and local regulations to ensure that no coliform organisms are present. 

After the applicable retention period, heavily chlorinated water should not remain in constant contact with the pipe to prevent damage to the pipe lining. To prevent corrosion damage to the pipe itself, the heavily chlorinated water shall be flushed from the main fittings, valves, and branches until chlorine measurements show that the concentration in the water leaving the main is no higher than that generally prevailing in the distribution system or that is acceptable for domestic use.

PLEASE NOTE: When flushing out the chlorinated water, caution should be taken to provide environmentally acceptable disposal.  

ANSI/AWWA 651, the updated Disinfection of Water Mains standard, seeks to clarify steps to take depending on the nature of the work. Given the wide range of projects and repairs, these updates accommodate the variety of conditions that come across and provide a means to assess the risk and identify the appropriate level of disinfection and sampling before any outbreak. Strict compliance with the guideline provided by AWWA standards results in the complete disinfection of the water main and availability of clean water for domestic purposes.

For more on safe drinking water see the list of Iron Strong Blogs below:

• Safe Drinking Water – How Do We Ensure the Highest Standards? by Jerry Regula
• Do You Have an Iron Deficiency? – Considering Health Effects of Pipe Material Selection by Roy Mundy
• How to Protect Water Quality from Permeation Due to Contaminated Soils by John Johnson
• Got Certification? Fabricated Ductile Iron Pipe and NSF/ANSI 61 by Dan Henrie

Need Assistance with Your Waterworks Project?

If you have any questions regarding this topic or anything Ductile iron pipe-related, be sure to reach out to your local McWane Ductile representative. We have team members who've managed small and large water utility systems, served in engineering consulting firms, and bring decades of experience in solving field issues involving pipeline construction and operation. From design to submittal, to installation, we strive to provide education and assistance to water professionals throughout the water and wastewater industry.

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Bob Hartzel is the Senior Sales Representative for McWane Ductile, covering the eastern Pennsylvania sales territory.
Bob began his career with the McWane Company in . He started as a Sales Representative covering eastern Pennsylvania. He was later promoted to District Manager of the Mid-Atlantic Territory in . As D.M., he managed sales in PA, NJ, DE, MD, and D.C., while still covering eastern Pennsylvania. In early , his role changed to Senior Sales Representative, responsible for sales in eastern Pennsylvania only.
“I enjoy the relationships I have developed with my customers over the years. Those relationships have become friendships. I enjoy assisting them with troubleshooting issues as well as providing insights to help them meet their goals while providing outstanding customer service,” says Hartzel.
Bob is a graduate of Slippery Rock University with a B.S. in Physical Education with an emphasis in Sport Management. Bob has been a member of the local AWWA, WWOAP Associations, and various contractor associations over the years.
In his spare time, Bob enjoys weight training and exercise, as well as hunting and fishing. He also volunteers at a local food bank handing out Thanksgiving meals.
Bob’s favorite quote: “The only way to do great work is to love what you do.” – Steve Jobs

What is calcium hypochlorite?

This compound is often used as a bleaching agent and disinfectant, and has a variety of uses, including disinfection, sterilization, and bleaching. Calcium hypochlorite is also widely used in the field of water treatment to disinfect and purify water and is a wastewater chemical used to remove bacteria, viruses, and organic matter from water.

Application Of Calcium Hypochlorite In Water Treatment

1. Disinfection of water: Calcium hypochlorite can be used to disinfect drinking water, swimming pool water, industrial water, and disposal waste water. It can effectively kill bacteria, viruses, parasites, and other microorganisms in the water, thus ensuring the safety of water quality.
2. Remove odor and organic matter: Calcium hypochlorite can oxidize organic matter and odor substances in water, which helps to remove pollutants in water and improve the quality and taste of water.
3. Bleaching and color removal: It is also used as a bleaching agent, which is effective in removing colors and impurities when treating water sources that contain colors or stains.
4. Alternative to chlorine: Calcium hypochlorite is often used as an alternative to chlorine because it is easier to control and store during use and is relatively safer to handle.
5. Environmental friendliness: The use of calcium hypochlorite in water treatment processes is generally considered to have a low environmental impact compared to some other oxidizing agents.

Difference Between Calcium Hypochlorite And Sodium Hypochlorite

Calcium hypochlorite (Ca(ClO)₂) and sodium hypochlorite (NaClO) are two chemical substances that, although they both contain hypochlorite ions (ClO-), have some differences in chemical properties and uses:

Composition: Calcium hypochlorite is the calcium salt of hypochlorous acid, while sodium hypochlorite is the sodium salt of hypochlorous acid.

Physical properties: Calcium hypochlorite is often found in solid form, usually in powder or crystal form, while sodium hypochlorite is usually found in solid form, more commonly in powder or crystal form.

Uses: Although they are both common oxidizers and disinfectants, calcium hypochlorite is sometimes chosen for specific occasions, especially when calcium ions are needed, due to the presence of calcium ions in calcium hypochlorite.

Solubility: When dissolved in water, calcium hypochlorite releases calcium and hypochlorite ions, while sodium hypochlorite releases sodium and hypochlorite ions.

In the field of water treatment and disinfection, both substances can be used as disinfectants for similar purposes, but when it comes to specific applications, the choice of which one to use will be based on specific needs and conditions.

Working Principle Of Calcium Hypochlorite Water Treatment

Pretreatment: First of all, you can add calcium hypochlorite to the raw sewage to achieve pre-treatment, and then carry out preliminary solid-liquid separation and filtration of the sewage to remove most of the suspended solids and solid particles, to reduce the burden of the subsequent treatment steps. In carrying out the preliminary removal, the kuosi screw screen can be used to realize efficient solid-liquid separation for preliminary screening.

Calcium hypochlorite dosing: The appropriate amount of calcium hypochlorite solution is then dosed into the wastewater. The calcium hypochlorite solution will release hypochlorite ions, which kill bacteria and oxidize organic matter.

Mixing and residence time: The mixed calcium hypochlorite solution is mixed thoroughly with the wastewater to ensure that the calcium hypochlorite comes into full contact with the microorganisms and organic matter in the wastewater to achieve the effect of disinfection and oxidation. A certain residence time is needed to ensure that the reaction is sufficient.

Advantages Of Calcium Hypochlorite In Water Treatment

Calcium hypochlorite, as a commonly used disinfectant, has a number of advantages in water treatment over other disinfection methods (e.g., ozone, sodium hypochlorite) that may include.

Stability: Can be stored and used for long periods under proper conditions, ozone requires more equipment and controls for preparation and storage, while sodium hypochlorite requires special environments and packaging to avoid failure during storage and transportation.

Convenience: A solution can be prepared by dissolving solid calcium hypochlorite and adding it to water. Ozone needs to be prepared in a specialized ozone generator, while sodium hypochlorite needs to be diluted and properly controlled for application.

Cost-effectiveness: Calcium hypochlorite is a relatively affordable disinfectant with a relatively low cost of preparation and use.
Sterilizing effectiveness: Calcium hypochlorite is effective in killing microorganisms, including bacteria, viruses, and parasites, at appropriate concentrations. This disinfectant is usually able to achieve good bactericidal efficacy in a relatively short contact time.

Calcium Hypochlorite Mixing Precautions

Calcium hypochlorite can have dangerous chemical reactions when mixed with certain chemicals, so avoid mixing it with the following chemicals:

• Organic matter: Calcium hypochlorite should not be mixed with organic matter, because organic matter may degrade calcium hypochlorite, affect its disinfection effect, or even produce toxic gas.
• Reducing agents: Avoid mixing with reducing agents (e.g. sulfuric acid, sulfurous acid, sulfide, etc.) because the reducing agents may neutralize the calcium hypochlorite, leading to its failure or danger.
• Acids: Mixing with acids (e.g. hydrochloric acid, sulfuric acid, etc.) may trigger exothermic reactions and produce harmful gases, and acids will reduce the disinfection effect of calcium hypochlorite.

Summary

Calcium hypochlorite is a commonly used disinfectant and oxidizer, commonly used in water treatment and effluent treatment, can achieve a good disinfection effect in a relatively short period, but the use of need to follow safe operating procedures, pay attention to safety protection.

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