WHAT IS CHLORINATION

WHAT IS CHLORINATION?

Microorganisms can be found in raw water from rivers, lakes and groundwater. While not all microorganisms are harmful to human health, there are some that may cause diseases in humans. These are called pathogens. Pathogens present in water can be transmitted through a drinking water distribution system, causing waterborne disease in those who consume it.

 

In order to combat waterborne diseases, different disinfection methods are used to inactivate pathogens. Along with other water treatment processes such as coagulation, sedimentation, and filtration, chlorination creates water that is safe for public consumption.

Chlorination is one of many methods that can be used to disinfect water. This method was first used over a century ago, and is still used today. It is a chemical disinfection method that uses various types of chlorine or chlorine-containing substances for the oxidation and

Disinfection of what will be the potable water source.

THE HISTORY OF CHLORINATION

Chlorine was first discovered in Sweden in 1744. At that time, people believed that odoursfrom the water were responsible for transmitting diseases. In 1835, chlorine was used to remove odours from the water, but it wasn't until 1890 that chlorine was found to be an effective tool for disinfecting; a way to reduce the amount of disease transmitted through water. With this new find, chlorination began in Great Britain and then expanded to the United States in 1908 and Canada by 1917. Today, chlorination is the most popular method of disinfection and is used for water treatment all over the world.

WHY DO WE CHLORINATE OUR WATER?

A large amount of research and many studies have been conducted to ensure success in new treatment plants using chlorine as a disinfectant. A leading advantage of chlorination is that it has proven effective against bacteria and viruses; however, it cannot inactivate all microbes.

Some protozoan cysts are resistant to the effects of chlorine.In cases where protozoan cysts are not a major concern, chlorination is a good disinfection method to use because it is inexpensive yet effective in disinfecting many other possibly present contaminants. The chlorination process is also fairly easy to implement, when compared to other water treatment methods. It is an effective method in water emergency situations as it can eliminate an overload of pathogens relatively quickly. An emergency watersituation can be anything from a filter breakdown to a mixing of treated and raw water.

HOW DOES CHLORINE INACTIVATE MICROORGANISMS?

Chlorine inactivates a microorganism by damaging its cell membrane. Once the cell membrane is weakened, the chlorine can enter the cell and disrupt cell respiration and DNA activity (two processes that are necessary for cell survival).

WHEN/HOW DO WE CHLORINATE OUR WATERS?

Chlorination can be done at any time/point throughout the water treatment process - there is not one specific time when chlorine must be added. Each point of chlorine application will subsequently control a different water contaminant concern, thus offering a complete spectrum of treatment from the time the water enters the treatment facility to the time it leaves.

Pre-chlorination is when chlorine is applied to the water almost immediately after it enters the treatment facility. In the pre-chlorination step, the chlorine is usually added directly to the raw water (the untreated water entering the treatment facility), or added in the flash mixer (a mixing machine that ensures quick, uniform dispersion of the chlorine). Chlorine is added to raw water to eliminate algae and other forms of aquatic life from the water so they won’t cause problems in the later stages of water treatment. Pre-chlorination in the flash mixer is found to remove tastes and odours, and control biological growth throughout the watertreatment system, thus preventing growth in the sedimentation tanks (where solids are

Removed from the water by gravity settling) and the filtration media (the filters through which the water passes after sitting in the sedimentation tanks). The addition of chlorine will also oxidize any iron, manganese and/or hydrogen sulphide that are present, so that they too can be removed in the sedimentation and filtration steps.

Disinfection can also be done just prior to filtration and after sedimentation. This would control the biological growth, remove iron and manganese, remove taste and odours, control algae growth, and remove the colour from the water. This will not decrease the amount of biological growth in the sedimentation cells.

Chlorination may also be done as the final step in the treatment process, which is when it is usually done in most treatment plants. The main objective of this chlorine addition is to disinfect the water and maintain chlorine residuals that will remain in the water as it travels through the distribution system. Chlorinating filtered water is more economical because a lower CT value is required. This is a combination of the concentration (C) and contact time (T). The CT concept is discussed later on in this fact sheet. By the time the water has been through sedimentation and filtration, a lot of the unwanted organisms have been removed,

And as a result, less chlorine and a shorter contact time is required to achieve the sameeffectiveness. To support and maintain the chlorine residual, a process called re-chlorination is sometimes done within the distribution system. This is done to ensure proper chlorine residual levels are maintained throughout the distribution system.

BREAKPOINT CHLORINATION

Break point chlorination is adding enough chlorine to eliminate problems associated with combined chlorine. Specifically, breakpoint chlorination is the point at which enough free chlorine is added to break the molecular bonds; specifically the combined chlorine molecules, ammonia or nitrogen compounds. It takes a ratio of chlorine to ammonia atoms of 7.6 to 1 to reach breakpoint, other contaminants (i.e. bacteria, algae) are also present that must be The information is mostly obtained from the Indiana State Department of HealthPage 2of 4

Oxidized, so 10 times the amount of combined chlorine must be added. When sufficient free chlorine (FC) is added to water, the inorganic chloramines are converted to dichloramine, then to nitrogen trichloride, and then to nitrogen gas. Any excess chlori leftover will become the chlorine residual (FC).

WHAT ARE CHLORAMINES?

Chloramines are disinfectants used to treat drinking water.

                        Chloramines are most commonly formed when ammonia is added to chlorine to treat drinking water.

                        The most typical purpose of chloramines is to protect water quality as it moves through pipes.

                        Chloramines provide long-lasting protection as they do not break down quickly in water pipes.

THE DIFFERENT TYPES OF CHLORAMINES ARE MONOCHLORAMINE, DICHLORAMINE, TRICHLORAMINE, AND ORGANIC CHLORAMINES.

                        When chloramines are used to disinfect drinking water, monochloramine is the most common form.

                        Dichloramine, trichloramine, and organic chloramines1, 2 are produced when treating drinking water but at much lower levels than monochloramine.

                        Trichloramines1 are typically associated with disinfected water used in swimming pools.

The Environmental Protection Agency regulates the safe use of chloramines in

Drinking water.

                        EPA requires water utilities to meet strict health standards when using chloramines to treat water.

                        EPA chloramines regulations are based on the average concentration of chloramines found in a water system over time.

                        EPA regulates certain chemicals formed when chloramines react with natural organic matter4 in water

HOW TO CALCULATE CHLORINE DOZE

Water treatment plants convert fresh water into potable drinking water, removing contaminants and killing bacteria that are harmful when ingested. A common method of cleaning the water being processed is with the use of chlorine. When using chlorine in the water it is important to carefully monitor the amount used -- to ensure enough chlorine is infused to kill harmful bacteria -- while not over-chlorinating the water and making it dangerous. This is performed by applying a basic formula to the treatment facility's water flow data.

DETERMINATION POUNDS PER DAY

Check the flow rate of the facility in million gallons per day (MGD). For example, a facility that processes 1,500,000 gallons of water per day, the MGD glow is 1.5.

Multiply the MGD by 8.34 lbs per gallon. In the example, the result would be 12.51.

Multiply the result by the desired concentration of chlorine in milligrams per liter. For the example, a desired concentration of 4 milligrams per liter

would be multiplied by 12.51 to yield a result of 50 pounds of chlorine per day.

FINDING THE CONCENTRATION OF A SOLUTION

Check the flow rate of the facility in million gallons per day (MGD). For example, a facility that processes 3,000,000 gallons of water per day, the MGD glow is 3.

Determine the amount of chlorine being added to the water each day. For the example, assume the facility is using 100 pounds of chlorine per day.

Divide the daily chlorine input by the MGD flow of the facility. In the example, the result would yield 33.33.

Divide the result by 8.34 pounds per gallon to find the chlorine concentration. In the example, the concentration is 4 milligrams per liter.

DETERMINING CHLORINE DEMAND FOR YOUR WATER SYSTEM

It is imperative that water systems identify their chlorine demand so that free chlorine dosage can be minimized at the plant and to ensure chlorine residuals can be maintained in the distribution system at the 0.20 mg/l free chlorine or 0.60 mg/l chloramine levels that are regulatory requirements.

Many systems that have performed DBP analysis on their finished water at the plant, find that after implementing the controls described above, that DBP produced at the plant are 25% or less than those produced in the distribution system. By maintaining excessive free chlorine residuals in the distribution system, the reaction rates with organic material will be increased and more disinfection by-products will be produced. Conversely with chloramine, if significant excess residual is not maintained, the chloramine will have a tendency to breakdown leading to formation of disinfection by-products, slime growth and nitrification. It is important that systems check the concentration both at the entrance to the distribution system and at the regulatory monitoring point for purposes of targeting

The most significant problems.

The substances that cause disinfectant demand are indicative of the source water quality and are also are the compounds that typically cause water quality customer complaints.

Most source waters contain a variety of both inorganic and organic contaminants whose chlorine demand can be identified with a simple jar test without knowledge of the types of concentrations of the contaminants. The procedures illustrated below can be quickly set up and used to give a good approximation of the chlorine demand. Limiting free chlorine demand to that necessary to maintain the required residual is the most effective method of controlling disinfection by-product production.

CONCLUSION

Chlorination is a very popular method of water disinfection that has been used for many years. It has shown to be effective for killing bacteria and viruses, but not for some protozoan cysts. With the concern about trihalomethanes, a carcinogenic disinfection byproduct, many communities have become hesitant in the continuation of this process.

Although chlorination does have some drawbacks, it continues to be the most popular, dependable, and cost-effective method of water disinfection.