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Water chlorination is a chemical process that consists of the controlled addition of chlorine in its various forms such as gas, liquid or chlorinated compounds. Chlorine is a powerful disinfecting agent that is widely used in the treatment of drinking water, swimming pool water, wastewater and other similar applications. The main purpose of chlorination is to eliminate or inactivate pathogenic microorganisms, such as bacteria, viruses and parasites, that may be present in water and that could cause disease if ingested.

Chlorination for water purification

Chlorine is added to water in controlled amounts to kill bacteria, viruses and other organisms that may be present in the water. Although this method is highly effective in eliminating pathogens, chlorine can generate by-products that may be undesirable or even potentially harmful to human health.

To eliminate these residues and chlorine by-products, activated carbon purification is required in the treatment process. Activated carbon is a porous material that has the ability to adsorb a wide variety of organic and inorganic compounds. In this case, the activated carbon destroys the chlorine, as well as the by-products, by a chemical reaction where the activated carbon reduces the chlorine molecule into hydrochloric acid at a very low concentration, almost undetectable, which improves water quality and eliminates unwanted tastes, odors and contaminants.

After filtration, additional steps are implemented to ensure complete removal of pathogens and by-products. One of these steps is the application of ultraviolet (UV) light or ozone. Ultraviolet light disinfects water by damaging the genetic material of microorganisms, preventing them from reproducing and causing disease. On the other hand, ozone is a powerful oxidizing agent that decomposes organic compounds and eliminates pathogens in the water and does not generate residues.

Water chlorination methods

There are several chlorination methods that vary depending on the type of chlorine used and the dosing process.

Gaseous chlorine: Chlorine gas (Cl₂) is introduced directly into the water in gaseous form. This method can be effective, but requires careful handling due to the toxicity of the gas and the need for specialized equipment, since chlorine gas can affect the respiratory system.

Sodium hypochlorite: Sodium hypochlorite (NaClO) is a liquid or solid compound containing inorganic salt composed of a sodium atom (Na), a chlorine atom (Cl) and an oxygen atom (O). It is added to water to release chlorine and hypochlorite ions, which act as disinfectants.

Chlorine tablets: These are solid forms of chlorine that dissolve slowly in water, gradually releasing chlorine for water disinfection. Chlorine tablets or tablets used in water chlorination are generally composed of calcium hypochlorite (Ca(ClO)₂) or sodium trichloroisocyanurate (NaCl(C₃N₃O₃)). These compounds contain and gradually release chlorine into the water to disinfect it.

Chloramination: Instead of using gaseous chlorine, chloramines can be formed by reacting chlorine with ammonia. Chloramines are more stable disinfectants and are used in some water treatment systems.

How does chlorination work?

Each of the chlorination methods has its own way of introducing chlorine into the water and releasing chlorine compounds that act as disinfectants:

1.- Chlorine gas:

In the gaseous chlorine method, chlorine (Cl₂) is introduced directly into the water in the form of gas. Once in water, chlorine dissolves and reacts with water to form hypochlorous acid (HClO) and hydrochloric acid (HCl):

Cl₂ + H₂O → HClO + HCl

Hypochlorous acid (HClO) is the effective disinfecting agent in this process. It has the ability to penetrate the cell walls of pathogenic microorganisms, disrupting their functions and damaging their cellular components, resulting in the inactivation and death of the microorganisms.

2.- Sodium hypochlorite:

Sodium hypochlorite (NaClO) is the most common form of water chlorination, a liquid or solid solution containing chlorine ions (Cl-) and hypochlorite ions (ClO-). When added to water, it dissociates into ions:

NaClO → Na⁺ + ClO-

The hypochlorite (ClO-) and chlorine (Cl-) ions present in the solution act as disinfecting agents. The hypochlorite ions attack and oxidize the cellular components of the microorganisms, destroying them in the process.

3.- Chlorine tablets or tablets:

Chlorination tablets are composed of calcium hypochlorite (Ca(ClO)₂) which in contact with water separates into hypochlorite (ClO-) and calcium ions (Ca²⁺):

Ca(ClO)₂ → Ca²⁺ + 2 ClO-

Hypochlorite ions (ClO-) are those with disinfectant and oxidizing properties, acting in a similar way to sodium hypochlorite.

While other tablets may be made of Sodium Trichloroisocyanurate (NaCl(C₃N₃O₃)) which during dissolution in water dissociates into sodium ions (Na⁺), chlorine ions (Cl-), cyanurate ions (C₃N₃O₃O₃-) and hypochlorous acid (HClO):

NaCl(C₃N₃O₃O₃) + H₂O → Na⁺ + Cl- + C₃N₃O₃O₃- + HClO

Both chlorine ion (Cl-) and hypochlorous acid (HClO) contribute to disinfection by reacting with microorganisms, thanks to their oxidative properties. However, hypochlorous acid (HClO) is a more active and stronger form of chlorine in terms of disinfection.

4.- Chloramination:

Chloramines are more stable chemical disinfectants than free chlorine.

Chloramination involves the formation of different types of chloramines, such as monochloramine (NH₂Cl), dichloramine (NHCl₂) and trichloramine (NCl₃).

These chloramines are formed when chlorine reacts with ammonia (NH₃) or ammonium compounds (NH₄⁺) in chlorinated water. Each of these chloramines has disinfectant properties and chemical stability, which makes them useful in water treatment.

A chloramine is a by-product of the action of chlorine in water, especially in the presence of organic matter and ammonia. These by-products are known as N-chloramines and can vary in their composition and disinfectant capacity.

Chloramines are also commonly used as oxidants in water disinfection with a lower oxidation potential than chlorine. Chloramines are particularly useful as oxidants because they do not react with organic and inorganic matter in the water in the same way as free chlorine, which allows a longer duration of disinfectant effect without generating toxic by-products.

There are three main types of chloramines: monochloramine, dichloramine and trichloramine. Monochloramine is the type most commonly used in water disinfection and is generally more effective than free chlorine as a disinfecting agent. Dichloramine and trichloramine are less common and are often produced as by-products of water disinfection by chloramination.

It is important to note that the use of chloramines in water disinfection can have some undesirable side effects. For example, chloramines can generate an unpleasant odor and taste in the water and can irritate the respiratory tract in people who are sensitive or have respiratory problems. In addition, chloramines can generate additional disinfection by-products, which in some cases can be toxic or carcinogenic. For this reason, it is important to maintain adequate monitoring and control of water quality in water treatment facilities that use chloramines for disinfection.

How to chlorinate water?

The chlorine generator CHLORINSITU

At Carbotecnia we have an on-site chlorine generator, a system that uses electrolysis to produce sodium hypochlorite (chlorine) from salt. The chlorine generated can be used for the treatment and chlorination of process water for drinking water, swimming pool water and process water in industry.

To use the CHLORINSITU generator, salt is added to a tank containing the water. An electric current is then applied to the tank, which splits the salt and water molecules to create hypochlorite ions. These ions react with water molecules to form hypochlorous acid, which is the active form of chlorine. The chlorine produced can be used for water treatment.

One of the advantages of using the CHLORINSITU generator is that it eliminates the need to purchase and handle bulk chlorine, which can be dangerous and difficult to transport. In addition, because the machine generates chlorine on site, users can be assured of a constant supply without worrying about availability or transportation.

Another option is the installation of metering pumps that work by controlled dosing of the necessary chemicals into the water, either to add chlorine as a disinfectant or to adjust the pH of the water. Through precise metering systems, metering pumps ensure that the correct amounts of chemicals are mixed with the water in a controlled and safe manner.

Metering pumps for chlorine and other chemicals

Chlorine dosing with pumps is very accurate; and automatically doses liquid chlorine through a controller or can be operated continuously according to the specific needs of water treatment. This allows constant control of the chlorination process and pH adjustment, ensuring reliable and consistent water quality.

It is important to follow the manufacturer’s instructions and recommendations for the correct operation and maintenance of the dosing pumps, in order to guarantee their durability and effectiveness in water treatment.

Disinfection alternatives

Chlorine dioxide (ClO2) has emerged as a promising alternative to traditional chlorine in the water disinfection process in various industrial and treatment applications. Although both substances share similarities in their disinfectant function, chlorine dioxide offers specific advantages that make it attractive in certain contexts.

Some of the benefits of using chlorine dioxide are the lower production of undesirable by-products such as chlorophenols that generate strong odors during chlorination. It also does not generate chlorinated hydrocarbons, which translates into greater safety during the disinfection process.

It is also worth mentioning that chlorine dioxide is effective over a wide range of pH values, so it can disinfect in waters with high variations in acidity.

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On-site chlorine dioxide generator

Bello Zon’s on-site chlorine dioxide generator for water disinfection is a specialized equipment used to disinfect water by means of the on-site production of chlorine dioxide. This generator uses a solution of csodium lorite and hydrochloric acid to produce chlorine dioxide in a safe and controlled manner.

The on-site chlorine dioxide manufacturing process involves the preparation of a chlorine-free solution from the controlled mixture of sodium chlorite and hydrochloric acid. The resulting chlorine dioxide solution is stored in an external reservoir module at concentrations of 1000 or 2000 mg/l, allowing stable storage and constant availability of chlorine dioxide.

This on-site chlorine dioxide generator is widely used in various applications, such as disinfection in the food and beverage industry, water purification, eradication and prevention of Legionella in hospitals, hotels and homes, disinfection of irrigation water in gardening, treatment of cooling and drinking water, disinfection of filters in swimming pools and treatment of public wastewater.

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