Breakpoint Chlorination

Definition - What does Breakpoint Chlorination mean?

Breakpoint chlorination is the point where the demand for chlorine has been fully satisfied in terms of chlorine addition to water.

When chlorine is added to water, a reaction is produced in the compounds present in the water. These compounds utilize the chlorine, resulting in zero chlorine residual.

Corrosionpedia explains Breakpoint Chlorination

Once chlorine has been added to water, it is consumed by a type of chemical reaction that has a net effect of increased concentration of chlorine. For typical addition of chlorine, the rate of reaction instantly speeds up, reducing the concentration of chlorine. This is because chlorinated compounds acquire more chlorine.
The pace at which the chlorine atom is added is comparatively slow, but the rates can be faster for the following reactions since chlorinating potentiates an activity called reactivity. Once almost all of the chlorine reactions are accomplished, adding more chlorine leads to permanent residual.
The period wherein the concentration of chlorine goes into an upward slope is called the "breakpoint." In some cases, there can be no breakpoint seen because various organic compounds react at different rates.

Breakpoint chlorination is usually measured to determine when chlorination has been satisfied. This is a common practice in disinfecting water in industrial water systems as well as swimming pools. It is one of the most typical forms of chlorination where adequate chlorine is incorporated into the water to achieve the breakpoint, keeping the water well chlorinated and appropriate for its intended use.

Chlorine Demand

Definition - What does Chlorine Demand mean?

Chlorine demand is the difference between total chlorine added in the water and residual chlorine. It is the amount which reacts with the substances in water, leaving behind an inactive form of chlorine. Chlorine demand can be caused in a water body due to rain containing ammonia or the addition of fertilizers which can be oxidized by chlorine.

Corrosionpedia explains Chlorine Demand

To purify water supplies and make them suitable for purposes like drinking, cooking and swimming, chlorine is added. Chlorine demand from the total chlorine added can be explained using the following equation:

Chlorine demand = Total chlorine – Chlorine residual

The purity of water can be determined by monitoring the value of chlorine demand. If the value is zero, the water is already free of pathogenic microorganisms. If the value is less than the total chlorine, it shows that the amount of chlorine added initially to the water was sufficient.

Residual Chlorine

Definition - What does Residual Chlorine mean?

Residual chlorine is the amount of chlorine that remains in the water after a certain period or contact time.
Testing for residual chlorine is one of the most common tests used by water treatment plants. Through the residual chlorine test, the remaining chlorine amount is determined in water that has finished testing and is ready to be released in the distribution system.

Corrosionpedia explains Residual Chlorine

There are three forms of residual chlorine in water treatment:

• Free - Residual chlorine composed of dissolved hypochlorite ions, hypochlorous acid and chlorine gas
• Combined - Composed of chloramines that can kill bacteria and oxidize organic matter
• Total - The sum of free and combined residual chlorine

Hypochlorous acid and other strong acids are used as oxidizing agents for disinfecting drinking water. However, these acids can also react as oxidants, especially with lead, which increases the chances of lead corrosion. Therefore, operators in water treatment and distribution plants must ensure that there is the proper amount of residual chlorine as the water reaches the end of the system.
In different settings and situations, there are sometimes required residual chlorine levels to prevent the occurrence of corrosion in water. This level must be determined and carefully studied by water plants for safe and efficient water processing and distribution.

Free Available Chlorine

Definition - What does Free Available Chlorine mean?

Free available chlorine is the part of the total chlorine measurement that has not yet reacted with contaminants. Therefore, it is called available or free.
The total chlorine in this case is the sum of combined available chlorine and free available chlorine, also called total residual chlorine.

Corrosionpedia explains Free Available Chlorine

Chlorine is usually added to water in different forms such as:

• Chlorine gas
• Sodium hypochlorite or liquid bleach
• Lithium hypochlorite
• Stabilizers

When any of these chlorine forms are added to water, a highly potent bactericide known as hypochlorous acid is created. This is a type of weak acid that can be dissociated into hypochlorite ions.
Hypochlorous acid and hypochlorite ions, when combined, is known as free chlorine. Both of these establish equilibrium and are both temperature and pH dependent at 7.5 pH and 77°F (25°C). Hypochlorous acid is more potent than hypochlorite ions in terms of disinfection. Through proper control of pH, hypochlorous acid remains dominant in the solution of free available chlorine to ensure its effectiveness as a bactericide.

Free available chlorine readily reacts with compounds such as ammonia to produce chloramines, or industrially known as combined chlorine. Although chloramines also have antibacterial properties, these are about 80 times less effective than free chlorine.
In the formation of free chlorine and chloramines, optimum temperature, pH as well as mixing conditions should be taken into consideration.

Feedwater Treatment

Definition - What does Feedwater Treatment mean?

Feedwater treatment is a pre-water treatment process to control deposition, eradicate impurities and prevent corrosion within a boiler system. In a boiler system, water is transformed into steam and expands by as much as 1000 times as it passes through steam pipes at rates of 100km/hr.
Steam is necessary to move heat and energy from central boilers to its desired location. Without proper feedwater treatment, a plant or facility that produces steam undergoes corrosion and scale formation.

Corrosionpedia explains Feedwater Treatment

Corrosion is one of the most serious problems within steam systems that consume high volumes of water. Fresh water has high amounts of dissolved oxygen. When this oxygen is mixed with elevated temperatures, it becomes highly corrosive, particularly for the steel piping in boiler systems that are made of carbon.
In order to prevent corrosion, oxygen that is present in the pure water to be used in the production of saturated steam must be eliminated through the use of chemicals and de-aeration towers. This is what feedwater treatment does. The most common chemicals that act as scavengers during the process include sodium erythorbate, sodium sulfite and hydrazine.
When a boiler is not treated, it can turn into a potential bomb, and the steam can cause scalding and serious burns in addition to damining equipment and/or the facility. Corrosion damage and scale formation could also result in reduced efficiency, low steam quality, unreliable operations and shorter lifespan of the involved facility.