Chloramines

Drinking water odor and flavor have improved by the application of chloramines from the beginning of the twenty-first century. Eventually chloramines were also used for disinfection.

What are the properties of chloramines?

Chloramines are formed during a reaction between chlorine (Cl₂) and ammonia (NH₃). Chloramines are amines which contain at least one chlorine atom, which is directly bond to nitrogen atoms (N). Inorganic chloramines are formed when dissolved chlorine and ammonia react. During this reaction three different inorganic chloramines are formed; monochloramine (NH₂Cl), dichloramine (NHCl₂) en trichloramine (NCl₃).

Inorganic chloramines, free chlorine and organic chloramines are chemically related and can change into one another easily. These compounds cannot be found in isolated form. Inorganic chloramines are not persistent; however, these compounds are more persistent than freely available chlorine compounds. Research has shown that the half-lives of inorganic chloramines can vary from one minute to 23 days, depending on the circumstances.

How are chloramines produced?

Chloramines are frequently produced by adding ammonia to water containing free chlorine (HOCl or OCl, depending on the pH). The ideal pH value for this reaction is 8.4. This means the water is slightly alkaline.

Reaction mechanism:

NH₃ (aq) + HOCI NH₂Cl + H₂O

When the reaction takes place three kinds of inorganic chloramines can be formed. The pH value determines which kind of chloramines is formed. Trichloramines mainly form when the pH value is 3 or below. When the pH value is 7 or above, dichloramine concentrations are highest.
The amounts of chlorine and ammonia in the water also influence the origination of chloramines. The chlorine/ ammonia rate is ideally 6:1. During chloramine production the rate is usually 3-5:1. When ammonia concentrations are higher, more di- and trichloramines are formed.

Organic chloramines can also be formed during these reactions. Organic chloramines cannot be distinguished from other chloramines, using standard chloramine analysis methods.

Figure 1: pH values determine which kind of chloramine is formed

Table 1: various types of chloramines and their properties

appearance	name	molecular weight	preferred pH value	biocidating effect
NH2Cl	monochloramine	52	> 7	good
NHCl2	dichloramine	85	4 - 7	tolerable
NCl3	trichloramine	119	1 - 3	average
RNHCl	organic chloramines	varies	unknown	bad

What are the applications of chloramines?

Chloramines can be used as bleach, disinfectants and oxidators. Organic disinfectants slowly give off chlorine, causing a slower and less aggressive disinfection than with hypochlorite (OCl^-). Chloramines can be used to improve odor and flavor of the water when chlorine is used as a disinfectant. Chloramines are also used for the disinfection of drinking water and wastewater and to resist biofouling in cooling water systems.

Water disinfection with chloramines

When chloramines are used as a disinfectant, ammonia is added to chlorine treated water. Ammonia is added after chlorine, because this causes CT values to be lower than when ammonia is added primarily.

Chloramines are as effective as chlorine for the deactivation of bacteria and other microorganisms, however the reaction mechanism is slower. Chloramines, like chlorine, are oxidators. Chloramines can kill bacteria by penetration of the cell wall and blockage of the metabolism. Monochloramine is the most effective disinfectant. It reacts directly with amino acids in the bacterial DNA. During deactivation of microorganisms chloramines destroy the shell which protects a virus. When the pH value is 7 or higher, monochloramine is the most abundant chloramine. The pH value does not interfere with the effectiveness of chloramines.

Is drinking water disinfected using chloramines?

Chloramines are applied more and more often in the United States as an alternative for chlorine during secondary disinfection of drinking water. In the year 2002, 20% of the US drinking water production companies used chloramines. The main reason for the transfer from chlorine to chloramines is that chloramines react with organic matter less often than chlorine. Little to no trihalomethanes (THM) and other disinfection byproducts are formed during chlormaine disinfection.

Chloramines will remain actively within the plumbing much longer. This is because it takes long for chloramines to be broken down. Chloramines do not give off any taste or smell and are relatively safe.

Can chloramines be removed from water?

Chloramines remain active in the water system for a considerably long period of time. Like other molecules, chloramines contribute to the total amount of dissolved solids in the water. Like chlorine, chloramines are selectively reactive and may have damaging affects when they remain in the water for too long.

When chloramines are present, there are usually trace amounts of ammonia and hypochlorite in the water as well. Chloramines are hardly ionic. As a result and because of the low molecular weight, chloramines, mainly monochloramine, are difficult to remove from water by reverse osmosis (RO) or water softening. Boiling and distillation cannot be used either. Substances for chlorine removal cannot be used for the removal of chloramines. Sunlight and aeration may aid chloramine removal.

Chloramines can be removed by means of a granular active carbon filter. This filter brings down chloramine concentrations from 1-2 ppm to less than 0,1 ppm. One must make sure that the active carbon comes in contact with chloramines for a significant amount of time. An active carbon filter is a selective, which means it also removes other compounds, such as chlorine (reduction to chloride), hydrogen sulphide, organic compounds, THM, pesticides and radon. When these compounds are present in water, this will influence the capacity of the filter.

The amount of chloramines in the water can be determined by measuring the 'total chlorine' residu. This means measuring the 'total amount of chlorine' or the 'amount of chlorine compounds'.

What benefits and drawbacks are there to using chloramines?

What are the benefits?

Few disinfection byproducts

Using chloramines benefits over using chlorine, because few organic compounds (trihalomethanes; THM) and other possibly carcinogenic byproducts (halogenic acetic acid; HAA) are formed.

Chloramines remain active for a long time

Chloramines remain in the water longer than chlorine. Monochloramines are most effective when the pH value is 7 or higher. When the pH value exceeds 7 the water is alkaline. The benefit of alkaline water is that it is less corrosive than acid water. When the pH value is high chlorine can be found in the water as hypochlorite ions (OCl^-). These ions have a higher oxidation potential than underchloric acid. However, as a disinfectant it is a hundred times less effective than underchloric acid. When pH values are too high, its affectivity will diminish.

Chloramines increase taste and smell of the water

Chloramines do not alter the pH of the water. Chloramines provide a better taste and smell than chlorine. Chloramines are often applied to prevent a chlorine taste or smell.

Chloramine disinfection can be improved by raising temperatures.

What are the drawbacks?

Are organic chloramines formed?

When large amounts of organic matter are present in the water, organic nitrogen causes the formation of organic chloramines. These do not possess the same disinfection properties as inorganic chloramines. This situation occurs when organic matter contents exceed the 3 ppm boundary.

What is the reaction rate of chloramines?

The drawback of chloramines is that they are less reactive than chlorine. Part of the disinfectant remains in the water, where it will be consumed by bacteria or broken down. This process can take weeks. Contrary to chlorine, chloramines do not perish when the water lies still for a few days. As a result chloramines need to be removed from water. Chloramines can be removed by using granular active carbon or acetic acid.

What is the effectivity of chloramines?

In Massachusetts, research has been carried out to bring to light the death causes of people that used water disinfected by chlorine or chloramines. The results show that the number of people dying from bladder cancer was higher when the water was chlorinated. When water was disinfected by chloramines, people were more likely to die from pneumonia or flues. This may show that chloramines are less effective than chlorine for the elimination of pathogenic microorganisms.

Do chloramines form nitrates?

High amounts of ammonia serve as nutrients for nitrifying bacteria in the water, which can cause nitrate levels in the water to rise. Nitrate is converted to nitrite in the stomach. Nitrites can react to N-nitrosamines with proteins in fish. These compounds may be carcinogenic. Young children are more susceptive to nitrites. When children are below 0,5 years old they cannot drink nitrate-rich water, because nitrites cause the oxygen level in the blood to fall (Blue Baby Syndrome). It is advised to feed baby’s with water that has a nitrate content of below 25 μg/L.

Can ammonia cause corrosion?

When chloramines are chemically removed, ammonia may be released. The toxic effect that ammonia has on fish can be prevented by the application of biological filters, natural zeolites and pH-control.

Ammonia causes corrosion of lead and copper. Nowadays most waterworks are made of lead or copper. In Washington DC (US), increased lead concentrations in drinking water caused by chloramine disinfection caused a fuss in 2003. However, drinking water companies do not plan to switch back to using chlorine, because this can no longer comply with the standard for disinfection byproducts, which was lowered to 80 μg/L by the EPA. Chloramines are used because of a lower concentration of disinfection byproducts. To prevent corrosion, orthophosphates are added.

What are the health effects of chloramines?

Water that is disinfected by chloramines does not cause a health threat. It can be used for drinking, bathing and washing and is suitable for several daily domestic purposes.

What are the dangers to kidney dialysis patients, fishes and amphibians?

Drinking chloramine-containing water or using it for boiling and bathing is safe, because of a neutralization of chloramines in the metabolism. However, people with weakened immune systems, such as young children, elderly people, people with HIV and people that undergo chemo therapy, should also be cautious when it comes to the use of chloramine disinfected water.

Kidney dialysis patients and people that own fish, reptiles or amphibians should be careful. With kidney dialysis patients the blood comes in contact with water in a semi permeable membrane. This can cause chloramines to directly enter the blood vessels. Chloramines are toxic to the blood.
Fishes can directly take up chloramines in the blood through their gills. Chloramines are toxic to fishes, too. Water that is used in aquaria should be free from chloramines.

What is the legislation for chloramine disinfection?

According to American guidelines by EPA, drinking water that is treated with chloramines can contain a maximum amount of 4 mg/L Cl₂. (National Primary Drinking Water Regulations EPA, 2002)