Chlorine, Chloramine and Chlorination By-products in Drinking Water

Chlorination, or the process of adding chlorine to water as a way of water purification, is the most widely accepted water disinfection process. This is largely due to chlorine’s high cost-effectivity when used in preventing outbreaks of the world’s most common waterborne diseases. 

However, ever since scientists discovered possibly carcinogenic drinking water contaminants in the form of chlorination by-products, the challenge of purifying water for human consumption has become more difficult. Water suppliers are now forced to adopt more innovative methods of water purification to ensure the safety of their consumers.

Chlorine and its water disinfection capabilities

Compared to other chemical-based water disinfectants like bromine, iodine, chlorine dioxide, and chloramine, chlorine requires the least amount of concentration and contact time in order to inactivate a specified percentage of microorganisms. Some of these organisms, such as E. coli, Polio virus 1, Rotavirus, Norovirus are capable of inflicting severe damage on the human body and can cause widespread contamination.

The rotavirus and noravirus, for instance, are the leading carriers of gastroenteritis. More than 90% of epidemic-grade non-bacterial outbreaks of gastroenteritis worldwide are caused by these two viruses. Why do governments work hard to control these viruses? Because gastroenteritis usually result in diarrhea, which is responsible for up to 2.2 million deaths on the planet every year. It is also the 2nd leading cause of death in children under 5 years of age.

Polio virus 1, on the other hand, is the most common of the three types of viruses that cause polio, a potentially crippling disease that can lead to paralysis and even death.

Chlorine’s ability to destroy these microorganisms more effectively as well as its lower installation and maintenance costs compared to other disinfectants has made it the most favored disinfectant for public water systems.

But despite its exemplary disinfection qualities, chlorination also comes with some serious drawbacks. The most alarming of which is its notoriety for producing harmful chlorination by-products.

Chlorination by-products - why your purified water may not yet be safe to drink

When chlorine is added to water, the purpose is to kill disease-causing microorganisms. However, chlorine may also react with certain substances that may also be present in the water. Sad to say, the resulting chlorination by-products also have harmful effects on the human body. The affected areas are mostly the kidney, liver, heart, and the central nervous system. Some of these by-products can cause reproductive and developmental health risks or even cancer.

The US government is most concerned with two groups of these by-products and has enforced rules to regulate the concentration of these chemicals in drinking water. These groups are the trihalomethanes (THM) and haloacetic acids (HAA5). To mitigate risks associated with these byproducts, annual average concentration limits are specified in the EPA (US Environmental Protectino Agency) Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBP rule).

The regulated chemicals that belong to the group of trihalomethanes are collectively known as total trihalomethanes (TTHM), and are composed of chloroform, bromodichloromethane, dibromochloromethane, and bromoform. The annual average limit set by the EPA for TTHM is 80 parts per billion (ppb).

On the other hand, the five haloacetic acids (HAA5), which are namely, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid, are given an annual average limit of 60 ppm.

For as long as chlorine and the organic or inorganic matter that react with it are present in water, the byproducts will form. Hence, to bring down the health risks caused by these chlorination by-products, you should, at some point in your water purification system, filter out chlorine, the reactive organic and inorganic matter, or the by-products themselves.

Can chloramine replace chlorine?

Chloramine is one of those water disinfectants which are now being used as an alternative to chlorine. One reason for this is that chloramine is less reactive compared to chlorine and hence produces much fewer by-products. Another reason is that it is more stable and hence can last much longer in the water. As a result, it is more effective in preventing bacterial regrowth, which can happen in large water distribution systems.

However, because it is generally a weaker disinfectant compared to chlorine, chloramine is mostly used only as a secondary disinfectant. That is, a water system can have one disinfectant, say UV, to provide the initial disinfection in the treatment facility, and then chloramine is thrown in to provide continuous protection in the distribution system. 

Contrary to popular belief, chloramine still raises some significant health risks. Too much chloramine can cause irritation in the eyes and nose. It can also result in stomach discomfort and anemia. And although the concentrations are much lower than those formed by chlorine reactions, chloramines do form by-products and most of these are not yet well studied.


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