Jun 16, 2021

What is Sodium Hypochlorite (SH)?

What is sodium hypochlorite, how is it used and why is it used?

What is sodium hypochlorite? It is a disinfectant used in municipal water applications to kill pathogens.

Sodium hypochlorite (SH) is a household chemical that has been widely used since the 18th century. It’s a chlorine compound and has several industrial uses, including public water treatment

It usually has around 10 to 12% available chlorine, which is the amount of chlorine released for disinfection

This short guide will explain sodium hypochlorite’s ability to disinfect water, how this chemical is produced, any regulations for using it, and its advantages and disadvantages. 

Advertisement

What is SH Used For?

SH is a bleach or disinfectant, and is capable of killing pathogens like bacteria, viruses, fungi and mycobacterium. It can be used as a household cleaner, thanks to its destaining properties, and may also be an ingredient in laundry detergents and deodorizing products. 

Industrial uses of sodium hypochlorite include use in chemical, food and glass factories, as well as in waste disposal and pharmaceutical industries. It can also be used to bleach textiles, and may be used to reduce odors in industrial wastewater. Additionally, it can prevent the growth of algae in cooling towers. 

It’s also very common for SH to be used as a disinfectant in swimming pools. Additionally, this chemical is used around the world in industrial and municipal water treatment applications, making water clean and safe to drink. 

Advertisement

How Does SH Disinfect Water?

Just like chlorine, when sodium hypochlorite is released in water, it produces hypochlorous acid. This acid then reacts with pathogens in the water, like bacteria, viruses and protozoa, and deactivates them, preventing them from being able to reproduce or pose a risk to human health. This reaction process is known as oxidation. 

What Are the Regulations Regarding SH Use?

According to the CDC, the acceptable range of free chlorine in water is 0.5 to 2 parts per million, so it stands to reason that water treatment companies must make sure to monitor water and make sure that it contains less than this amount when using SH as a disinfectant. 

Advertisement

What Are the Health Effects of Sodium Hypochlorite?

There are several potential health effects of sodium hypochlorite, though these effects are highly unlikely to arise from drinking or being exposed to water that has been disinfected with small quantities of the chemical.

However, some of the health risks of exposure to SH-disinfected water include the following.

Higher incidences of certain cancers

Research has found that drinking SH or chlorinated water may be linked to higher incidences of breast, rectal and bladder cancers. It’s thought that SH can react with the organic compounds found in water to create trihalomethanes, which have been found to encourage cancer-forming free radical growth. 

May aggravate skin & hair

Showering in water treated by chlorine or sodium hypochlorite may aggravate your skin and scalp, especially if you have pre-existing skin conditions like eczema. You may experience dryness, itchiness, and hair breakage from frequent exposure to SH water. 

Breathing difficulties

Again, showering in SH water may affect a pre-existing lung condition like asthma, as when you breathe in steam containing SH and its byproducts, they may settle in your airways. 

Burning risk

Inhaling higher levels of SH puts you at risk of coughing, a sore throat, and even a burning sensation. If you swallow large quantities of SH, you may experience digestive issues such as diarrhea, vomiting and stomach ache. 

What Are the Advantages of Sodium Hypochlorite?

Some of the notable advantages of SH are that it:

  • Has a similar disinfectant efficiency as chlorine;
  • Is safer to handle and store than chlorine;
  • Kills the majority of live pathogens in water;
  • Is relatively cheap and can be used to economically disinfect large amounts of water; and
  • Has quite a long shelf-life as it can be stored for up to two months. 
Advertisement

What Are the Disadvantages of Sodium Hypochlorite?

Some of the biggest disadvantages of sodium hypochlorite are that it:

  • Loses potency when in contact with air, so must be stored correctly;
  • Is still a dangerous and corrosive chemical, although not as unsafe as chlorine;
  • Is not capable of deactivating Giardia Lamblia and Cryptosporidium; and
  • May produce harmful byproducts when used as a disinfectant in municipal drinking water.

RELATED: Electrochemical Disinfection Primer

How is Sodium Hypochlorite Produced?

There are two different methods that can be used to produce SH. 

The first is to use an electrolysis system to dissolve salt in softened water, producing a liquid brine. When this solution is electrolyzed, SH is produced. Hydrogen gas, which is highly explosive, is also produced during this reaction, so it is important that safety measures are taken before, during and after producing SH in this manner. This process is fairly slow, but it does not involve chemical storage or transport, which is an advantage. 

Alternatively, it can be produced by adding chlorine in gaseous form to caustic soda. This produces salt and SH.  

About the author

Brian Campbell is the founder of WaterFilterGuru.com, where he blogs about all things water quality. His passion for helping people get access to clean, safe water flows through the expert industry coverage he provides. Follow him on twitter @WF_Guru or contact him by email [email protected]

expand_less