In the fight against the recent coronavirus pandemic, chlorine bleach has emerged as a true winner due to recommendations from the Centers for Disease Control (CDC), the Environmental Protection Agency (EPA) and the World Health Organization (WHO).
This powerful chlorine compound has a proven track record to safely remove both bacteria and viruses from surfaces and from the water. The CDC has stated “there is no evidence that Covid-19 can spread to people through the water used in pools, hot tubs or water playgrounds. Proper operation and disinfection of pools, hot tubs and water playgrounds should kill the virus that causes Covid-19.”
In the pool industry, liquid chlorine, or sodium hypochlorite, has long been recognized as one of the most effective tools for achieving clear and sparkling algae free water. In more recent years, alternative sanitizers have been developed for those opposed to chemical use. But with the reality of Covid-19, the simplicity and relative cheapness of bleach use has caused it to fly off the shelves.
Bleach, or sodium hypochlorite, has the great benefit of being able to both sanitize and disinfect, which may sound like the same thing, but the two words have slightly different definitions.
According to theAmerican Chemistry Council- “‘Sanitizing’lowers the number of germs on a surface or object by reducing the germs to levels considered safe by public health standards or requirements. ‘Disinfecting’ however, kills germs by using antimicrobials directly on surfaces and objects”.
When added to water, sodium hypochlorite forms a powerful antimicrobial molecule called hypochlorous acid.
NaOCl + H2O → NaOH + HOCl
Hypochlorous acid is effective at inactivating up to 99.9% of bacteria in water. At the proper dilution, it also works to disinfect surfaces to remove microbes.
Making Sodium Hypochlorite
Sodium hypochlorite or liquid bleach, was developed in 1785 by frenchman Claude Louis Berthollet. His original method involved passing chlorine gas (Cl2) through a sodium carbonate solution, but the resulting solution of sodium hypochlorite was weak.
Hasa, Inc., a leading producer and distributor of high quality water treatment solutions, makes use of the chlor alkali process to manufacture their sodium hypochlorite. This process uses table salt, or sodium chloride as a basis for the sanitizer.
Specifically, water is added to salt to make brine, which is then filtered for purity. In a cell room, electricity is applied to the brine to break it up into sodium hydroxide (NaOH) chlorine (Cl2) and hydrogen gas. This is then sent to Hasa’s plants by rail car and tanker trucks.
At the plants, chlorine is mixed with sodium hydroxide, resulting in sodium hypochlorite, salt and water. These plants operate under tight controls to produce varying strengths of sodium hypochlorite.
The overall chemical reaction is:
Cl2 + 2NaOH → NaOCl + NaCl + H2O + heat
or, chlorine + sodium hydroxide (caustic soda) → sodium hypochlorite + sodium chloride + water + heat.
One of the differences in the way Hasa produces sodium hypochlorite is in the high-pressure filtration process. Because the raw materials are earth mined, they contain certain metal impurities. Hasa uses a triple filtration system to remove some of these impurities, such as copper, iron, nickel and metal. These impurities are part of what causes sodium hypochlorite to lose its strength.
Sodium hypochlorite is unstable and has a limited shelf life, meaning that the chemical will decompose and the available chlorine will decrease over time.
Time, temperature, pH and exposure to light are some of the major factors that also affect its stability.
The Chlorine Institute developed a formula for estimating the concentration of sodium hypochlorite stored at a temperature of 80°F at a starting concentration of 13% (see table).
After 45 days, for example, 13% sodium hypochlorite will decompose to just over 10%. For this reason, it is a good idea to purchase only the amount that can be used soon after purchase. Otherwise, the liquid chlorine is less powerful and more will be needed.
Liquid chlorine also decomposes in the presence of UV light, so it should be purchased in vessels that do not transmit light to avoid unnecessary decomposition.
The pH of the liquid chlorine is another factor that affects its stability. For this reason, manufacturers add a slight excess of sodium hydroxide to commercial chlorine. This is the reason pH tends to go up after the addition of liquid chlorine.
Sodium hypochlorite is incompatible with many chemicals, and should not be mixed directly with ANY other chemical.
Within the pool industry, there are specific chemicals that are commonly used that must never be mixed.
Sodium hypochlorite is incompatible with acids. If accidental mixing occurs, it will produce chlorine gas, resulting in toxic fumes. Therefore liquid chlorine should never be mixed with muriatic acid; HCl sulfuric acid; Alum (aluminum sulfate); phosphoric acid; some sequestering agents; and brick or concrete cleaners.
It is also incompatible with chemicals and cleaning compounds that contain ammonia. These may form explosive compounds, and other chlorine gases. Therefore, chlorine should never be mixed with ammonium hydroxide, or quaternary ammonium salts or quats, known as algaecides.
Additionally, liquid chlorine should not be mixed with organic compounds due to the formation of chlorinated organic compounds and potentially chlorine gas. Therefore liquid chlorine should not be mixed with enzymes, insecticides or solvents.
Sodium hypochlorite is incompatible with hydrogen peroxide and will release oxygen gas and may be explosive.
Care must also be taken when using any reducing agents such as sodium thiosulfate, which is commonly used to neutralize chlorine before testing. The heat evolved in a concentrated reaction may cause splashing or boiling.
Finally, avoid direct contact with sunlight, which could cause over pressurization of the container.
Hasa’s Muriatic Acid
Hasa’s ‘Sani-Clor’ Sodium Hypochlorite