Bleach Sodium Hypochlorite; advantages and disadvantages in the water industry

Sodium hypochlorite is a chemical compound with the formula NaClO. It is composed of a sodium cation (Na+) and a hypochlorite anion (ClO−);



When dissolved in water sodium hypochlorite is commonly known as bleach or liquid bleach.  

It is frequently used as a disinfectant or a bleaching agent. The mixture of sodium peroxide (Na2O2) and hydrochloric acid, which react to produce sodium hypochlorite. is also termed as oxone.

Sodium Hypochlorite; advantages

Disinfection with sodium hypochlorite has similar disinfectant efficiency and residual performance as chlorine gas, but reduces the hazards associated with the handling and storing of chlorine gas especially if generated on-site. With on-site production, NaOCl solutions are less concentrated and less hazardous (typically a 1% concentration) than the standard supplied solution (14% concentration).

As with chlorine gas, it is relatively cheap and can economically disinfect small to large amounts of water. If kept sealed, shelf life is not a factor. It can be easily stored for 1-2 months.

Sodium Hypochlorite; disadvantages

Although safer to handle than chlorine gas, NaOCl is still a hazardous and corrosive substance.

At the standard supplied concentration (14%), storage and handling of NaOCl requires process safety procedures and containment. This is to avoid exposure to workers and the environment and to prevent loss of potency through exposure to air, which causes it to deteriorate. As its disinfection mechanism is essentially the same as that of chlorine gas, NaOCl generally offers no advantage over chlorine gas with regard to disinfection capability and disinfection by-product formation.

In on-site generation, salt is dissolved with softened water to form a concentrated brine solution that is subsequently diluted and passed through an electrolytic cell to form sodium hypochlorite. On-site generation  of sodium hypochlorite produces hydrogen, which presents a fire or explosion hazard if not properly vented

Source: Disinfection Technologies for Potable Water and Wastewater Treatment:

Prepared by: Leslie Snowden-Swan, John Piatt, Ann Lesperance - Pacific Northwest National Laboratory

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