There are two disinfectants associated with chlorine.
- HOCl Hypochlorous Acid, is a very effective disinfectant
- OCl- Hypochlorite Ion, is many times less effective than HOCl 2Cl2 + 2H2O = 2HOCl + 2HCl
Chlorine gas when added to water produces Hypochlorous acid plus Hydrochloric Acid.
The Hypochlorous Acid then partially disassociates to the Hypochlorite Ion (OCl-): 2HOCl = HOCl + H+ + OCl-
The extent of the disassociation depends on the pH of the water (6.5 to 8.5)
2Cl2 + 2H2O = HOCl + H+ + OCl- + 2HCl
The higher amount of HOCl remaining, the greater the disinfection efficiency. (Lower solution pH).
The above is the classical method of disinfection by chlorine. Chlorine was (and is) distributed in upright gas cylinders which is an inexpensive method for disinfection. The major disadvantages are safety in transportation and at the point of use (POU).
Various methods have been tried to avoid the use of gaseous chlorine. The most successful is the manufacture of sodium hypochlorite and calcium hypochlorite. Sodium hypochlorite is the main ingredient in bleach. Calcium hypochlorite is primarily used commercially.
Sodium hypochlorite when added to water produces:
NaOCl + H2O = HOCl + OH- + Na+
Sodium hypochlorite plus water produces hypochlorous acid plus hydroxyl ions plus sodium ions. The objective, as with gaseous chlorine, is to add hypochlorous acid to the water. Similar chemistry applies with calcium hypochlorite.
The disadvantage for both sodium hypochlorite and calcium hypochlorite is the need to transfer dangerous chemicals to the POU. In addition, calcium hypochlorite supports combustion and is a fire hazard.
Envirocleanse is the latest entry for producing hypochlorous acid inexpensively and at the POU. No transport problems, no fire problems, and biodegradable.
Envirocleanse electrolyzes brine to produce hypochlorous acid.
2NaCl + 6H2O + Electricity = 2HOCl + O2 + 4H2 + 2 NaOH
The oxygen and hydrogen gases are vented to atmosphere and the dilute sodium hydroxide is a waste stream. As with gaseous chlorine or sodium hypochlorite, the remaining hypochlorous acid partially disassociates to:
HOCl = H+ + OCl-
The combination of HOCl and OCl- effectively destroy the microorganisms.
HOCL from chlorine gas
- Chlorine gas produces sodium hypochlorite Cl2 + 2NaOH = NaCl +NaClO + H2O
- Sodium hypochlorite produces hypochlorous acid NaOCl + H2O = HOCl + Na+ + OH-
HOCl from ordinary salt
- Envirocleanse Brine plus electricity produces hypochlorous acid directly 2NaCl + 6H2O + Electricity = 2HOCl + O2 + 4H2 + 2NaOH No harsh chemicals