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Chlorination
Oxidizing Filters
Ozone
Venturi
Aeration

Oxidation to Treat Water

Strong oxidants chemically transform contaminants  to more benign forms and can kill bacteria and viruses.

In order of strength these are potent oxidizers:

  • Hydroxyl Radical (OH0)
  • Ozone (O3)
  • Hydrogen Peroxide (H2O2)
  • Chlorine (OCl) chlorine gas; Sodium Hypochlorite (NaOCl) bleach; there are several other forms of chlorine 
  • Air (Oxygen) O2

The Science

Oxidation within water is the  loss of electrons from the item being oxidized (reducing agent) to oxygen.   Oxidation reduces the number of electrons orbiting an element causing the element to bond with oxygen, which has an attraction for those electrons. Since electrons carry negative charges, oxidation results in an increase of positive valence.

Oxidation

Oxidation within water is the  loss of electrons from the item being oxidized (reducing agent) to oxygen.   Oxidation reduces the number of electrons orbiting an element causing the element to bond with oxygen, which has an attraction for those electrons. Since electrons carry negative charges, oxidation results in an increase of positive valence.

An ionic bond is formed when electrons are transferred from one atom to the other. 

A covalent bond is formed when electrons are shared between atoms. Often, covalent bonds form with a partial transfer (unequal sharing of electrons), resulting in a polar covalent bond.

Iron is most commonly found in its soluble state as ferrous bicarbonate, Fe (HCO3)2.  Ferrous iron has a positive two valence. As ferrous iron is oxidized, the number of electrons is reduced and the iron develops a valence of positive three, ferric hydroxide, Fe(OH)3.

Fe(HCO3)2        + 1/2 O2     + H2O  -> Fe(OH)3            + 4CO2 
Ferrous Bicarbonate Oxygen Water Ferric Hydroxide Carbon Dioxide

Oxygen changes iron to the ferric state which reacts with alkalinity in the water and forms an insoluble brown ferric hydroxide precipitate. The dissolution of the carbon dioxide in water also forms carbonic acid. The presence of carbonic acid lowers the pH, and in low alkalinity water (2-3 gpg total solids), this may cause corrosion problems within the system.

Bleach, Sodium Hypochlorite (NaOCl) is a clear slightly yellow liquid solution and has an available chlorine content of approx. 5.25 percent. 

When the highly alkaline bleach is added to water the alkalinity is reduced, releasing the chlorine. The chemical equation of adding NaOCl to water is:

NaOCl       + H2O     -> HOCl               + NaOH
Sodium Hypochlorite Water Hypochlorous Acid Sodium Hydroxide

The potent bactericide is the Hypochlorous Acid (HOCl).  The chlorine in hypochlorous acid is an active oxidizing agent combining readily with other substances.  As hypochlorous acid combines with substances it is used up. The amount of chlorine required to maintain the target residual is called chlorine demand.

As this acid ionizes as HOCl  --> H+   + OCl- its efficiency is decreased.  pH strongly affects the degree of ionization.  

pH Hypochlorous Acid (HOCl) Hypochlorite Ion (OCl-)
(active oxidizing agent) (Inactive agent)
7.0 78 % 22%
7.5 50% 50%
8.0 21% 79%
9.0 1% 99%

Manganese

The simplified reaction of manganese oxidation is as follows:

2Mn        +   O2     + 2H2O  ->     2MnO2          + 4H 
Manganese Ion Oxygen Water Manganese Dioxide Hydrogen Ions

The resultant Manganese Dioxide is a black insoluble material. The hydrogen ions will  cause the water to become more alkaline.  

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Last modified: November 13, 2018