Ozone occurs readily in nature, especially during thunderstorms.  The high voltage of lightning converts oxygen to ozone.  It is possible to smell ozone as the fresh and clean odour after such a storm.  The most familiar ozone is the ozone layer above the earth’s atmosphere where ozone is created by the sun’s ultra violet rays to protect us from ultra violet.

Physical properties
Ozone is a pale-blue poisonous gas (like chlorine) with a sharp, irritating odour.  People can smell a concentration of 0.01 ppm.  Exposure to 1 ppm can cause headaches, burning eyes, and irritation to the respiratory passages.

How does ozone work?
The third oxygen atom makes ozone extremely reactive.  This atom readily oxidizes contaminants such as odours, moulds, protozoa, bacteria and viruses.  Ozone works according to the principle of oxidation.  When the ozone molecule (O₃) comes into contact with something “oxidationable”, the charge of the ozone molecule will directly flow over, and oxidize the other material, eg. a cell wall of a micro-organism by creating tiny holes in the wall.  The cell wall collapses and the ozone penetrates the organism and destroys (oxidizes) the enzymes, protein, DNA and RNA within the cell.  This process is called lyses.  The cells die within a few seconds.

We often find micro-organisms in water which may be harmful to humans and animals.  Both ozone and chlorine can kill pathogens, but ozone is significantly more effective in killing viruses and cyst-forming organisms, particularly chlorine resistant organisms, such as Cryptosporidium.
 

How ozone kills organisms

Oxygen molecules are released and oxidizes the membrane and DNA

How is ozone manufactured?
In nature ozone is produced in two ways:

• Lightning: Oxygen near the ground creates ozone in the presence of lightning flash (corona discharge).
• Ultra violet:  Oxygen from the atmosphere creates ozone in the presence of the sun’s ultra violet rays.

The most popular method of ozone production for industries and personal use is by using a corona discharge generator.  Oxygen is forced between high voltage plates to simulate a corona discharge.  The diatomic (O₂) oxygen is broken up and form triatomic (O₃) oxygen which is ozone.

Advantages of Corona Discharge

• It produces high ozone concentration
• It works best for water applications
• Removes organic odours fast
• Equipment can last for years without any maintenance

What is the half-life of ozone?
For the purification of water and air ozone must be produced on-site.  Because of its short half-life, ozone will decay soon when produced.  The half-life of ozone in water is about 30 minutes.  This means that ozone will decay back to oxygen within 30 minutes.

How safe is ozone?
In high concentrations ozone is poisonous to humans and animals.  It needs to be handled with care like any oxidizing agent.  An ozone concentration of 0,4 mg/L is safe for human consumption.  A concentration of 0.7 mg/L can be used to sterilize water bottles.

Certain chain stores use ozone to disinfect their vegetables and fruit.  Ozone destroys bacteria and moulds which start the decaying process and prolongs their shelf-life.

Only a few materials, such as stainless steel (grade 316), glass, polytetrafluorethylene, or polyvinylidene fluoride may be used with ozone due to its high oxidation potential.

Sources
www.wikipedia
www.lentech
www.watertechonline
www.wqa.org
www.gewater
www.ozonerp
www.keeginternational