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What is Ozone?

Ozone is 'active oxygen' where each ozone molecule contains three oxygen atoms (tri-atomic) whereas normal oxygen contains only two oxygen molecules. Ozone is a very reactive and unstable gas with a very short life and reverts to oxygen form rapidly. Ozone is a naturally available disinfectant and is a powerful oxidation agent. Ozone is naturally created due to the combination of oxygen in air and the UV rays of the sun. Ozone is used as an alternative water purification technology to UV radiation and chemically-induced (chlorine and bromine) processes. Ozone is often referred as an environment-friendly or the green chemical of the future. Ozone can be produced through electro-mechanical equipments known as ozone generators.

Ozone is naturally present in the atmosphere as a layer which protects the earth from deadly UV radiations emanating from the sun rays. It is produced as a result of the reaction of UV rays of the sun with the earth's upper atmosphere (stratosphere). In stratosphere, small amounts of ozone are constantly being made by the action of sun's UV light on oxygen molecules. Oxygen molecules absorb the UV radiation and split to form single oxygen atoms. These atoms combine with the remaining oxygen (O2) molecules to form Ozone (O3). On the ground level, ozone is formed as a result of lightning strikes during thunderstorms. The life cycle of ozone is i. Generation ii. Oxidation and iii. Revert to oxygen.

Raw Water Treatment Plants - Ozonators

Ozonation Process

Ozone is manufactured by passing an electrical discharge through O2 gas or through dry air. The resulting mixture of ozone and O2 or air is usually suitable for most applications of ozone. Because of its relatively short half-life, ozone is always generated on-site by an ozone generator and injected into the water or air immediately.

The two main methodologies of ozone generation are UV-Light or corona-discharge (CD). Ozone generation by CD is the most common method adopted by manufacturers and is more advantageous. Advantages of CD method are greater sustainability of the unit, higher ozone production and higher cost effectiveness. UV-light method is feasible only where production of small amounts of ozone is required. (eg. laboratories). The CD unit comes with the following parts.

i. Feed source (oxygen / air) , ii. Dust filters, iii. Gas dryers, iv. Ozone generators, v. Contacting units and vi. Torch destruction.

Ambient air (compressor) or pure oxygen (oxygen generator) can be used for the production of oxygen. The air should be conditioned by using air dryers and dust filters. This conditioned air is passed through highly efficient ceramic electrodes in the Ozone Generator where the O2 molecules are broken to form O3. Ozone thus formed is mixed with the water via a venturi injector or a diffuser. Venturi injectors effectively mix ozone in the water. They work by forcing water through a conical body which initiates a pressure differential between the inlet and outlet ports. This creates a vacuum inside the injector body which initiates ozone suction.

Excessive or unused ozone is broken down by using ozone destructors. The methodology of ozone destruction is by applying a suitable catalyst which accelerates the decomposition of ozone into oxygen (e.g. magnesium oxide).

Properties of Ozone

Formula: O 3

Nature: Gaseous and unstable - 1.5 times heavier than oxygen

Smell: Pungent at as low a concentration as 0.03 ppm in air

Colour: Colourless

Melting and Boiling Points: 193.C and 112.C respectively

Solubility in water @ 20.C: 0.381 grams / per litre

Density: 2.14 grams / per litre

Efficacy: 3000 times more powerful than chlorine in disinfection and 50 times more powerful in oxidation.

Durability: Ozone cannot be stored or transported because of its unstable tendency to break down quickly.

Besides these properties, ozone also acts as a micro-flocculant. Oxidation of dissolved organics by ozone results in polar and charged molecules that react with polyvalent aluminium or calcium to form precipitates. This also improves the settling property of the particles. The precipitate can be removed by filtration. This treatment is referred to as pre-ozonation.