Page 75 - March 2020 - WT Site

Corona Discharge: • Oxidation of Cyanide.

An electrical discharge (a spark) splits an oxygen molecule into Why ozone?
two oxygen atoms. (Electrical discharge is also referred to as
corona discharge.) These unstable oxygen atoms combine with Limitations of Chlorine and UV:
other oxygen molecules. This combination forms ozone. Corona Chlorine:
discharge, also known as silent electrical discharge, consists
of passing an oxygen-containing gas through two electrodes • Chlorine is used to control microbiological load in raw water.
separated by a dielectric and a discharge gap. Voltage is applied
to the electrodes, causing an electron flow through across the • Some strains of bacteria are resistant to chlorine such as
discharge gap. These electrons provide the energy to disassociate pseudomonas and cyst.
the oxygen molecules, leading to the formation of ozone. • Chlorine produces disinfection bi products such as tri

halomethanes, chloro amines and chloroforms which are
Functions of ozone
harmful and continue to remain in water after passing
Disinfection : through carbon and RO.

• Inactivation of bacteria, viruses and fungus by ozone is • Chlorine does not remove taste and odour from water but in
simply oxidation. facts add a foul taste.

• Ozone oxidizes the complex cell wall of these microbial • Does not remove heavy metals from water.
entities and changes the cell structure.
• Does not reduce chemical oxygen demand (caused by
Colour Removal: contamination of waste water in ground water source).

• Ozone oxidizes organic colours. UV:
• The colour causing substances are broken down to simple • UV doesn’t give residual protection. That means the water
organic compounds. can get recontaminated once it leaves the UV tube.
Odour Removal: • UV is ineffective on many living organisms such as amoeba.

• If the odour causing substances are organic in nature, then • UV efficiency reduces with time.
Ozone reacts with them and oxidizes the organics.
Advantages of ozone
• The reaction is almost instantaneous.
• Ozone kills all the living organisms almost instantly.
COD/BOD reduction: • Ozone provides a residual protection in the water.

• Ozone oxidizes COD and BOD. • It improves the taste and the clarity of the water.

• Ozone is used to convert COD to BOD so that bacteria can • It doesn’t form any harmful by products.
digest this BOD.
• Ozone is used to polish the water by oxidizing the tough • It is generated at the site and hence doesn’t require any
COD after biological treatment. operator or chemical storage.
Oxidation of Inorganic Compounds: Case Study

• Ozone oxidizes these heavy metals such as iron & manganese Following Case Study was conducted to check the feasibility
from metallic oxides or hydroxides, which precipitate off and of project: Dhayafule Spinning Mills Pvt. Ltd. in Tandulwadi
can be removed from the water. Madha, Solapur, currently uses the same system to treat and reuse
sewage. Here, we are giving cost comparison of treating water

Water Today - The Magazine l March 2020 77