Question

What is the purpose of adding carbon dioxide gas (CO 2 ) in treating water for public supply?
Give pertinent chemical reaction equations.

Answer 1

Desalinated water has poor mineral content, which makes it unpalatable and corrosive. So to get rid of these situations, remineralization is essential. Commonly used remineralization proocess is allowing desalinated water through lime beds, which induces CO2 dosage into water and reintroducing bicarbonate alkalinity and calcium hardeness to water.

In lime softening plant CO2 is mainly used for two purposes:

1. For pH adjustment

2. For precipitation and neutralization of calcium hydroxide in the primary effluent basin where high magnesium waters are softened by excessive lime treatment follows by recarbonation.

There are several advantages of using CO2 for this purpose:

1. Carbon dioxide reduces pH levels in water very quickly.

2. It is non corrosive to pipes and equipment.

3. Requires less operation and maintenance cost.