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Methods of Treatment for Water Contaminants

Carbon Dioxide

Source of Carbon Dioxide

Free carbon dioxide (C02) exists in varying amounts in most natural water supplies. Most well waters will contain less than 50 ppm. Carbon Dioxide in water yields an acidic condition. Water (H2O) plus carbon dioxide (C02) yields carbonic acid (H2C03). The dissociation of carbonic acid yields hydrogen (H) and bicarbonate alkalinity (HCO3). The pH value will drop as the concentration of carbon dioxide increases, and conversely1will increase as the bicarbonate alkalinity content increases.

H20 + CO2 <===> H2CO3 <==> H+ + HCO3

Water with a pH of 3.5 or below generally, contains mineral acids such as sulfuric or hydrochloric acid. Carbon Dioxide can exist in waters with pH values from 3.6 to 8.4, but will never be present in waters having a pH of 8.5 or above. The pH value is not a measurement of the amount of carbon dioxide in the water, but rather the relationship of carbon dioxide and bicarbonate alkalinity.

Treatment of Carbon Dioxide

Free CO2 can be easily dissipated by aeration. A two-column deionizer (consisting of a hydrogen form strong acid cation and a hydroxide form strong base anion) will also remove the carbon dioxide. The cation exchanger adds the hydrogen ion (H+), which shifts the above equation to the left in favor of water and carbon dioxide release. The anion resin removes the carbon dioxide by actually removing the bicarbonate ion. A forced draft degasifier placed between the cation and anion will serve to blow off the CO2 before it reaches the anion bed, thus reducing the capacity requirements for the anion resin. The CO2 can be eliminated by raising the pH to 8.5 or above with a soda ash or caustic soda chemical feed system.