The control of pH plays a key role in the quality of drinking water. When it’s too high, carbon dioxide (CO2) can be added to the raw water. The pH falls off slightly, permitting subsequently added flocculants to maximize their purification performance. The carbon dioxide produces no byproducts whatsoever that might alter the water quality. Stronger mineral acids could also be used, but they leave chloride and sulfur residuals, while CO2 raises the salt content less.
CO2 also provides other benefits: The alkalinity, another important aspect of drinking water quality, is not disturbed – unlike with mineral acids. The addition of CO2 maintains the equilibrium between corrosion-inducing ions such as chlorides and sulfates and corrosion-inhibiting hydrogen carbonate. Carbon dioxide is more economical than mineral acids, because smaller quantities are needed. The storage and handling of CO2 are also easier and less dangerous.