CO2 is typically used in the lime softening process.
In excess lime softening, lime is added to the water to combine with the free CO2, bicarbonate alkalinity, and magnesium. Then the precipitated calcium carbonate and magnesium hydroxide is settled out. The water is then recarbonated with CO2 to precipitate out the excess calcium hydroxide.
It is also used to make pH adjustments following filtration.
