What is the purpose of recarbonation after lime-soda ash softening?

Recarbonation is a crucial step following lime-soda ash softening in water treatment. The primary purpose of this process is to adjust the pH of the softened water, specifically to decrease it after the addition of lime, which raises pH levels significantly. By introducing carbon dioxide into the water during recarbonation, it reacts with the calcium hydroxide created during the lime-soda ash process. This reaction facilitates the formation of calcium carbonate, which precipitates out of the solution, effectively removing excess mineral content, primarily calcium ions and magnesium ions that could contribute to hardness.

Additionally, while enhancing flavor or increasing alkalinity may have some relevance, they are secondary effects rather than the main objective. The focus of recarbonation is on improving water quality by managing the pH and ensuring that any remaining hardness particles are effectively removed by precipitation. Therefore, the removal of suspended calcium carbonate, resulting from the recarbonation process, is indeed a core purpose of the step.