In the lime-soda ash softening process, the soda ash dosage is based on what?

In the lime-soda ash softening process, the soda ash dosage is based on the amount of noncarbonate hardness to be removed. This is important because soda ash (sodium carbonate) specifically targets noncarbonate hardness, which consists primarily of magnesium and calcium salts that do not precipitate out as a result of lime addition alone.

When lime is added to water, it helps to precipitate out carbonate hardness by converting calcium bicarbonate into calcium carbonate, which then settles out. However, to effectively address noncarbonate hardness, soda ash is used to react with the magnesium and any remaining calcium. The amount of soda ash required is directly related to the concentration of these noncarbonate hardness components in the water.

Calculating the dosage in this manner ensures that enough soda ash is added to effectively soften the water, reducing the overall hardness and making it more suitable for various applications, such as drinking water supply or industrial processes. Recognizing this relationship is critical for efficient treatment and preventing excess or inadequate dosages that could impact water quality or treatment costs.