When can raw water be normally softened using lime alone?

When can raw water be normally softened using lime alone?

• A. When it contains high noncarbonate hardness
• B. When it contains little or no noncarbonate hardness
• C. When it is free of calcium
• D. When it has a low pH

Answer: (B)

Raw water can normally be softened using lime alone when it contains little or no noncarbonate hardness. In water treatment, noncarbonate hardness mainly comes from sulfates and chlorides of calcium and magnesium, which do not precipitate with lime in the same way that carbonate hardness does. When lime is introduced to water that contains primarily carbonate hardness, calcium hydroxide reacts with the bicarbonate and carbonate ions to precipitate calcium carbonate, effectively softening the water. However, if noncarbonate hardness is present, especially in significant amounts, lime alone would not adequately address those hardness sources because noncarbonate hardness remains soluble and does not precipitate out even when lime is added. Hence, for effective softening using lime, the water should contain little or no noncarbonate hardness. This is critical for achieving the desired reduction in hardness levels and ensuring the treatment process is efficient.

Raw water can normally be softened using lime alone when it contains little or no noncarbonate hardness. In water treatment, noncarbonate hardness mainly comes from sulfates and chlorides of calcium and magnesium, which do not precipitate with lime in the same way that carbonate hardness does.

When lime is introduced to water that contains primarily carbonate hardness, calcium hydroxide reacts with the bicarbonate and carbonate ions to precipitate calcium carbonate, effectively softening the water. However, if noncarbonate hardness is present, especially in significant amounts, lime alone would not adequately address those hardness sources because noncarbonate hardness remains soluble and does not precipitate out even when lime is added. Hence, for effective softening using lime, the water should contain little or no noncarbonate hardness. This is critical for achieving the desired reduction in hardness levels and ensuring the treatment process is efficient.