What type of hardness is treated by adding lime?

• A. Carbonate hardness
• B. Non-carbonate hardness
• C. General hardness
• D. Aesthetic hardness

Answer: (B)

The treatment of hardness in water by adding lime specifically targets carbonate hardness. This type of hardness is primarily caused by the presence of dissolved calcium and magnesium bicarbonates and is often referred to as temporary hardness. Lime, which is calcium hydroxide, reacts with the bicarbonates in the water, leading to precipitation of calcium carbonate, thus reducing the hardness.

By adding lime, the carbonate hardness can be converted into insoluble compounds that can be removed from the water. Non-carbonate hardness, on the other hand, is often due to soluble calcium and magnesium sulfates or chlorides, which remain in solution and are not typically addressed through lime addition. Understanding the differences among these types of hardness is crucial for effective water treatment, as they require different approaches for removal or reduction.