Question

a groundwater source contains high carbonate hardness with negligible non-carbonate hardness. which treatment process is the most appropriate?

• soda ash softening only
• lime softening only
• sodium ion exchange followed by regeneration
• chlorination followed by filtration

Explanation:

Analyze the water quality characteristics

• Groundwater contains high carbonate hardness (associated with \(Ca^{2+}\) and \(Mg^{2+}\) bicarbonates).
• Non-carbonate hardness (associated with sulfates, chlorides, etc.) is negligible.

Evaluate treatment processes for carbonate hardness

• Lime (\(Ca(OH)_2\)) reacts with carbonate hardness to precipitate calcium carbonate (\(CaCO_3\)) and magnesium hydroxide (\(Mg(OH)_2\)).
• Soda ash (\(Na_2CO_3\)) is specifically required to remove non-carbonate hardness by providing carbonate ions.
• Since non-carbonate hardness is negligible, soda ash is not required.

Determine the most appropriate process

• Lime softening alone is sufficient and the most cost-effective method to remove high carbonate hardness when non-carbonate hardness is negligible.

Answer:

• Soda ash softening only
• Lime softening only (Correct answer)
• Sodium ion exchange followed by regeneration
• Chlorination followed by filtration