Which treating process is described as lime - lime soda softening?

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Hardness removal by lime and lime soda softening works by precipitating calcium and magnesium as insoluble compounds after raising the water’s pH. Lime (calcium hydroxide) is added to increase alkalinity and convert bicarbonate hardness into carbonate form, which then precipitates as calcium carbonate. Magnesium tends to precipitate as magnesium hydroxide in the alkaline environment. Adding soda ash (sodium carbonate) helps supply carbonate ions to drive further precipitation of remaining calcium as calcium carbonate, making the process effective for waters with both temporary and permanent hardness. The result is clearer water with much of the hardness removed, achieved through controlled chemical precipitation and settling.

This differs from coagulation, which focuses on destabilizing and removing colloidal particles with coagulants; ion exchange, which swaps ions in solution for others using resin; and aeration, which mainly oxidizes contaminants and releases dissolved gases rather than removing hardness.