Why is caustic-soda softening not a popular process despite its effectiveness?

Caustic-soda softening is indeed effective in removing hardness from water, but it is not widely utilized primarily because it raises the total dissolved solids (TDS) in the treated water. This increase in TDS occurs because sodium ions, introduced during the softening process, contribute to the overall mineral content of the water.

Maintaining low TDS levels is crucial in water treatment systems, as high TDS can lead to potential issues such as scaling in pipes and equipment, negatively impacting the aesthetic quality of water, and causing health concerns based on specific ion concentrations. This makes caustic-soda softening less desirable, particularly when alternatives like lime softening can reduce hardness without significantly increasing TDS levels.

In contrast, while other options might describe valid aspects of different treatment processes, they do not capture the primary reason for the limited adoption of caustic-soda softening based on its impact on total dissolved solids in the treated effluent.