What is a disadvantage of using caustic soda to soften hard water compared to other chemicals?

• A. More sludge
• B. Harder to store
• C. Harder to handle
• D. More expensive

Answer: (D)

Raising pH with caustic soda to soften water may work, but its cost is the main drawback. Sodium hydroxide is much more expensive per unit of hardness removed than lime or soda ash, which are the common alternatives for lime-soda softening. This higher chemical cost drives up operating expenses even if the chemical does the job effectively. Handling and storage safety are concerns with a highly caustic chemical, but they don’t outweigh the cost issue in most plant comparisons. So, the biggest disadvantage is the higher expense compared to other softening chemicals.