What membrane process will remove hardness?

What membrane process will remove hardness?

• A. Nanofiltration and reverse osmosis
• B. Nanofiltration and ultrafiltration
• C. Ultrafiltration and microfiltration
• D. Reverse osmosis and ultrafiltration

Answer: (A)

Hardness comes from dissolved minerals like calcium and magnesium salts, so removing hardness requires a membrane that rejects dissolved ions. Reverse osmosis provides the strongest ion rejection, removing most dissolved minerals and giving very low hardness. Nanofiltration also effectively reduces hardness by rejecting many divalent ions (Ca2+, Mg2+), while still allowing some monovalent ions through. Ultrafiltration and microfiltration, with their larger pore sizes, mainly remove suspended solids and larger organics, not dissolved salts, so they don’t meaningfully lower hardness. Therefore, using both nanofiltration and reverse osmosis targets the dissolved ions responsible for hardness, making this combination the best option.

Hardness comes from dissolved minerals like calcium and magnesium salts, so removing hardness requires a membrane that rejects dissolved ions. Reverse osmosis provides the strongest ion rejection, removing most dissolved minerals and giving very low hardness. Nanofiltration also effectively reduces hardness by rejecting many divalent ions (Ca2+, Mg2+), while still allowing some monovalent ions through. Ultrafiltration and microfiltration, with their larger pore sizes, mainly remove suspended solids and larger organics, not dissolved salts, so they don’t meaningfully lower hardness. Therefore, using both nanofiltration and reverse osmosis targets the dissolved ions responsible for hardness, making this combination the best option.