In regenerating ion-exchange systems and lowering the pH of water treated by membrane processes, which chemical family is used?

• A. Bases raise microfiltration
• B. Acids lower reverse osmosis membranes
• C. Bases raise reverse osmosis membranes
• D. Acids lower microfiltration

Answer: (B)

Acids are used in both regenerating ion-exchange systems and lowering pH in membrane-treated water. For ion-exchange regeneration, a strong acid is used to restore the resin to its H+ form by displacing the bound cations (like Ca2+ and Mg2+) with hydrogen ions, allowing the resin to be reused. In water treated by membrane processes such as reverse osmosis, lowering the pH with acid helps prevent carbonate scaling by shifting carbonate equilibria toward dissolved CO2, reducing the tendency for scale to form on the membrane surfaces. Because these two roles rely on acidic chemistry, acids are the appropriate chemical family. Bases would be used for other regeneration tasks (such as regenerating anion resins and raising pH), and microfiltration does not rely on acidifying the feed in the same way as RO pretreatment.