Which chemical family is used to regenerate ion-exchange systems and lower the pH of water treated by membrane processes?

• A. Acids
• B. Bases
• C. Salts
• D. Oxidants

Answer: (A)

Acids are used to regenerate ion-exchange systems and lower the pH of water treated by membrane processes. Ion-exchange resins exchange ions with the water, and after they become loaded with unwanted ions, they must be regenerated to their original form. Providing an acid supplies hydrogen ions that help displace the collected ions, restoring the resin’s regeneration state. In membrane-treated water, the permeate can be slightly alkaline, so adding acid brings the pH down to the desired level, which helps with corrosion control and downstream compatibility. Bases would raise pH, salts are mainly used to regenerate resins in a way that doesn’t directly lower pH, and oxidants are used for disinfection and oxidation rather than resin regeneration or pH adjustment.