Why is pH control important in coagulation and disinfection?

Why is pH control important in coagulation and disinfection?

• A. It affects coagulation efficiency and disinfectant effectiveness, and helps control corrosion.
• B. It has no effect on disinfection.
• C. It only affects taste.
• D. It increases water hardness.

Answer: (A)

pH control matters because it directly affects both how well coagulation works and how effectively disinfectants can do their job. For coagulation, the charge of particles and the speciation of coagulants change with pH, so staying in an optimal pH range helps coagulants neutralize particle charges and form larger, settleable flocs. For disinfection, the dominant disinfecting species depends on pH: hypochlorous acid (HOCl) is a stronger disinfectant and is more prevalent at lower pH, while at higher pH more hypochlorite ion (OCl−) forms, which is less effective. In addition, pH influences corrosion and scaling in the distribution system, so maintaining the right pH helps protect pipes and minimize corrosion-related issues. Taken together, pH control enhances both removal of contaminants through coagulation and the effectiveness of disinfection, while also supporting corrosion control.

pH control matters because it directly affects both how well coagulation works and how effectively disinfectants can do their job. For coagulation, the charge of particles and the speciation of coagulants change with pH, so staying in an optimal pH range helps coagulants neutralize particle charges and form larger, settleable flocs. For disinfection, the dominant disinfecting species depends on pH: hypochlorous acid (HOCl) is a stronger disinfectant and is more prevalent at lower pH, while at higher pH more hypochlorite ion (OCl−) forms, which is less effective. In addition, pH influences corrosion and scaling in the distribution system, so maintaining the right pH helps protect pipes and minimize corrosion-related issues. Taken together, pH control enhances both removal of contaminants through coagulation and the effectiveness of disinfection, while also supporting corrosion control.