Low alkalinity can undermine coagulation; which corrective action is commonly used?

Low alkalinity can undermine coagulation; which corrective action is commonly used?

• A. Sodium hydroxide
• B. Activated carbon
• C. Chlorine
• D. Lime

Answer: (D)

Alkalinity provides buffering during coagulation, helping keep the pH in the range where coagulants work best. When alkalinity is low, the pH can swing downward as the coagulant reacts, reducing floc formation and overall treatment effectiveness. The common corrective action is to add lime (calcium hydroxide). Lime raises both alkalinity and pH in a controlled way, which stabilizes the pH during coagulation and enhances the performance of coagulants like alum. It also supplies calcium, which can aid floc formation and settling. Other additives don’t address alkalinity in the same effective way: sodium hydroxide would push pH up but isn’t as reliable for restoring buffering capacity with coagulation; activated carbon targets organics; chlorine is for disinfection.

Alkalinity provides buffering during coagulation, helping keep the pH in the range where coagulants work best. When alkalinity is low, the pH can swing downward as the coagulant reacts, reducing floc formation and overall treatment effectiveness. The common corrective action is to add lime (calcium hydroxide). Lime raises both alkalinity and pH in a controlled way, which stabilizes the pH during coagulation and enhances the performance of coagulants like alum. It also supplies calcium, which can aid floc formation and settling. Other additives don’t address alkalinity in the same effective way: sodium hydroxide would push pH up but isn’t as reliable for restoring buffering capacity with coagulation; activated carbon targets organics; chlorine is for disinfection.