Low alkalinity and coagulation can be addressed by addition of which chemical?

Low alkalinity and coagulation can be addressed by addition of which chemical?

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

Answer: (D)

When coagulation is being used, having enough alkalinity helps keep the pH in the right range and provides buffering so the coagulant can work effectively. Lime (calcium hydroxide) is the best choice because it raises both alkalinity and pH, and the calcium it supplies can aid floc formation and precipitation of calcium carbonate, improving the coagulation process and settling. Sodium hydroxide also raises pH and can add some alkalinity, but it doesn’t provide the same carbonate-based buffering and can alter water chemistry in less favorable ways for coagulation at typical doses. Activated carbon is for adsorbing organics and doesn’t affect alkalinity, and chlorine is a disinfectant, not a coagulant aid.

When coagulation is being used, having enough alkalinity helps keep the pH in the right range and provides buffering so the coagulant can work effectively. Lime (calcium hydroxide) is the best choice because it raises both alkalinity and pH, and the calcium it supplies can aid floc formation and precipitation of calcium carbonate, improving the coagulation process and settling.

Sodium hydroxide also raises pH and can add some alkalinity, but it doesn’t provide the same carbonate-based buffering and can alter water chemistry in less favorable ways for coagulation at typical doses. Activated carbon is for adsorbing organics and doesn’t affect alkalinity, and chlorine is a disinfectant, not a coagulant aid.