Which analyses are most significant for establishing chemical dosages for coagulation?

• A. Alkalinity and pH analyses
• B. Temperature analyses
• C. Turbidity analyses
• D. Conductivity analyses

Answer: (A)

Coagulation dosing hinges on how the water’s buffering capacity and its pH shape the chemical reactions that destabilize particles. Alkalinity measures the water’s ability to neutralize acids and to resist pH changes when coagulants are added. If alkalinity is low, the acidity produced by hydrolysis of coagulants can drop the pH too much, moving the chemistry away from the most effective form of the coagulant and making dosing unpredictable. Adequate alkalinity helps keep pH in a range where the hydrolysis products that promote charge neutralization and floc formation are most effective, so you can achieve the desired coagulation with a reliable dose.

pH itself controls the speciation of those hydrolysis products. Different pH levels favor different charged species, which directly affects how well the coagulant neutralizes negative colloidal charges and forms stable flocs. Because pH and alkalinity together dictate the actual chemical activity of the coagulant in water, analyzing them gives the best guidance for dosing.

Temperature, turbidity, and conductivity influence process performance in various ways, such as reaction rate or how well flocs settle, but they don’t determine the dose as directly as alkalinity and pH do.