The pH and alkalinity test is the most significant test for establishing proper what for coagulated water?

• A. Chemical dosage
• B. Flow rate
• C. Turbidity
• D. Color

Answer: (A)

pH and alkalinity control how coagulants work in water. Coagulants hydrolyze to form positively charged species that neutralize the negative charges on tiny particles, allowing them to come together into larger flocs. The effectiveness of this neutralization depends on the pH, which determines the speciation of the hydrolysis products and the surface charge of particles. Alkalinity provides buffering and supplies carbonate/bicarbonate that dampens pH shifts and helps maintain the optimal environment for coagulation. If alkalinity is too low, dosing the coagulant can lower the pH too much, reducing coagulation efficiency and requiring more coagulant or additional buffering. Because pH and alkalinity directly influence how much coagulant is needed to achieve effective charge neutralization and floc formation, they are the most important parameters for establishing the proper chemical dosage.