___ is the most significant test for establishing chemical dosages for coagulation.

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

Answer: (D)

pH and alkalinity set the conditions for how coagulants behave and how they neutralize particle charges. The amount of coagulant needed to destabilize colloids depends on how the coagulant hydrolyzes, and hydrolysis is highly sensitive to pH. Alkalinity provides the buffering that keeps pH in that favorable range during dosing; when coagulants hydrolyze, they consume alkalinity and can drive pH down, moving the system away from optimal coagulation. Because alkalinity and pH directly control the chemistry of coagulant species and the stability of the water, they are the best indicators for selecting the proper dose.

Temperature affects reaction rates but not the fundamental dose relationship, turbidity tells you how cloudy the water is rather than the exact dose needed, and conductivity indicates ionic content without dictating the coagulation dose.