Which statement correctly describes the effect of influent temperature on coagulation?

• A. Temperature has no effect on coagulation
• B. Higher temperature inhibits coagulation
• C. Higher temperature improves coagulation
• D. Temperature only affects disinfection

Answer: (C)

Coagulation depends on how fast colloids destabilize and form larger flocs, which is influenced by temperature. When influent temperature is higher, water becomes less viscous and molecular diffusion speeds up, so particles and coagulant molecules collide more readily. The chemical reactions that create effective coagulant hydrolysis products also proceed faster at warmer temperatures, helping destabilize colloids and grow flocs more efficiently. Additionally, the electrical double layer around particles thickens less at higher temperature, reducing repulsive forces and making aggregation easier. All this means coagulation works better in warmer water, and you can often achieve the same results with less coagulant or shorter mixing times. In colder water, slower kinetics and higher viscosity hinder collision rates, making coagulation less efficient.