Coagulation and Flocculation Flashcards

What is the primary purpose of a jar test in water treatment?

Answer: To determine the optimal coagulant dose and pH

The jar test simulates the coagulation-flocculation process at bench scale to find the best coagulant dose and pH before full-scale application.

Zeta potential is used in water treatment to measure:

Answer: The surface charge of suspended particles

Zeta potential quantifies the electrokinetic charge on colloidal particles, indicating how well coagulation has neutralized particle charges.

Which of the following best describes 'sweep flocculation'?

Answer: Entrapping particles in a precipitate of metal hydroxide

Sweep flocculation occurs when excess metal coagulant forms a hydroxide precipitate that sweeps particles out of suspension as it settles.

Ferric sulfate as a coagulant is most advantageous over alum in water with:

Answer: High pH and low turbidity

Ferric sulfate performs better than alum at higher pH values because ferric hydroxide is less soluble over a wider pH range.

What effect does low water temperature have on flocculation?

Answer: It slows floc formation because water viscosity increases

Cold water is more viscous, which reduces particle collision frequency and slows floc growth, often requiring longer detention times or higher coagulant doses.

A flocculation basin's G value (velocity gradient) is typically maintained in what range?

Answer: 10–75 s⁻¹

Flocculation basins typically use a G value of 10–75 s⁻¹ to promote gentle particle collisions that build floc without shearing it apart.

Why is rapid mixing applied immediately after coagulant addition?

Answer: To disperse the coagulant uniformly throughout the water before hydrolysis products form

Rapid mixing must occur within milliseconds of coagulant addition to ensure uniform dispersion before metal hydrolysis products precipitate unevenly.