Adding alum as a coagulant primarily affects which parameter?

Adding alum as a coagulant primarily affects which parameter?

• A. The surface charge (zeta potential) of particles.
• B. Water temperature.
• C. Dissolved oxygen.
• D. Turbidity.

Answer: (B)

Alum as a coagulant primarily affects the surface charge of particles, or zeta potential. The aluminum ions neutralize the negative charges on colloidal particles, reducing electrostatic repulsion between them. With this charge neutralized, particles can come together more easily to form larger flocs that settle out, which is the central way alum helps clarify water. Temperature, dissolved oxygen, or direct turbidity changes aren’t the primary targets of alum addition—the practical outcome is achieved by destabilizing particle charges and promoting floc formation that reduces turbidity.

Alum as a coagulant primarily affects the surface charge of particles, or zeta potential. The aluminum ions neutralize the negative charges on colloidal particles, reducing electrostatic repulsion between them. With this charge neutralized, particles can come together more easily to form larger flocs that settle out, which is the central way alum helps clarify water. Temperature, dissolved oxygen, or direct turbidity changes aren’t the primary targets of alum addition—the practical outcome is achieved by destabilizing particle charges and promoting floc formation that reduces turbidity.