Coagulation (water treatment)

In water treatment, coagulation occurs when a coagulant is added to water to "destabilize" colloidal suspensions.

In a colloidal suspension, particles will settle very slowly or not at all because the colloidal particles carry surface electrical charges that mutually repel each other. A coagulant (typically a metallic salt) with the opposite charge is added to the water to overcome the repulsive charge and "destabilize" the suspension. For example, the colloidal particles are negatively charged and alum is added as a coagulant to create positively charged ions. Once the repulsive charges have been neutralized ( since opposite charges attract), the van der Waals force will cause the particles to cling together (agglomerate) and form micro floc. ^[1]

Conversely, flocculation involves the addition of polymers that clump the small, destabilized particles together into larger aggregates so that they can be more easily separated from the water. Flocculation is a physical process and does not involve the neutralization of charge. Coagulation may be used in conjunction with flocculation to assist with water clarification.

"...coagulation is one of the cheapest process for treatment of various organic effluents." ^[2]

See also

• Alum
• Aluminium sulfate
• Clarifying agent
• Colloid
• Dissolved air flotation
• Electrocoagulation
• Flocculation
• Industrial wastewater treatment
• Industrial water treatment
• Particle aggregation
• Polyaluminium chloride (PAC)
• Suspension (chemistry)
• Turbidity
• Ultrafiltration
• Water treatment

References

1. A. Koohestanian, M. Hosseini and Z. Abbasian (Babol Noshirvani University) (2008). "The Separation Method for Removing of Colloidal Particles from Raw Water" (PDF). American-Eurasian J. Agric. & Environ. Sci. 4 (2): 266–273. ISSN 1818-6769. See p. 267.
2. Pradeep Kumar, Tjoon Tow Teng, Shri Chand, and Kailas L. Wasewar (2011-08-20). "Treatment of Paper and Pulp Mill Effluent by Coagulation". International Scholarly and Scientific Research & Innovation 5 (8). p. 967. ...coagulation is one of the cheapest process[es] for treatment of various organic effluents.