What is the difference between coagulation and flocculation?

Coagulation and flocculation are two essential processes used in water treatment to remove impurities and particles from water. While they are related and often used in conjunction, they serve slightly different purposes:

Coagulation:

Coagulation is the initial step in water treatment, where chemical coagulants are added to the water. The most common coagulants are Aluminum Sulfate (alum) and ferric chloride. These chemicals are added to destabilize the charged particles (colloids) present in the water.

The coagulants work by neutralizing the electrical charges on these particles. Particles in water typically have a negative charge, and the coagulants introduce positively charged ions. This neutralization reduces the electrostatic repulsion between particles, allowing them to come closer together.

As a result of coagulation, small particles start to clump together, forming larger, heavier particles known as flocs. These flocs are not yet large enough to settle out of the water by gravity alone, but they are easier to handle in subsequent treatment processes.

Flocculation:

Flocculation follows coagulation in the water treatment process. It involves gently stirring or agitating the water to encourage the smaller floc particles to collide and combine into larger and heavier flocs.

Flocculation helps promote the formation of larger, denser flocs that can more effectively settle out of the water. These larger flocs are easier to separate from the treated water.

During the flocculation process, additional chemicals called flocculants may be added to aid in the agglomeration of flocs. Common flocculants include polymers.

In summary, coagulation is the process of chemically destabilizing particles in water by neutralizing their charges, while flocculation is the physical process of bringing these destabilized particles together to form larger flocs. Together, coagulation and flocculation help to clarify water by making it easier to remove suspended particles and impurities through subsequent processes such as sedimentation and filtration in water treatment plants.

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