Overview of the Ultrapure Water Coagulation and Flocculation Process and Principle

In water treatment, coagulation and flocculation are generally collectively referred to as coagulation. Coagulation typically refers to the process of using electrolytes to compress the electric double layer on the surface of particles and cause them to aggregate; flocculation refers to the process of using the "bridging" effect of polymeric substances to aggregate particles; while coagulation combines the two concepts, referring to the process of using inorganic electrolytes or organic polymeric substances to aggregate colloidal particles and tiny suspended solids in water.

This process is related to the properties of colloidal particles (including tiny suspended solids) in water, the hydrolysis of coagulants in water, and the interaction between colloidal particles and coagulants. However, in practical applications, especially in some ultrapure water treatment applications with special requirements, these three concepts are sometimes difficult to distinguish. In water treatment engineering practice, the mixing stage with added coagulants is considered the coagulation process, while the subsequent process is considered the flocculation process. The equipment for coagulation and flocculation is generally called a mixing tank and a flocculation tank (also called a reaction tank), respectively.

The purpose of the coagulation process is to change the properties and state of suspended solids such as clay and bacteria in water to facilitate their removal in subsequent processes. During flocculation, volumetric flocculation occurs, and the resulting large flocs are first removed by sedimentation in a settling device. Residual particles are then removed by filtration. When contact flocculation is used to remove suspended solids from water during filtration, the water treated by the coagulation process directly enters the rapid sand filter, eliminating the need for a settling device. This process is called direct filtration.