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Coagulation-flocculation is a physicochemical water treatment process in which charged colloidal particles that remain stably dispersed because of electrostatic repulsion are destabilized and then aggregated into larger settleable flocs [1]. In the coagulation stage, coagulants such as aluminum sulfate, ferric chloride, or cationic polymers are rapidly mixed into the water to neutralize the surface charge of the colloids, compress the electric double layer, and form microflocs; in the flocculation stage, gentle slow mixing promotes perikinetic and orthokinetic collisions among the destabilized particles so that they grow into dense, macroscopic flocs that can be removed by subsequent sedimentation and granular-media filtration [2]. The process is evaluated using standardized jar-test procedures that determine the optimal coagulant dose, pH, and mixing intensity, and its performance is governed by the surface chemistry of the suspended particles, the hydrolysis speciation of the added metal salts, and the mean velocity gradient generated by flocculation basin mixers [3].
References
- Letterman, R.D.; Amirtharajah, A.; O'Melia, C.R. Coagulation and flocculation. In Water Quality and Treatment, 5th ed.; Letterman, R.D., Ed.; McGraw-Hill: New York, NY, USA, 1999; Chapter 6.
- American Water Works Association. Operational Control of Coagulation and Filtration Processes, Manual M37, 3rd ed.; AWWA: Denver, CO, USA, 2011. ISBN: 1583210555.
- ASTM International. ASTM D2035-08 Standard Recommended Practice for Coagulation-Flocculation Jar Test of Water; ASTM International: West Conshohocken, PA, USA, 2008. https://store.astm.org/d2035-08.html.
