4.5 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Flocculation | 2/2 | https://en.wikipedia.org/wiki/Flocculation | reference | science, encyclopedia | 2026-05-05T10:47:51.876651+00:00 | kb-cron |
Flocculation and sedimentation are widely employed in the purification of drinking water as well as in sewage treatment, storm-water treatment and treatment of industrial wastewater streams. For drinking water, typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection. The coagulation and flocculation steps are similar, causing particles to aggregate and fall out of solution, but may use different chemicals or physical movement of water. A variety of salts may be added to adjust the pH and act as clarifying agents, depending on the water chemistry. These include sodium hydroxide, calcium hydroxide, aluminum sulfate, aluminum oxide, ferric sulfate, ferric chloride, sodium aluminate, with flocculant aids polyaluminum chloride, polyferric chloride. A variety of cationic, anionic, and non-ionic polymers are also used, typically with a molecular weight below 500,000. Polydiallyldimethyl ammonium chloride (polyDADMAC) and epiDMA (a copolymer of epichlorohydrin and dimethylamine) are common choices, though these can produce carcinogenic nitrosamines. Sand, powerdered activated carbon, and clay may also be used as nucleating agents; in some cases, these are re-used after extraction. Biopolymers, especially, chitosan, are increasingly popular as environmentally friendly flocculants. Chitosan is not only biodegradable but also exhibits a unique ability to bind with a wide range of contaminants, including heavy metals and organic pollutants, effectively removing them from water sources. Flocculation provides promising results for removing fine particles and treating stormwater runoff from transportation construction projects, but are not used by most state departments of transportation in the U.S. This may be due to regulative restrictions or insufficient guidance for soil sampling requirements in light of changing soil characteristics. States that must achieve a numeric turbidity limit are more inclined to use flocculants to ensure the appropriate level of treatment.
== Deflocculation ==
Deflocculation is the opposite of flocculation, sometimes known as peptization. Sodium silicate (Na2SiO3) is a typical example. Usually, in higher pH ranges, in addition to low ionic strength of solutions and domination of monovalent metal cations, the colloidal particles can be dispersed. The additive that prevents the colloids from forming flocs is called a deflocculant. For deflocculation imparted through electrostatic barriers, the efficacy of a deflocculant can be gauged in terms of zeta potential. According to the Encyclopedic Dictionary of Polymers deflocculation is "a state or condition of a dispersion of a solid in a liquid in which each solid particle remains independent and unassociated with adjacent particles (much like emulsifier). A deflocculated suspension shows zero or very low yield value". Deflocculation can be a problem in wastewater treatment plants, as it commonly causes problems with sludge settling and deterioration of the effluent quality.
== See also ==
== References ==
== Further reading == John Gregory (2006), Particles in water: properties and processes, Taylor & Francis, ISBN 1-58716-085-4 John C. Crittenden, R. Rhodes Trussell, David W. Hand, Kerry J. Howe, George Tchobanoglous (2012), MWH's water treatment: principles and design, third edition, John Wiley & Sons, ISBN 978-0-470-40539-0 Thomas, D.N.; Judd, S.J.; Fawcett, N. (May 1999). "Flocculation modelling: a review". Water Research. 33 (7): 1579–1592. Bibcode:1999WatRe..33.1579T. doi:10.1016/S0043-1354(98)00392-3. Watanabe, Yoshimasa (May 2017). "Flocculation and me". Water Research. 114: 88–103. Bibcode:2017WatRe.114...88W. doi:10.1016/j.watres.2016.12.035. PMID 28229952. Gregory, John; O'Melia, Charles R. (January 1989). "Fundamentals of flocculation". Critical Reviews in Environmental Control. 19 (3): 185–230. Bibcode:1989CRvEC..19..185G. doi:10.1080/10643388909388365. Brostow, Witold; Pal, Sagar; Singh, Ram P. (September 2007). "A model of flocculation". Materials Letters. 61 (22): 4381–4384. Bibcode:2007MatL...61.4381B. doi:10.1016/j.matlet.2007.02.007. Camp, Thomas R. (January 1955). "Flocculation and Flocculation Basins". Transactions of the American Society of Civil Engineers. 120 (1): 1–16. doi:10.1061/TACEAT.0007139.