Editing Flocculation (section)

=== Water treatment process ===
[[File:The coagulation and filtration processes at a drinking water treatment plant. (14868618507).jpg|thumb|Coagulation-flocculation process in a water treatment system]]
Flocculation and [[sedimentation (water treatment)|sedimentation]] are widely employed in the [[water purification|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.<ref>{{Cite web |url = http://app.knovel.com/hotlink/toc/id:kpWTPME003/water-treatment-process/water-treatment-process |title=Water Treatment Process Monitoring and Evaluation |date=2014-04-17 |access-date=2015-10-14 |website = Knovel |publisher = American Water Works Association (AWWA) |last = Beverly |first = Richard P}}</ref> 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.<ref name="Engelhardt" /> A variety of salts may be added to adjust the pH and act as [[clarifying agent]]s, 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]].<ref name="Engelhardt" />  A variety of [[cationic]], [[anionic]], and [[non-ionic]] [[polymer]]s are also used, typically with a [[molecular weight]] below 500,000.<ref name="Engelhardt" /> [[Polydiallyldimethyl ammonium chloride]] (polyDADMAC) and epiDMA (a [[copolymer]] of [[epichlorohydrin]] and [[dimethylamine]]) are common choices, though these can produce carcinogenic [[nitrosamine]]s.<ref name="Engelhardt" /> Sand, powerdered [[activated carbon]], and clay may also be used as [[nucleating agents]]; in some cases, these are re-used after extraction.<ref name="Engelhardt">{{cite web |title=Coagulation, Flocculation and Clarification of Drinking Water |author=Terry L. Engelhardt |date=April 2010 |url=https://sswm.info/sites/default/files/reference_attachments/ENGELHARDT%202010%20Coagulation%20Flocculation%20and%20Clarification.pdf}}</ref>

Biopolymers, especially, [[chitosan]], are increasingly popular as environmentally friendly flocculants.<ref>{{Cite journal |last1=Lamanna |first1=Leonardo |last2=Giacoia |first2=Gabriele |last3=Friuli |first3=Marco |last4=Leone |first4=Gabriella |last5=Carlucci |first5=Nicola |last6=Russo |first6=Fabrizio |last7=Sannino |first7=Alessandro |last8=Demitri |first8=Christian |date=2023-06-13 |title=Oil–Water Emulsion Flocculation through Chitosan Desolubilization Driven by pH Variation |journal=ACS Omega |language=en |volume=8 |issue=23 |pages=20708–20713 |doi=10.1021/acsomega.3c01257 |issn=2470-1343 |pmc=10268613 |pmid=37332801}}</ref> 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.<ref>{{Cite journal |last1=Pal |first1=Preeti |last2=Pal |first2=Anjali |last3=Nakashima |first3=Kazunori |last4=Yadav |first4=Brijesh Kumar |date=2021-03-01 |title=Applications of chitosan in environmental remediation: A review |url=https://www.sciencedirect.com/science/article/pii/S0045653520331313 |journal=Chemosphere |volume=266 |pages=128934 |doi=10.1016/j.chemosphere.2020.128934 |pmid=33246700 |bibcode=2021Chmsp.26628934P |issn=0045-6535|url-access=subscription }}</ref> 

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.<ref>{{Cite journal |last=Kazaz |first=Billur |date=July 2021 |title=State-of-the-Practice Review on the Use of Flocculants for Construction Stormwater Management in the United States |url=https://journals.sagepub.com/doi/10.1177/0361198121995192 |journal=Transportation Research Record |volume=2675 |issue=7 |pages=248–258 |doi=10.1177/0361198121995192 |via=Sage|url-access=subscription }}</ref>