Surface chemistry In
colloid chemistry, flocculation refers to the process by which fine
particulates are caused to clump together into a floc. The floc may then float to the top of the liquid (creaming),
settle to the bottom of the liquid (
sedimentation), or be readily
filtered from the liquid. Flocculation behavior of soil colloids is closely related to freshwater quality. High dispersibility of soil colloids not only directly causes turbidity of the surrounding water but it also induces
eutrophication due to the adsorption of nutritional substances in rivers and lakes and even boats under the sea.
Physical chemistry For
emulsions, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity. Flocculation is thus the initial step leading to further ageing of the emulsion (droplet coalescence and the ultimate separation of the phases). Flocculation is used in mineral dressing, but can be also used in the design of physical properties of food and pharmaceutical products.
Medical diagnostics In a
medical laboratory, flocculation is the core principle used in various diagnostic tests, for example the
rapid plasma reagin test.
Civil engineering/earth sciences In
civil engineering, and in the
earth sciences, flocculation is a condition in which
clays, polymers or other small charged particles become attached and form a fragile
structure, a floc. In dispersed clay
slurries, flocculation occurs after mechanical agitation ceases and the dispersed clay platelets spontaneously form flocs because of attractions between negative face charges and positive edge charges.
Biology Flocculation is used in
biotechnology applications in conjunction with
microfiltration to improve the efficiency of biological feeds. The addition of synthetic flocculants to the
bioreactor can increase the average particle size making microfiltration more efficient. When flocculants are not added, cakes form and accumulate causing low cell viability. Positively charged flocculants work better than negatively charged ones since the cells are generally negatively charged.
Cheese industry Flocculation is widely employed to measure the progress of
curd formation in the initial stages of
cheese making to determine how long the curds must set. • FeSO4 (
iron(II) sulfate) • Al2(SO4)3 (
aluminium sulfate) • FeCl3 (
iron(III) chloride)
Brewing In the brewing industry flocculation has a different meaning. It is a very important process in
fermentation during the production of beer where cells form macroscopic flocs. These flocs cause the yeast to sediment or rise to the top of a fermentation at the end of the fermentation. Subsequently, the yeast can be collected (cropped) from the top (
ale fermentation) or the bottom (
lager fermentation) of the fermenter in order to be reused for the next fermentation.
Yeast flocculation is partially determined by the calcium concentration, often in the 50-100ppm range. Calcium salts can be added to cause flocculation, or the process can be reversed by removing calcium by adding
phosphate to form insoluble calcium phosphate, adding excess
sulfate to form insoluble calcium sulfate, or adding
EDTA to
chelate the calcium ions. While it appears similar to sedimentation in colloidal dispersions, the mechanisms are different.
Water treatment process 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. 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 ==