Flocculation
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| Name: | Flocculation |
| Category: | Separation technologies |
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Flocculation refers to the "reversible aggregation of colloidal particles to larger particles that can be filtered"[1]. Flocculation can be induced by adding "flocculants". The IUPAC Gold Book uses coagulation and flocculation as synonyms of agglomeration and defines agglomeration as a "process of contact and adhesion whereby dispersed particles are held together by weak physical interactions ultimately leading to phase separation by the formation of precipitates of larger than colloidal size."[2]
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Exemplary applications: 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 can form and accumulate causing low cell viability. Positively charged flocculants work better than negatively charged ones since the cells are generally negatively charged.
In the brewing industry flocculation 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 primarily 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 insolubable 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.
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| Technology name: | Technology category: | Pre-processing (Separation technologies), Post-processing (Separation technologies) | |
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References
- ↑ Peter W. Atkins, Loretta Jones, 2006: Chemie - einfach alles. Wiley-VCH, Weinheim.
- ↑ The International Union of Pure and Applied Chemistry (IUPAC), : IUPAC - agglomeration (except in polymer science) (A00182) , Last access January 31, 2022. https://goldbook.iupac.org/terms/view/A00182