Flocculation
| Technology | |
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| Technology details | |
| Name: | Flocculation |
| Category: | Pre-processing (Separation technologies), Post-processing (Separation technologies) |
| Feedstock: | Liquid phase with solid particles and, if applicable, flocculant |
| Product: | Solid phase (flocs) and liquid phase |
Flocculation refers to the "reversible aggregation of colloidal particles to larger particles that can be filtered"[1] or separated by sedimentation. 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]
Flocculation can be purposefully induced by adding flocculants. "Flocculants are agents that make fine and subfine solids or colloids suspended in the solution form large loose flocs through bridging, thus achieving solid-liquid separation."[3] Cells, for example, can be aggregated by adding multivalent cations, metal salts or polymers (for example, polyaluminum chloride).
Feedstock
Origin and composition
The feedstock would usually be the feed that shall be separated by flocculation and (if used) the chosen flocculant.
Pre-treatment
The flocculant can be stored in powder form or in a solution. "Most commercial flocculants are synthetic water soluble polymers with average molecular weights in the region 1000 to 30 × 106. They are generally supplied as powders that have a limited storage life, particularly when made up into solution."[4]
Process and technologies
The choice of the flocculant strongly depends on the desired outcome and the particles that shall be flocculated.
Flocculation of microalgae
For the flocculation of microalgae in wastewater, biopolymer flocculants can be used, as described in Microalgae-Based Biofuels and Bioproducts, 2017: "Polymer flocculants are polymers with charged functional groups. Polymer flocculants can induce flocculation by neutralizing the surface charge of particles or by forming bridges between individual particles. The functional groups should ideally be positively charged to allow for interactions with the negatively charged microalgal cells. Polymers are generally very effective at low dosages. In wastewater treatment, polyacrylamide-based flocculants are commonly used. Because they can contain potentially toxic acrylamide residues, flocculants based on natural biopolymers are preferred over synthetic polymers. An effective biopolymer flocculant for harvesting microalgae is chitosan, which is prepared by deacetylation of chitin. However, the cost of chitosan is relatively high due to its use in medical applications. Cheaper alternatives are cationic starch or tanfloc, which are, respectively, starch and tannins functionalized with quaternary ammonium groups."[5]
Exemplary applications
Improving fermentation feeds
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 usually work better than negatively charged ones since the cells are generally negatively charged.
Yeast flocculation
In the brewing industry flocculation is a very important process during the production of beer by fermentation 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 50–100 ppm 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.
Products
Post-treatment
After the flocculation process, usually the flocs are separated from the liquid phase. This separation can simply be the sedimentation of the flocs, but they can also be separated by other techniques like sieving, membrane filtration, collection of the flocs at the top layer etc.
Technology providers
| Company name | Country | Technology category | Technology name | TRL | Capacity [kg/h] | Processable volume [L] | Feedstock: Food waste | Feedstock: Garden & park waste |
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| Company 1 | [Country HQ location] | [Technology category (if different sub-categories are defined this has to be specified here, the available categories can be found on each technology page under the chapter Process and technologies)] | [Technology name (the "branded name" or the usual naming from company side)] | [4-9] | [numeric value] | ● | ● | |
| Company 2 | [Country HQ location] | [(if different sub-categories are defined this has to be specified here, the available categories can be found on each technology page under the chapter Process and technologies)] | [Technology name (the "branded name" or the usual naming from company side)] | [4-9] | [numeric value] | ● | ● |
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| Technology name: | Technology category: | Pre-processing (Separation technologies), Post-processing (Separation technologies) | |
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Open access pilot and demo facility providers
Patents
Currently no patents have been identified.
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
- ↑ Shuying Wang, Jinyang Fu, Cong Zhang, Junsheng Yang, 2021: Chapter 9 – Muck conditioning for EPB shield tunnelling and muck recycling – 9.3.1.5 Flocculants. Shield Tunnel Engineering : From Theory to Practice. {{{editor}}} (Ed.). Elsevier, Amsterdam, Netherlands.
- ↑ E. S. Tarleton, R.J. Wakeman, 2007: 3 – Pretreatment of suspensions. Solid/liquid separation : equipment selection and process design. {{{editor}}} (Ed.). Butterworth-Heinemann, Oxford.
- ↑ K. Muylaert, L. Bastiaens, D. Vandamme, L. Gouveia, 2017: 5 – Harvesting of microalgae: Overview of process options and their strengths and drawbacks – 5.3.5 Biopolymer flocculants. Microalgae-based biofuels and bioproducts : from feedstock cultivation to end-products. Cristina Gonzalez-Fernandez, Raúl Muñoz (Ed.). Woodhead Publishing, Kindlington, United Kingdom.