Flocculation

Technology
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" 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."

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." 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."

Process and technologies

The choice of the flocculant strongly depends on the desired outcome and the particles that shall be flocculated.

Flocculation of microalgae

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."

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

Technology comparison

Company name	Country	Technology subcategory	Technology name	TRL	Capacity [kg/h]	Processable volume [L]	Feedstock: Food waste	Feedstock: Garden & park waste
Dewlink	United Kingdom	-	Tubox® & Swingmill®	9	-	-	●	●
MVest Water	Norway	-	NORWAFLOC® / NORWAPOL	9	-	-	●	●

Dewlink

Flocculation provider

General information
Company:	Dewlink Sludge Treatment Ltd.
Country:	United Kingdom
Contact:	info@dewlink.com
Webpage:	https://dewlink.com
Technology and process details
Technology name:	Tubox® (Mixing tank with high speed mixing tube, creating a collision effect leading to faster flocculation) & Swingmill®	Technology category:	Pre-processing (Separation technologies), Post-processing (Separation technologies)
TRL:	9	Capacity:	kg·h-1
Agitator:	High-speed mixing blade	Processable volume:	L
Reactor:		Separation type:	Flocculation
		Other:
Feedstock and product details
Feedstock:	Sludge (Waste Activated Sludge, DAF Sludge, Chemical Sludge, Digested Sludge, Raw Sludge)	Product:	Sludge / dewatered sludge and water

Founded in Telford UK, DEWLINK SLUDGE TREATMENT LTD provides a simple and cost effective method of dewatering sludge and wastewater from many industrials.

The three main stages of sludge dewatering process (polymer dissolution, flocculation and dewatering) are indispensable.

We have used these processes as the main focus for our dewatering products. With our attention to details and the drive for perfection, we have developed a new system which is more efficient, stable, economical, intelligent, secure, convenient and environmentally friendly. This is a technical innovation in the solid-liquid separation industry and we believe this will change the pattern of the industry, promoting further development of technologies.

MVest Water

Flocculation provider

General information
Company:	MVest Water
Country:	Norway
Contact:	info@mvestwater.com
Webpage:	https://mvestwater.com
Technology and process details
Technology name:	NORWAFLOC® (Natural & biodegradable flocculant/coagulant, combined into one product) / NORWAPOL (Polishing filtration process)	Technology category:	Pre-processing (Separation technologies), Post-processing (Separation technologies)
TRL:	9	Capacity:	kg·h-1
Agitator:		Processable volume:	L
Reactor:		Separation type:	Flocculation, filtration
		Other:
Feedstock and product details
Feedstock:	Wastewater from aquaculture, from fish slaughterhouse, sludge, wastewater from agriculture, from food & beverage industry	Product:	Potable water

M Vest Water is a leader in the development of high performance and environmentally responsible “green” water and wastewater treatment products and processes. The company was incorporated in 2017 by Norwegian Water Technologies AS and M Vest Invest AS. We have a singular and clear-cut mission: to realize a zero-discharge future. With our disruptive technology, we are already making significant strides towards achieving this goal.

NORWAFLOC^®, a natural polymer flocculant, is our flagship product. Its combination of both natural polysaccharide-based flocculants and a highly charged coagulant in a single product means that it can be applied in just one dosing step. The combination of a biodegradable, natural polymer with a highly charged coagulant leads to a completely natural product that achieves even better results compared to traditional synthetic polymers or other biopolymers.

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