Aqvo
Industrial

Under the action of flocculants, three-dimensional structures are formed between colloidal particles, capable of faster and more complete separation of liquid phases. The reason for the appearance of such structures is the adsorption of flocculant macromolecules on several particles with the formation of polymer bridges between them. Thus, flocculation is a process in which there is an adsorption interaction of a particle of wastewater pollution with macromolecular substances (flocculating agents).

At the same time, in the process of flocculation, the process of flocculation occurs (during the interaction of macromolecular substances with particles in the treated wastewater), with the formation of aggregates (flakes, complexes) having a three-dimensional structure.
The adsorption process occurs in two stages: first, each macromolecule is attached by several segments to one particle (primary adsorption), then the free segments are attached to the surface of other particles, linking them with polymeric bridges (secondary adsorption). There are various mechanisms for fixing macromolecules of flocculants on the surface of particles.

Non-ionic polyelectrolytes attach to particles with the help of polar groups (most often hydroxyl) due to the formation of hydrogen bonds between the hydrogen of the hydroxyl and oxygen, nitrogen and other atoms located on the surface of the particles. The presence of hydrogen bonds has been established experimentally using infrared spectroscopy. Although the hydrogen bond energy is much less than the chemical bond energy, a large number of hydroxyl groups contributes to the strong fixation of the flocculant molecules. Anionic flocculants are able to be fixed on the surface of particles not only with the help of hydrogen bonds, but also due to the chemical interaction (chemisorption) of anions with cations located on the particle surface.

Cationic polyelectrolytes, in addition to the formation of aggregates by mechanisms similar to those described above, promote flocculation due to the neutralization of the negative charge of the particles. Flocculants are water-soluble linear polymers consisting of a large number of groups. The chain length can be up to 1 micron. Molecular the mass of flocculants can reach several million, the degree of polymerization – several thousand. In wastewater treatment technology, flocculants are usually used in addition to mineral coagulants, since they contribute to the expansion of optimal coagulation areas (in terms of pH and temperature), increase the density and strength of the resulting flakes, reduce the consumption of coagulants, and increase the reliability and productivity of wastewater treatment facilities. The addition of a flocculant to the treated waste water increases the rate of occurrence and subsequent settling of flocs that occur during coagulation.

At the same time, the sediment density increases, and the action of coagulant substances becomes effective in a wider pH range of treated wastewater. If the treated wastewater contains a large amount of suspended particles, then their sedimentation can only be ensured with the help of flocculants, without the use of coagulation agents. Flocculation in wastewater treatment processes, can be used in the following cases:

wastewater treatment of suspended solids biochemical oxygen demand in primary clarifiers conditioning of wastewater containing certain industrial wastes improvement of the performance of secondary clarifiers following the activated sludge treatment as a pretreatment step for filtration of secondary industrial wastes Flocculation can be carried out in separate tanks or tanks specially designed for this purpose

in pipelines connecting wastewater treatment equipment, or in combination with a flocculator. Flocculation usually follows rapid agitation in which chemicals are added to unstable particles. The destabilization of particles that occurs as a result of the addition of chemical reagents is called coagulation.

There are two types of flocculation: microflocculation macroflocculation They differ in particle size. Microflocculation is the term used when when it is necessary to refer to the accumulation of particles resulting from the random thermal movement of the molecules of a liquid, known as Brownian motion. Microflocculation makes it possible to remove particles from wastewater whose sizes range from 0.001 to 1 micron. Macroflocculation is used when the particle size of the wastewater to be treated exceeds 1 micron. Macroflocculation can be achieved with a forced velocity gradient and uneven settling. Particles in the waste liquid can be combined together (flocculate) by means of a forced velocity gradient.
Fast moving particles will achieve slow moving velocities in the field. If the colliding particles aggregate, then a larger particle is formed, which is easier to remove from the wastewater by gravity separation. In the case of macroflocculation due to non-uniform settling, larger particles reach smaller particles in the process of gravity deposition.

When two particles collide and stick together, a larger particle is formed, which is deposited in the treated wastewater at a higher rate than the original particles. Thus, flocculants are effective reagents used in the thickening of effluents in the clarification process. The use of new effective reagents, technological processes and equipment can significantly increase productivity, improve the quality of industrial wastewater treatment with minimal use of production capacity.