The degree of treatment of water supply, sewage, and wastewater mainly depends on the flocculation characteristics of the microbial flocculant. Therefore, a better flocculation effect can be achieved through certain treatment conditions. However, there are many factors that affect the flocculation characteristics, and only by mastering the laws can the flocculation ability of the microbial flocculant be better utilized.
The influence of the characteristics of the microbial flocculant itself
The main components of microbial flocculants contain hydrophilic active groups, such as amino, hydroxyl, carboxyl, etc., so its flocculation mechanism is consistent with organic polymer flocculants (using the characteristics of their linear molecules to play a bonding and bridging role) Flocculate the particles) the same. The molecular weight of the microbial flocculant has a great influence on its flocculation effect. The larger the molecular weight, the better the flocculation effect. When the protein components of the flocculant are degraded, the molecular weight decreases and the flocculating activity decreases significantly. Generally, the flocculating effect of macromolecular flocculants with linear structure is better. If the molecular structure is cross-chain or branched-chain structure, its flocculation effect is poor.
The influence of the surface charge of colloidal particles
From the "bridging" theory and the "charge neutralization" theory, it is known that the flocculant macromolecules simultaneously adsorb multiple colloidal particles with the help of ionic bonds, hydrogen bonds and van der Waals forces, resulting in a "bridging" phenomenon between the particles, forming a three-dimensional network Like structure and settle down. Therefore, the surface charge of colloidal particles has an important effect on flocculation, and the oppositely charged polyelectrolyte can reduce the surface charge density of the particles, so that the particles can be close enough to each other to make the attractive force effective.
The flocculation effect of the microbial flocculant is affected by various reaction conditions such as sample amount, pH value, metal ions, temperature, stirring speed, and water quality. When using self-extracted microbial flocculant to treat dye wastewater, it is found that Ca2+ has the synergistic effect of promoting the formation of flocs and increasing the sedimentation rate. There are also literatures that the addition of salt in the system will reduce the flocculation activity of microorganisms, which may be due to the addition of Na+ that destroys the formation of hydrogen bonds between macromolecules and colloids. Because the formation of flocculation is a complex process, in order to better explain the mechanism, it is necessary to conduct a more in-depth study of the influence of specific flocculants and colloidal particles on their composition, structure, charge, conformation and various reaction conditions.