Introduction of Synthetic Organic Polymer Flocculants

Sewage treatment synthetic organic polymer flocculants are mostly polypropylene and polyethylene materials, such as polyacrylamide, polyethylene imine, etc.

The Types of Synthetic Organic Polymer Flocculants

Synthetic organic polymer flocculants are water-soluble linear polymers, and each macromolecule is composed of many repeating units containing charged groups, so they are also called polyelectrolytes.

Cationic polyelectrolytes contain positive groups, and anionic polyelectrolytes contain negative groups, which are called non-ionic polyelectrolytes.

At present, most polymer flocculants are anionic, and they can only play a role in assisting coagulation of negative colloidal impurities in water. It can not be used alone, but with aluminum salt and iron salt. Cationic flocculants can play the role of coagulation and flocculation at the same time and can be used alone, so they have been developed rapidly.

Polyacrylamide type non-ionic polymers are widely used, often combined with iron and aluminum salts. Satisfactory treatment effect is obtained by using the electric neutralization of iron and aluminum salts on colloidal particles and the excellent flocculation function of polymer flocculants. Polyacrylamide has the characteristics of small dosage, fast coagulation, large and strong floc particles in use.

Characteristics of Polyacrylamide Flocculants

Polyacrylamide(PAM) is one of the most widely used artificial synthetic organic polymer flocculants in sewage treatment, and sometimes it is also used as a coagulant aid.

The raw material for the production of polyacrylamide is polyacrylonitrile CH2=CHCN. Under certain conditions, acrylonitrile is hydrolyzed to generate acrylamide, which is then obtained through suspension polymerization. Polyacrylamide belongs to water-soluble resin, and its products include granular solid and viscous aqueous solution of certain concentration.

The actual existing form of polyacrylamide in water is random coil. Since the random coil has a certain particle size and some amide groups on its surface, it can play a corresponding role in bridging and adsorption, that is, it has a certain flocculation capacity.However, because the long chain of polyacrylamide is coiled into a linear group, its bridging range is small. After the two amide groups are concluded, they are equivalent to counteracting each other and losing two adsorption sites. In addition, part of the amide groups are stored inside the linear group structure, and cannot contact and absorb with the impurities in water, so their adsorption capacity cannot be fully exerted.

In order to separate the amide groups that are bound together again and expose the internal amide groups to the outside, people try to extend and unfold the random wire groups appropriately, and even try to add some groups with cations or anions on the long molecular chain, while improving the adsorption bridging ability and the role of neutralizing and compressing the double electric layer. In this way, a series of polyacrylamide flocculants or coagulant aids with different properties are derived on the basis of PAM.

For example, alkali is added to the polyacrylamide solution to convert the amide group on some chain links into sodium carboxylate, which is easy to dissociate sodium ions in water, leaving the COO group on the branch chain, thus generating partially hydrolyzed anionic polyacrylamide.

The COO group on the molecular structure of anionic polyacrylamide makes the molecular chain have a negative charge. They repel each other and pull apart the amide group that was originally contracted together, promoting the molecular chain to gradually extend from the linear group to the long chain, so as to expand the bridging range and improve the flocculation ability. As a coagulant aid, it has more outstanding advantages.

The use effect of anionic polyacrylamide is related to its "degree of hydrolysis". If the "degree of hydrolysis" is too small, the coagulation or coagulation aid effect will be poor, and if the "degree of hydrolysis" is too large, the production cost will be increased.

Sewage treatment flocculant is a non-toxic organic polymer flocculant with positive charge (active group), which can effectively coagulate suspended organic colloid and organic compound. The dosage concentration depends on the turbidity of raw water. The most appropriate dosage of flocculant shall be determined by the test of water sample. Too much or too little dosage will reduce the filtering effect.

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