Selection of polyacrylamide

According to ionic characteristics, polyacrylamide can be divided into four types: non-ionic polyacrylamide, anionic polyacrylamide, cationic polyacrylamide and amphoteric polyacrylamide. According to the molecular weight, there are different specifications of molecular weight, ion degree, etc., and many models are derived. Faced with the market's messy specification system, it is really difficult to select the best polyacrylamide model for your own sewage system. How to deal with sewage or pollution? Frequently asked questions about the selection of mud polyacrylamide.

1. Understand the source of sludge

Sludge is an inevitable product in sewage treatment. First, we should understand the source, nature, composition and solid content of sludge. According to the main components of sludge, sludge can be divided into organic sludge and inorganic sludge.

Generally speaking, cationic polyacrylamide is used to treat organic sludge, and anionic polyacrylamide is used to treat inorganic sludge. It is not easy to use cationic polyacrylamide when it is very alkaline, and it is not suitable to use anionic polyacrylamide when it is very acidic. When the solid content of the mud is high, the amount of polyacrylamide is usually larger.

2. The ion degree selection of polyacrylamide

For the sludge to be dewatered, flocculants of different ionicity can be screened through small experiments to select the best and suitable polyacrylamide, so that the best flocculant effect can be obtained, and the dosage of chemicals can be minimized, saving costs . The key point of ion selection:

(1) The size of the floc

The size of the floc: too small a floc will affect the speed of drainage, too large a floc will bind more water and reduce the degree of mud biscuit. The size of the flocs can be adjusted by selecting the molecular weight of polyacrylamide.

(2) Floc strength (moisture content)

The strength of the flocs: the flocs should remain stable and not broken under shearing. Increasing the molecular weight of polyacrylamide or choosing a suitable molecular structure can help improve the stability of the flocculation.

(3) Mixing of polyacrylamide and sludge

Polyacrylamide must fully react with the sludge at a certain position of the dehydration equipment to cause flocculation. For this reason, the viscosity of the polyacrylamide solution must be appropriate, and it can be fully mixed with the sludge under the existing equipment conditions. Whether the two are uniformly mixed is a key factor for success. The viscosity of polyacrylamide solution is related to its molecular weight and concentration.

(4) Dissolution of polyacrylamide

The flocculation function can be fully exerted only when it is dissolved well. As mentioned earlier, the dissolution process of polyacrylamide is actually the maturation process of polyacrylamide. Sometimes it is necessary to speed up the dissolution rate. At this time, consider increasing the concentration of the polyacrylamide solution.

Therefore, the best product selection must be determined by laboratory beaker experiments.

3. Molecular weight selection of polyacrylamide

The molecular weight of polyacrylamide refers to the length of the molecular chain in the molecule. The molecular weight of polyacrylamide is between 5 and 18 million. Generally speaking, the higher the molecular weight, the greater the viscosity of the polyacrylamide product. However, the At this time, it is not that the higher the molecular weight of the product, the better the use effect. Specifically, in use, the appropriate polyacrylamide molecular weight should be determined according to the actual application industry, water quality, treatment equipment and other conditions.

Polyacrylamide is a high molecular weight coagulant. The products can be divided into low molecular weight (<1 million), medium molecular weight (2-4 million) and high molecular weight (>7 million) according to their average molecular weight.

Polyacrylamide is used in sewage treatment, a high molecular water-soluble organic polymer with a molecular weight of several million to tens of millions. Domestic polymer polyacrylamides include: non-ionic polyacrylamide (abbreviated as NPAM, molecular weight 8-15 million), anionic polyacrylamide (abbreviated as APAM, molecular weight 8-20 million), cationic polyacrylamide (abbreviated as CPAM, molecular weight 800 -12 million, ion degree 10%-80%).

When used as a coagulant only, generally the higher the molecular weight, the tighter the flocs, the more economical the use of drugs, but the molecular weight of anionic polyacrylamide is recommended not to exceed 20 million.

If in terms of sludge dewatering. When using a belt filter press, generally the molecular weight should not be too high. If the molecular weight is too high, it may block the filter cloth and affect the dehydration effect; for example, if you use a centrifugal filter press, the molecular weight requirement is higher because the centrifugal pressure The filter requires the floc to be able to withstand shear as much as possible, so choose a product with a relatively high molecular weight.

It can be seen from the above that the choice of molecular weight and ion degree is not absolute. It is best to do a selection test before selecting polyacrylamide, and it is best to run a computer operation test, so that the data obtained is the most accurate.