Anionic polyacrylamide is a kind of linear polymer, and molecular weight is the most important index of anionic polyacrylamide. Molecular weight refers to the relative molecular weight. For anionic polyacrylamide, the higher the molecular weight, the longer the molecular chain, the higher the degree of hydrolysis, the faster the dissolution rate, and the higher the viscosity of polyacrylamide solution. Therefore, the flocs formed in the process of sewage treatment are larger and more compact, and the settling speed is faster. But not all wastewater treatment must choose high molecular weight polyacrylamide. If the concentration of pollutants in raw water is low, high molecular weight polyacrylamide will make the raw water more turbid. Anionic polyacrylamide is mainly with negative charge, so it is better for wastewater with high pH neutral to alkaline inorganic content. However, for different industries, the type and dosage used for treating one ton of wastewater are very different. For example, for steel-making industry, anionic PAM with molecular weight of 10 million can be used, and the amount of sewage per ton is 3-5g; for automobile sewage treatment, anionic PMA with molecular weight of 12 million-15 million is recommended, and the amount of sewage per ton is 4-5g; for bentonite production, viscosity increasing, gold mining and other industries, anionic PMA with molecular weight of 15 million-18 million can be used, and the amount of sewage per ton is 2-3g.

As the molecular chain of PMA solution is easy to break and degrade when it is lower than 2 ℃ or higher than 55 ℃, the prepared solution should be used as soon as possible within 36 hours.