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Synthetic polyelectrolytes are currently the most used ones in the industry on account of the following advantages: structuration according to specific requirements, greater purity, higher quality, stability and greater efficiency compared to natural ones; they do not add insoluble substances to the sludge, nor do they modify the physico-chemical properties of water and thus liquids may be recycled. The main action of these products is to bring together and agglutinate the flocs formed by the coagulant, thus obtaining a considerable increase in the size of the same and a subsequent increase in the settling rate speed, as well as an improvement in the quality of the effluent. Polyacrylamide shows high solubility in water, while it is insoluble in most other common organic liquids such as methanol, ethanol, acetone, diethyl ether, and aliphatic and aromatic hydrocarbons. Paradoxically, however, despite this highly hydrophilic character, the main technical application of polyacrylamide is for flocculation of aqueous suspension and related purposes, where it is therefore required to have a relatively high affinity to the surface of the suspended solid if the necessary strong adsorption of the polymer is to take place. In practice, however, this adsorption is often enhanced by using modified (anionic or cationic) forms of polyacrylamide. Polyacrylamide can be classified to three categories: non-ionic, anionic and cationic polyacrylamide.