When a sewage treatment plant is treating wastewater, the commonly used coagulants mainly fall into two categories: inorganic coagulants and organic coagulants. Inorganic coagulants include polyaluminium chloride (PAC), poly硫酸 ferric chloride, ferrous sulfate and basic aluminum chloride， etc. While organic coagulants include polyacrylamide (PAM)， chitosan coagulants and cationic polyamines， etc.
The effectiveness of these coagulants varies depending on the specific application scenario and the characteristics of the wastewater. For instance, polyaluminium chloride is an efficient inorganic polymer coagulant. Its flocs are large, the settling speed is fast, the dosage is low, and the cost is low. It can significantly remove suspended solids and colloidal substances from the wastewater. While polyacrylamide is a high-molecular coagulant, it has functions such as turbidity removal, color removal, and removal of heavy metal ions, and can quickly settle and filter the particles in the water.
In practical applications, a single flocculant may not be effective. It is necessary to use two or more flocculants in combination to enhance the flocculation effect. For instance, when anionic polyacrylamide and cationic polyacrylamide are used together, a better clarification effect can be achieved.