Coagulants and Flocculants: Key Technologies for Suspended Solid Removal

Suspended solids and colloidal substances are common pollutants in natural water and industrial wastewater, which not only affect water clarity but also interfere with subsequent treatment processes. Coagulants and flocculants are the most widely used chemicals for removing these pollutants, and their performance directly determines the efficiency of solid-liquid separation in water treatment. This article focuses on the types, working mechanisms, and application precautions of coagulants and flocculants.

Coagulants are mainly divided into inorganic coagulants and organic coagulants. Inorganic coagulants, such as aluminum sulfate, ferric chloride, and polyaluminum chloride (PAC), are low-cost and widely used. They work by hydrolyzing in water to produce positively charged ions, which neutralize the negative charge on the surface of colloidal particles, destroying the stability of colloids and promoting their aggregation. Organic coagulants, including polyacrylamide (PAM), polyamine, and chitosan, have high flocculation efficiency and h3 adsorption capacity. They can form large and dense flocs through bridging effects, improving sedimentation speed and solid-liquid separation effect. In practical applications, inorganic and organic coagulants are often used in combination to achieve better treatment results.

The selection and dosage of coagulants and flocculants are affected by many factors, such as water quality (pH, turbidity, pollutant concentration), treatment process, and temperature. For example, in water with high turbidity, a higher dosage of coagulants may be required; in acidic water, the pH needs to be adjusted first to ensure the hydrolysis of coagulants. In addition, the addition sequence of chemicals also affects the flocculation effect. Generally, coagulants are added first to complete the charge neutralization, and then flocculants are added to promote floc growth. With the development of water treatment technology, new types of coagulants and flocculants, such as composite coagulants and biological flocculants, are constantly emerging, which have the advantages of environmental friendliness and high efficiency, and will gradually replace traditional products in some fields.