Common Types of Sewage Flocculants and Their Usage Conditions

flocculants have always played a crucial role in municipal wastewater treatment. Looking back at the development history of flocculants in recent years, the types of flocculants have continued to increase. In addition to the leading sales of polyacrylamide flocculants, some flocculants such as aluminum salts and iron salts are also hot-selling in the market. Today, we will list some common categories of sewage flocculants and their usage conditions.

Organic polymer flocculant powder

Organic polymer flocculant powder contains polyacrylamide (PAM) and activated silica. PAM is a water-soluble polymer, insoluble in most organic solvents and primarily used for bridging. Its adsorption effect is stable, and the effective pH range is 7–14. It is generally used in conjunction with inorganic flocculants. Excessive dosages can lead to reverse solubility. Cationic polyacrylamide flocculants are used for activated sludge, while anionic polyacrylamide flocculants are used for physicochemical sludge. Non-ionic polyacrylamide flocculants are not suitable for both anionic and cationic effects. Activated silica is primarily used for bridging in low-temperature and low-turbidity water. It should be added after mixing and coagulating, and the preparation process is relatively complicated with suitable acidity and activation time.

Aluminum salt flocculant powder

The common aluminum salt flocculants include aluminum sulfate and alum. The principle is to compress the double layer, neutralize, and reduce the surface potential of colloids, emulsified oils, and hydrophilic organic substances. The coagulation effect is greatly affected by pH. The pH value should be between 4 and 7 for breaking emulsions and removing organic substances in water. For removing suspended solids in water, the pH value should be between 6 and 8. For water with high SS, the pH value should be between 6.5 and 8, and is applicable at 20–40℃.

Iron salt flocculant powder

The common iron salt flocculant powders include ferric chloride and ferrous sulfate. The principle is the same as aluminum salts. The usage is not affected by temperature, and the coagulation is dense with good sedimentation effect. The dosage is less than that of aluminum sulfate. It is corrosive to metals, concrete, and plastic. Ferrous ions need to be oxidized into trivalent iron, and chlorate oxidation is required when the pH is lower. The applicable pH range should be between 7 and 8.5. Fe2+ is stable within the range of 8.1–9.6. The coagulation occurs quickly, is stable, and sedimentation time is short.

As urban sewage becomes more complex, higher performance reagents are needed for sewage sludge dewatering. In this case, simple cationic flocculants are no longer applicable, and many tests and feedback have shown that amphoteric flocculants have a good effect.