In the sewage treatment of papermaking, steel, metallurgy, mineral processing, chemical, electroplating, slaughter, urban sewage and other industries, it is often necessary to add polyaluminum chloride and polyacrylamide to accelerate the sedimentation rate of pollutants in the water in the process of flocculation and precipitation. When adding specific agents, polyaluminum chloride is added first, and then polyacrylamide is added. Why? We need to know the functions of PAC and PAM first.
The Role of Polyaluminium Chloride
- The aqueous solution of polyaluminum chloride is acidic, with a pH between 3.5-5.0, which can adjust the pH of the water quality.
- The applicable water pH range of polyaluminum chloride is between 3-12, which is wider than that of polyacrylamide.
- After polyaluminum chloride comes into contact with sewage, it will first form flocculent small particle groups.
- Polyaluminum chloride is a coagulant, whichcan play a role in coagulation.
- PAChas a certain demulsification ability.
- When PACis used alone, floccules will form in the water, but these flocs are not easy to settle, the water quality is turbid after treatment, and the effect of rapid flocculation and sedimentation cannot be achieved.
The Role of Polyacrylamide
- When using polyacrylamide, the pH range of water quality is between 6-9.
- When polyacrylamide is used alone, the added amount is large and the effect is poor. It is necessary to adjust the PH value with a coagulant first.
Therefore, by adding polyaluminum chloride first, the pH of the water can be adjusted to 6-9, which is more suitable for the use of polyacrylamide. At the same time, polyaluminum chloride can also play a role in assisting coagulation, helping polyacrylamide to accelerate the sedimentation, making the water clear and sludge sinking. This is why need to add PAC first and then PAM in sewage treatment process.