Introduction

Polyaluminium Chloride (PAC for short), as an efficient and economical inorganic high-molecular flocculant, has played a revolutionary role in the field of water treatment since its introduction in the 1960s. Compared with traditional aluminum salts, PAC, with its unique chemical structure and excellent performance, has demonstrated significant advantages in multiple fields such as drinking water treatment, sewage treatment, and industrial wastewater treatment, and has become an indispensable and important component of modern water treatment technology.

The chemical properties and advantages of PAC

PAC is a hydrolysis product between AlCl₃ and Al(OH)₃, and its general chemical formula is [Al₂(OH)ₙCl₆ ₙ ₙ]ₘ, where n is 1-5 and m≤10. This special structure endows PAC with many excellent characteristics:

High charge density: The PAC molecule contains a large number of highly charged polynuclear hydroxyl complexes, which can more effectively neutralize the surface charge of colloidal particles.

Stable polymerization form: PAC exists in a pre-polymerized form and does not undergo the complex transformation process from monomer to polymer like traditional aluminum salts during hydrolysis.

A wide pH adaptability range: The optimal pH range for traditional aluminum salts is 6.0-7.5, while PAC can maintain good flocculation effect within the range of 5.0-9.0.

Low-temperature adaptability: It can still maintain a high flocculation efficiency in low-temperature and low-turbidity water bodies, solving the problem of the decline in treatment effect of traditional aluminum salts in winter.

The application of PAC in Drinking Water Treatment

The contribution of PAC in drinking water treatment is mainly reflected in the following aspects:

Outstanding turbidity removal effect: Research shows that to achieve the same effluent turbidity standard, the dosage of PAC can be reduced by 30%-50% compared with traditional aluminum sulfate, the formed flocs are dense, and the sedimentation speed is 20%-30% faster.

High removal rate of organic pollutants: PAC has a remarkable removal effect on organic matter in water, especially dissolved organic carbon (DOC), and its removal rate of trihalomethane precursors (THMFP) is 15%-25% higher than that of traditional aluminum salts.

Excellent control of residual aluminum: After traditional aluminum salt treatment, the concentration of residual aluminum in water is usually between 0.2 and 0.5mg/L, while after PAC treatment, it can be controlled below 0.1mg/L, significantly reducing the potential risk of aluminum to human health.

Strong ability to deal with sudden pollution: When treating sudden high-turbidity raw water, PAC demonstrates rapid response and stable effluent quality, ensuring water supply safety.

Breakthroughs of PAC in wastewater treatment

PAC also demonstrates unique value in the field of sewage treatment:

Enhanced phosphorus removal effect: The highly charged Al₁₃ species in PAC can form stable precipitates with phosphate, and the total phosphorus removal rate can reach over 90%, meeting increasingly strict emission standards.

Reduced sludge production: Compared with traditional aluminum salts, the volume of sludge produced by using PAC is reduced by 20% to 30%, lowering the cost of sludge treatment and disposal.

Heavy metal co-precipitation: PAC can effectively capture heavy metal ions such as Cd, Pb, and Cu in wastewater and achieve deep removal through co-precipitation.

Excellent color removal: For colored wastewater such as printing and dyeing wastewater, the decolorization rate of PAC can reach 85%-95%, which is significantly better than that of traditional coagulants.

The special contribution of PAC in industrial wastewater treatment

In response to the characteristics of various industrial wastewater, PAC has demonstrated targeted treatment effects:

Papermaking wastewater: Effectively remove colloidal substances and anionic waste in the wastewater, and increase the COD removal rate by 30% to 40%.

Food processing wastewater: It has a good removal effect on proteins, oils and other substances in high-concentration organic wastewater, and does not cause secondary pollution.

Petrochemical wastewater: It can effectively demulsify and remove emulsified oil substances, with an oil removal rate of over 95%.

Pharmaceutical wastewater: For wastewater containing refractory organic matter, the combined use of PAC and biochemical processes can significantly enhance the overall treatment efficiency.

The environmentally friendly features of PAC

The application of PAC in water treatment also demonstrates significant environmental benefits:

Small pH impact: The pH of the water body changes little after use, reducing the consumption of chemicals for subsequent neutralization and regulation.

Low corrosiveness: Compared with traditional aluminum salts, PAC has significantly reduced corrosiveness to equipment, thereby extending the service life of treatment facilities.

Transportation and storage safety: Liquid PAC has good stability and is not prone to precipitation, while solid PAC has low hygroscopicity, making it convenient for transportation and storage.

Low comprehensive cost: Although the unit price is relatively high, considering multiple factors such as the dosage and sludge treatment, the overall treatment cost can be reduced by 15% to 25%.

Technological innovation and development trends

PAC technology is still constantly innovating and developing:

Composite PAC: The composite PAC product developed by introducing elements such as iron and silicon has further expanded its application scope and treatment effect.

High-purity and high-alkalization PAC: High-quality PAC produced by a special process, with Al₁₃ content reaching over 70%, offers even more outstanding treatment effects.

Application of nanotechnology: The research on nanoscale PAC provides new ideas for the advanced treatment of slightly polluted water bodies.

Intelligent dosing system: The PAC intelligent dosing technology based on online water quality monitoring has achieved precise dosing and optimized control.

Conclusion

As a major innovation in water treatment technology, PAC has been widely applied worldwide due to its characteristics of high efficiency, economy and environmental friendliness. It not only enhances the level of water quality safety guarantee and reduces treatment costs, but also promotes technological progress throughout the water treatment industry. With increasingly strict environmental protection requirements and the intensification of water shortage problems, PAC and its derivatives will continue to play a key role in the field of water treatment, making greater contributions to the improvement of human water environment and sustainable development. In the future, further innovations in PAC technology will be combined with the demands for intelligent and precise water treatment, ushering in a new era of water treatment technology.