New Wastewater Treatment Advances for Polyaluminum Chloride Industry

When polyaluminum chloride (PAC), widely hailed as a "water treatment miracle" in industrial production, generates wastewater during its own manufacturing process that poses serious environmental concerns, how should we resolve this contradiction? As a highly efficient coagulant, PAC holds a prominent position in municipal water supply and industrial wastewater treatment. However, the high-concentration, high-salinity wastewater containing heavy metal residues from its production process can cause irreversible ecological damage to receiving waters if discharged without proper treatment. Therefore, establishing a scientific and efficient wastewater treatment system represents not only the baseline of corporate environmental responsibility but also a crucial component of achieving green industrial production.

PAC production wastewater primarily originates from the reaction process between bauxite/aluminum hydroxide and hydrochloric acid, as well as subsequent drying and crushing procedures. The wastewater exhibits significant complexity:

• Extreme pH fluctuations, typically strongly acidic
• High concentrations of aluminum ions and residual chloride ions
• Unreacted organic additives and trace heavy metals (chromium, arsenic, lead, etc.) from equipment cleaning and exhaust absorption processes

These pollutants demonstrate strong biotoxicity and can cause severe eutrophication and heavy metal accumulation if entering soil or groundwater systems.

To address PAC production wastewater characteristics, the industry has established a standardized treatment framework following the sequence: "pretreatment → chemical precipitation → advanced filtration → compliant discharge."

1. Pretreatment and Solid-Liquid Separation: Wastewater first passes through mechanical screens to intercept large particles, preventing pipeline blockages. Equalization tanks balance water volume while alkaline additives neutralize acidic substances.

2. Chemical Coagulation and Precipitation: This critical stage utilizes PAC's inherent adsorption and bridging effects on colloidal particles. Adding coagulant aids (e.g., polyacrylamide PAM) promotes aggregation of fine suspended solids into larger flocs. Subsequent sedimentation tanks enable gravity-based sludge separation, removing most heavy metal ions.

3. Advanced Filtration and Purification: Post-sedimentation supernatant undergoes multi-media filtration (quartz sand, activated carbon) to remove residual suspended solids and adsorb organic pollutants, ensuring turbidity compliance.

4. Disinfection and Compliant Discharge: Final disinfection using sodium hypochlorite or ultraviolet irradiation eliminates pathogenic microorganisms, guaranteeing effluent quality meets national wastewater discharge standards.

Despite process maturity, PAC wastewater treatment faces ongoing challenges under increasingly stringent environmental regulations. High-salinity wastewater desalination remains costly, while sludge treatment requires substantial resources for heavy metal stabilization.

The industry's future focus will shift toward "resource recovery and recycling" through membrane separation technologies (nanofiltration, reverse osmosis) to reclaim aluminum salts, achieving wastewater reduction and resource utilization. This transition from "end-of-pipe treatment" to "process control" represents the essential pathway for sustainable PAC industry development. Through refined management and advanced process integration, manufacturers can simultaneously eliminate environmental risks, enhance production efficiency, and create an industrial ecosystem balancing ecological and economic benefits.