Poly Aluminum Chloride (PAC) is one of the most widely used coagulants in industrial water treatment. Thanks to its strong charge neutralization and adsorption capacity, PAC is highly effective in removing suspended solids, heavy metals, color, COD, and fluoride from various types of industrial wastewater.
In this article, we explain the main industrial applications of PAC, typical wastewater characteristics, treatment processes, dosage ranges, and treatment results.
1. Wastewater Treatment in the Steel Industry
Wastewater Characteristics
Steel industry wastewater usually contains:
- High suspended solids (iron scraps, ore powder)
- Heavy metal ions (zinc, lead, etc.)
- Colloidal substances
Treatment Process
PAC is added at a dosage of 0.5–1.5‰.
- PAC rapidly forms flocs through adsorption and bridging
- Combined with sedimentation tanks for solid–liquid separation
- Suspended solids are efficiently removed
Treatment Effect
- Effluent turbidity reduced by more than 85%
- Heavy metal ion removal rate exceeds 70%
- Treated water meets industrial discharge standards
2. Decolorization of Dyeing Wastewater
Wastewater Characteristics
Dyeing wastewater is known for:
- High color intensity (dye residues)
- High COD
- Large pH fluctuations
Treatment Process
PAC is used together with pH adjusters at a dosage of 0.8–1.2‰.
- PAC forms Al(OH)₃ colloids
- Dye molecules are adsorbed and destabilized
- Air flotation is applied to enhance separation
Treatment Effect
- Color removal rate reaches up to 90%
- Significant COD reduction
- Improved clarity for downstream treatment
3. Pretreatment of Polyester Chemical Wastewater
Wastewater Characteristics
Polyester chemical wastewater features:
- Extremely high COD (up to 30,000 mg/L)
- Macromolecular organics such as:
- Terephthalic acid
- Ethylene glycol esters
Treatment Process
PAC is applied at 0.3–0.5‰, combined with polyacrylamide (PAM).
- PAC neutralizes colloidal charges
- PAM strengthens floc formation
- Large organic particles are removed in pretreatment
Treatment Effect
- Initial COD reduction of about 40%
- Creates favorable conditions for:
- Iron–carbon micro-electrolysis
- UASB anaerobic treatment
4. Treatment of Daily Chemical Wastewater
Wastewater Characteristics
Daily chemical wastewater contains:
- High levels of surfactants
- Oils and emulsified substances
- Strong water quality fluctuations
Treatment Process
PAC dosage: 0.2–0.4‰
- Coagulation and sedimentation remove suspended solids
- Organic load is reduced before biological treatment
Treatment Effect
- COD reduced from 11,000 mg/L to 2,500 mg/L
- Significantly lowers the burden on biological systems
- Improves overall treatment stability
5. Purification of Glass Processing Wastewater
Wastewater Characteristics
Glass processing wastewater is typically:
- Strongly alkaline (pH > 10)
- Rich in fine glass grinding particles
- Poorly biodegradable
Treatment Process
Polymeric aluminum ferric chloride (PAFC) is used.
- Neutralizes alkalinity
- Promotes coagulation of fine particles
- Enhances solid–liquid separation
Treatment Effect
- Suspended solids removal rate exceeds 90%
- Effluent turbidity ≤ 5 NTU
- Ensures stable operation of downstream ultrafiltration systems
6. Treatment of High-Fluoride Industrial Wastewater
Wastewater Characteristics
Common in:
- Semiconductor manufacturing
- Etching and surface treatment industries
Fluoride concentration often exceeds 10 mg/L.
Treatment Process
PAC reacts with fluoride ions:
- Al³⁺ reacts with F⁻ to form AlF₃ precipitate
- PAC dosage adjusted based on fluoride concentration
Treatment Effect
- Fluoride reduced from 14.6 mg/L to 0.4–1.0 mg/L
- Effluent meets drinking water standards
- Safe for discharge or reuse
Conclusion
Poly Aluminum Chloride (PAC) is a highly versatile and cost-effective industrial water treatment coagulant. It is widely used in steel, dyeing, chemical, glass, and semiconductor industries to remove suspended solids, heavy metals, color, COD, and fluoride.
By selecting the correct dosage and combining PAC with suitable processes such as sedimentation, air flotation, or PAM-assisted flocculation, industrial wastewater can be treated efficiently and reliably. PAC plays a critical role in helping industries meet discharge standards while reducing operating costs.
