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Polyaluminium Chloride (PAC) and Aluminium Sulphate (Alum) in high pH effluent treatment.
Introduction
When it comes to treating high pH industrial effluent, coagulant selection is critical for effective water clarification and regulatory compliance. Two of the most widely used coagulants in water and wastewater treatment are Polyaluminium Chloride (PAC) and Aluminium Sulphate (Alum). But which one performs better in high pH conditions? This article provides a clear, step-by-step comparison of PAC vs Aluminium Sulphate, with practical examples, expert recommendations, and answers to common questions.
Step 1: Understanding the Chemistry
What is PAC?
Polyaluminium Chloride (PAC) is a highly efficient, pre-hydrolyzed aluminium-based coagulant. It is available in liquid and powder forms and is used for enhanced coagulation and flocculation in water and wastewater treatment.
Key Features:
- Works across a broad pH range (5–9, and sometimes higher)
- Rapid floc formation and settling
- Lower sludge volume
What is Aluminium Sulphate (Alum)?
Aluminium Sulphate (commonly known as Alum) is a traditional coagulant used in water treatment. It is effective but has certain limitations at higher pH levels.
Key Features:
- Most effective at pH 5.5–7.5
- Produces more sludge compared to PAC
- Lower cost but requires precise pH control
Step 2: Coagulant Performance in High pH Effluent
PAC in High pH Effluent
- Effectiveness: PAC maintains high coagulation efficiency even as pH increases (up to 9 and sometimes higher).
- Chemical Demand: Less acid is needed to adjust pH before PAC dosing, reducing chemical costs.
- Turbidity & Colour Removal: Consistently high removal rates for turbidity and organic matter.
- Residual Aluminium: Lower residual aluminium levels compared to Alum.
Example:
A textile factory with effluent pH of 8.8 switched from Alum to PAC and observed a 30% reduction in chemical usage, better turbidity removal, and less sludge.
Aluminium Sulphate in High pH Effluent
- Effectiveness: Coagulation efficiency drops significantly above pH 7.5–8.5.
- Chemical Demand: Requires more acid dosing to bring pH into the optimal range, increasing operational costs.
- Turbidity & Colour Removal: Less effective at higher pH, leading to higher chemical consumption and possible compliance issues.
- Residual Aluminium: Higher risk of residual aluminium in treated water.
Example:
A municipal water plant using Alum at pH 8.7 had to add significant quantities of acid to maintain performance, resulting in higher operational costs and more sludge compared to PAC.
Step 3: Practical Application and Dosage
- PAC Dosage (High pH): 10–50 mg/L, depending on contaminant load and pH.
- Alum Dosage (High pH): Often higher than PAC, and requires more acid for pH adjustment.
Tip: Always jar-test both coagulants with your specific effluent to determine the most effective and economical dosage.
Step 4: Operational Advantages & Disadvantages
| Feature | PAC | Aluminium Sulphate (Alum) |
|---|---|---|
| Effective pH Range | 5–9+ | 5.5–7.5 (drops above 8) |
| Chemical Consumption | Lower | Higher |
| Sludge Volume | Lower | Higher |
| Residual Aluminium | Lower | Higher |
| Cost per kg | Higher than Alum | Lower than PAC |
| Overall Treatment Cost | Often lower due to efficiency | Higher at high pH due to acid use |
Step 5: Recommendations
- For high pH effluent (pH 8–9+), PAC is generally more effective, economical, and environmentally friendly than Alum.
- Alum may be suitable for neutral or slightly acidic effluent, but its performance drops at elevated pH.
- Always consult with a water treatment specialist and conduct site-specific testing for best results.
People Also Ask
Is PAC better than Alum for high pH water?
Yes, PAC is more efficient and requires less pH adjustment, making it superior for high pH effluent.
What is the main disadvantage of Aluminium Sulphate at high pH?
Alum’s coagulation efficiency drops sharply above pH 7.5–8, requiring extra acid and producing more sludge.
Can PAC and Alum be used together?
In some cases, a combination may be used for specific treatment goals, but PAC alone often suffices at high pH.
Does PAC leave less residual aluminium than Alum?
Yes, PAC tends to leave lower residual aluminium in treated water, reducing health and compliance risks.
FAQ
Q: What is the typical dose of PAC for high pH effluent?
A: PAC is usually dosed at 10–50 mg/L, but exact dosage should be determined through jar testing.
Q: Is PAC more expensive than Alum?
A: Per kg, PAC is pricier, but overall treatment costs are often lower because of its higher efficiency and reduced need for pH adjustment and sludge handling.
Q: How do I switch from Alum to PAC?
A: Consult your chemical supplier or water treatment expert. Start with jar testing, optimize dosage, and monitor effluent quality and sludge generation.
Q: Are there safety concerns with PAC or Alum use?
A: Both are safe when handled properly. Always follow manufacturer safety guidelines and provide adequate PPE for operators.
Conclusion
When comparing Polyaluminium Chloride (PAC) and Aluminium Sulphate (Alum) for high pH effluent treatment, PAC clearly outperforms Alum in terms of coagulation efficiency, cost-effectiveness, and operational simplicity. PAC’s broader pH range and lower chemical demand make it the smart choice for industries and facilities dealing with alkaline wastewater.
For best results, conduct pilot tests with your effluent and consult with experienced chemical suppliers or water treatment professionals.
Need help choosing the right coagulant for your high pH effluent? Contact Brand Chemical Supplies for expert advice, product samples, and competitive pricing.
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