The Coagulant Decision
Choosing between Polyaluminium Chloride (PAC) and Aluminum Sulfate (Alum) is one of the most common decisions water treatment operators face. Here is a practical comparison.
Cost Comparison
While PAC typically costs 30-50% more per kilogram than alum, the total treatment cost is often lower due to: 30-50% lower dosage requirements, reduced or eliminated pH adjustment chemicals, 20-40% less sludge disposal costs, and shorter settling time enabling higher throughput.
Performance Comparison
| Factor | PAC | Aluminum Sulfate |
|---|---|---|
| Effective pH range | 5.0 – 9.0 | 6.5 – 7.5 |
| Cold water performance | Excellent | Poor below 10C |
| Floc formation speed | Fast (2-5 min) | Moderate (5-15 min) |
| Residual aluminum | Low (0.01-0.05 mg/L) | Higher (0.05-0.15 mg/L) |
| Sludge volume | Lower | Higher |
When to Choose PAC
- Source water with high or variable turbidity
- Cold climate operations
- Plants with limited pH adjustment capability
- Strict aluminum residual limits in treated water
- High-throughput plants needing faster settling
When Alum May Still Be the Choice
- Very stable, low-turbidity source water
- Budget-constrained operations where chemical cost is primary
- Existing dosing systems optimized for alum
HydroChemix supplies PAC and related products. Contact us for a technical comparison specific to your source water.