PAC vs PFS: Which Coagulant for Your Wastewater?

Overview

PAC (Polyaluminum Chloride) and PFS (Poly Ferric Sulfate) are the two most widely used inorganic coagulants in water treatment. This guide helps you choose the right one.

Head-to-Head Comparison

Parameter	PAC 30%	PFS
Active content	≥ 30% Al₂O₃	≥ 19% Fe
Working pH range	5.0–9.0	4.0–11.0
pH depression	Minimal	Moderate
Cold water performance	Moderate	Excellent
Color removal	Good	Superior
COD removal	Moderate	Good
Sludge volume	Lower	Higher (denser flocs)
Settling speed	Fast	Very fast
Cost per kg	Lower	Slightly higher
Aluminum residual risk	Yes (monitor for drinking water)	No
Iron residual risk	No	Possible (yellow tint)

When to Use PAC

• Drinking water treatment — lower residual risk, well-characterized safety
• General municipal wastewater — cost-effective at scale
• Low-color wastewater — adequate performance at lower cost
• pH-sensitive systems — minimal pH impact

When to Use PFS

• Cold water (< 5°C) — PAC slows down in cold water, PFS does not
• High-color wastewater — superior color removal (textile, paper)
• Low-alkalinity water — works better than PAC without lime addition
• High COD effluent — better organic matter co-precipitation
• Heavy metal co-removal — iron hydroxide co-precipitates metals better

Combined Use

Some plants use PAC for primary coagulation + PFS for polishing, or switch seasonally (PAC in summer, PFS in winter when water is cold).

Cost Analysis

At typical dosing (30–80 ppm as product):

• PAC: $0.02–0.05/m³ treated water
• PFS: $0.03–0.06/m³ treated water
• PFS delivers better results per dollar in cold water and high-color applications

Recommendation

Start with PAC for general applications — it covers 70% of use cases at lower cost. Switch to PFS when you encounter cold water, high color, or need better COD removal.