PAC and PAM: A Proven Combination
In wastewater treatment, polyaluminum chloride (PAC) and polyacrylamide (PAM) are the most commonly paired chemicals. In simple terms: PAC does the gathering, PAM does the settling. PAC — an inorganic coagulant — destabilizes suspended particles to form micro-flocs. PAM — an organic polymer flocculant — then bridges those micro-flocs into larger, faster-settling aggregates.
Key Differences at a Glance
- Type: PAC is inorganic polymer / PAM is organic polymer
- Appearance: PAC is yellow to brown powder / PAM is white powder or granules
- Ionic Character: PAC is primarily cationic / PAM comes in anionic, cationic, and non-ionic forms
- Primary Function: PAC handles charge neutralization and coagulation / PAM handles adsorption bridging and flocculation
- Dosing Point: PAC at the coagulation tank inlet / PAM at the flocculation tank mid-section
- Typical Dosage: PAC: tens to hundreds of mg/L / PAM: only a few mg/L
The Correct Dosing Sequence
Add PAC first, then PAM — with a 30–60 second interval.
PAC first neutralizes the negative surface charges on colloidal particles, causing them to destabilize and form tiny micro-flocs. PAM’s long molecular chains then bridge these micro-flocs into large, visible flocs that settle rapidly. If the sequence is reversed, PAM coats the particle surfaces and blocks PAC from functioning — significantly reducing overall effectiveness.
Standard Dosing Procedure
- PAC Preparation: Dissolve at 5–10% concentration. Stir until uniform. Prepare fresh before each use
- PAM Preparation: Dissolve at 0.1–0.3% concentration. Stir slowly for 40–60 minutes to achieve full dissolution
- Dosing: Add PAC at the inlet pipe or coagulation tank entry; add PAM at the mid-point of the flocculation tank
- Mixing: Rapid mixing for the PAC stage (150–300 rpm); slow mixing for the PAM stage (30–60 rpm)
How to Determine Optimal Dosage
Jar testing is essential. Bench-scale testing quickly identifies the best ratio:
- Keep PAM dosage constant; increase PAC dosage stepwise — observe floc size and settling rate
- Fix the optimal PAC dosage; adjust PAM dosage incrementally
- Record supernatant turbidity, floc settling time, and sludge volume for each run
Common Issues and Solutions
- Fine, broken flocs that won\’t settle: Insufficient PAM dosage or mixing too fast (broken flocs) — reduce mixer speed
- Milky, hazy supernatant: PAC overdose — reduce PAC dosage accordingly
- Floating flocs: PAM overdose causing gas bubbles to attach — reduce PAM dosage
- High effluent viscosity: Excess unreacted PAM — check dosage amount and dissolution quality
This article is for informational purposes. Process parameters should be determined through jar testing based on actual water quality conditions.