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.
Related Water Treatment Resources
- PAC and PAM dosing guide: preparation, dosage, and jar testing
- Heavy metal capture agent for electroplating, mining, and chemical wastewater
- PAC vs sulfato de aluminio: dosis, pH, lodos y costos
FAQ: PAC and PAM in Wastewater Treatment
What is the main difference between PAC and PAM?
PAC is an inorganic coagulant used mainly for charge neutralization and micro-floc formation. PAM is an organic polymer flocculant used to bridge particles into larger flocs for settling, flotation, or sludge dewatering.
Can PAC and PAM remove COD?
PAC and PAM can help reduce particulate COD, color, and suspended solids when the COD is associated with colloids or particles. Dissolved COD may require additional oxidation, biological treatment, adsorption, or specialty chemicals.
Which PAM type should be used with PAC?
Anionic, cationic, or non-ionic PAM may be selected depending on wastewater source, sludge charge, and treatment goal. Jar testing is recommended before confirming the PAM grade.
Why does overdosing PAC or PAM cause poor results?
PAC overdose may cause charge reversal and cloudy supernatant. PAM overdose can create sticky flocs, floating sludge, high viscosity, or poor filtration performance.
What information is needed for a PAC/PAM recommendation?
Useful details include wastewater industry, pH, turbidity, COD, suspended solids, current treatment process, daily flow, sludge handling method, and target discharge requirement.