How to Use Anionic PAM (Medium Molecular Weight) in Water Treatment

Overview

Anionic polyacrylamide (APAM) with molecular weight 12–16 million Da is the most versatile flocculant for water and wastewater treatment. It works by bridging flocculation — long polymer chains bridge between coagulated particles to form large, fast-settling flocs. Used after coagulant (PAC/PFS) addition.

Preparation & Dissolution

Critical: PAM dissolution requires patience.

1. Fill dissolving tank with clean water at 20–30°C
2. Start agitator at 100–200 rpm
3. Sprinkle PAM powder slowly into the vortex — DO NOT dump all at once (causes fisheyes)
4. Continue stirring for 60 minutes minimum — polymer must fully hydrate
5. Final solution concentration: 0.1% (1 g/L) — this is the standard working concentration
6. Prepared solution is stable for 48 hours; discard after that

Pro tip: Use a screw feeder or dry powder disperser for consistent addition. Manual sprinkling works for small batches (< 50L).

Dosing Guide

Application	Dose (as dry PAM)	Notes
After PAC in drinking water	0.2–1.0 ppm	Low dose to avoid polymer residual
After PAC/PFS in municipal WW	0.5–2.0 ppm	Most common application
After PFS in industrial WW	1.0–3.0 ppm	Higher for high-TSS wastewater
Mining tailings thickener	2.0–5.0 ppm	High MW may be better for very coarse particles
Sand/gravel wash water	0.5–1.5 ppm	Fast floc formation

Application Procedure

1. Add coagulant (PAC/PFS) first — flash mix 1 minute at high speed
2. Wait 1–2 minutes for coagulation reaction
3. Add 0.1% APAM solution at the slow-mix inlet
4. Slow mix at 30–50 rpm for 10–20 minutes — observe floc growth
5. Stop stirring — flocs should settle within 5–10 minutes in a jar test
6. Transfer to sedimentation basin
7. Do NOT add more PAM if flocs are small — check if coagulant dose is adequate first

Monitoring & Control

Parameter	Frequency	Target
Settled water turbidity	Every 30 min	< 5 NTU
Floc size	Visual	Pin-head to pea-size, dense
Settling velocity	Jar test	> 2 mm/s for good flocs
Polymer residual	Weekly (drinking)	< 0.5 mg/L (regulatory)

Common Mistakes

• Dumping powder into water: Creates insoluble lumps ("fisheyes") that waste product and clog pumps. Always sprinkle slowly.
• Insufficient dissolution time: Undissolved PAM gives poor floc quality. Full 60 minutes is non-negotiable.
• Using hot water (> 60°C): Heat degrades PAM polymer chains, reducing MW and effectiveness.
• Adding PAM before coagulant: PAM works by bridging already-coagulated particles. Without prior coagulation, PAM has nothing to bridge.
• Overdosing: Excess PAM can restabilize particles. Typical sweet spot is 0.5–2 ppm — more is NOT better.

Storage & Handling

• Shelf life: Dry powder — 24 months in sealed, cool, dry storage. Solution — use within 48 hours.
• Temperature: Store powder at 5–35°C, away from moisture. Solution should be used at 15–30°C.
• Container: Original bags on pallets. Keep off concrete floors (moisture absorption).
• Safety: Low toxicity but slippery when spilled. Acrylamide monomer content < 0.05% in commercial grades. Wear dust mask when handling powder.