BASICS
PAC vs PAM: Which One Fixes Which Problem?
Buyers mix these two up constantly, and suppliers rarely stop to explain. PAC and PAM are not competitors - they do two different jobs in the same train, and most plants that run well use both. Here is the difference in plain language.
Two different mechanisms
PAC (polyaluminium chloride) is an inorganic coagulant. Its aluminium species carry positive charges that neutralise the negative surface charge keeping colloids apart. Once neutralised, particles collide and clump into micro-flocs. It works fast, in seconds, and needs violent mixing.
PAM (polyacrylamide) is an organic flocculant - a very long synthetic polymer. Its chains adsorb onto many particles at once and bridge them into large, strong flocs. It works slower than PAC, in minutes, and needs gentle mixing: aggressive stirring tears the bridges apart.
Side by side
| PAC (Coag Aqua) | PAM (Floc Aqua) | |
|---|---|---|
| Category | Inorganic coagulant | Organic flocculant |
| Mechanism | Charge neutralisation | Bridging |
| Typical dose | 10 – 200 mg/L | 0.1 – 5 mg/L |
| Mixing | Fast, vigorous (30 – 60 s) | Slow, gentle (minutes) |
| Forms | Powder, liquid | Powder, emulsion, bead |
| Grades we make | 28% industrial / 29% drinking water | Anionic, cationic, non-ionic |
| What it costs per tonne | Low | Higher (but dose is tiny) |
Why most plants use both
PAC alone produces small, loose flocs that settle but leave turbidity behind or need long settling times. PAM alone cannot neutralise charges, so on stable colloids it does almost nothing. Together: PAC destabilises the colloid in the rapid-mix chamber, then PAM is injected 30-60 seconds downstream, after neutralisation, and gathers everything into large flocs your clarifier can actually catch. Dose ratios are typically 20-50 mg/L PAC with 0.2-1 mg/L PAM - a hundred-to-one weight difference, which is why a small PAM order lasts a long time.
Diagnosis: which product is your problem?
- Flocs form but stay small and settle slowly - you need PAM (or a better PAM dose point), not more PAC.
- Turbidity barely drops no matter how much PAC you dose - check pH and alkalinity first; if the colloid is never destabilised, no flocculant will save it.
- Outlet turbidity fine but sludge watery and voluminous - add a small PAM dose to compact the flocs and cut sludge volume.
- Sludge dewatering poor on your press or centrifuge - that is a PAM job entirely (cationic, see our anionic vs cationic guide).
Ordering both from one plant
Because the two stages interact, ordering them from one producer has a practical benefit: the jar test that quotes your PAC also determines the PAM grade and dose point, so the combination arrives already matched. Send your water analysis through the quotation page and we will quote both together.
Frequently asked questions
Can I replace PAC with PAM?
No - they are not interchangeable. PAM cannot neutralise colloid charges, so on its own it fails on most raw waters. Conversely, PAC alone leaves small flocs that settle slowly. If your budget allows only one product today, start with PAC for clarification and add PAM when sludge handling or settling speed becomes the bottleneck.
What happens if PAC and PAM are dosed at the same point?
They meet before neutralisation is complete and form a gel-like precipitate - you lose both products and can foul the feed line. Keep at least one mixing stage (30-60 seconds) between the injection points.
Is PAC or PAM more dangerous to handle?
Both are low-hazard industrial chemicals, but differently: PAC is acidic and corrosive to skin and equipment, so gloves and goggles plus corrosion-resistant dosing hardware are needed. PAM powder is a dust and slip hazard; wet PAM is extremely slippery on floors. Neither is classified as dangerous goods for transport.