Two of the most common questions we get from procurement teams comparing water-treatment quotes are:
"Why is one vendor quoting PAC and the other CPAM for what sounds like the same problem? And is either cheaper?"
They're not the same problem and they're not priced the same way. Here's the short version you can give your operations manager.
The 30-second answer
Poly Aluminium Chloride (PAC) is an inorganic coagulant. It's a salt — specifically a partially-hydrolysed aluminium chloride polymer. It works by neutralising the negative charge on colloidal particles so they can aggregate. You dose a lot of it (tens to hundreds of ppm), it's cheap per kilogram, and it raises the sludge volume.
Cationic Poly Acrylamide (CPAM) is an organic flocculant. It's a long, high-molecular-weight polymer with positively-charged side groups. It works by bridging — once PAC has neutralised the charges, CPAM's long chains physically hook multiple particles together into big, dense flocs you can settle or dewater. You dose a little of it (sub-ppm to single-digit ppm), it's expensive per kilogram but efficient per volume treated, and it dramatically reduces sludge volume.
They're not interchangeable — they run in sequence
In a well-designed coagulation-flocculation train, PAC comes first (rapid mix) and CPAM comes second (slow mix before settling or dewatering). The PAC does the chemistry; the CPAM does the physics. Substituting one for the other usually leaves performance on the table — you can get PAC-only to clarify, but your sludge volume is higher than it needs to be; you can get CPAM-only to flocculate, but only if your feedwater already has low surface charge, which is rare in real plants.
When to use which (or both)
- Drinking-water clarification (surface water): PAC does most of the work. CPAM is optional and only added if settling rates are limiting your clarifier throughput.
- Industrial effluent with heavy colloidal load (dyeing, paper, metal finishing): PAC + CPAM together. PAC dose comes first for charge neutralisation; CPAM polishes and densifies the flocs for downstream dewatering.
- Sludge dewatering (belt press, decanter centrifuge, filter press): CPAM almost exclusively. The sludge has already been coagulated upstream; CPAM's job here is purely bridging to get the dry-solids percentage up.
- Municipal sewage primary clarification: Typically PAC alone, unless clarifier hydraulics demand faster settling.
What to specify to your vendor
A vendor who can't tell you the right answer from your feedwater analysis isn't worth the phone call. When you request a quote for PAC or CPAM, include:
- Turbidity, SS, COD, pH, temperature, conductivity of the raw water (or the water at the point where chemistry enters)
- The downstream process (sand filter? RO? decanter? belt press?)
- Target output KPI (e.g., <1 NTU turbidity into RO; or 22% dry solids out of centrifuge)
- Current chemistry and dosing if replacing an existing programme
That lets us reply with a specified product grade (there are half a dozen PAC grades and a dozen CPAM variants), a dose range, and an expected outcome — instead of "here's a bag, good luck."
Typical cost structure for a Pakistani buyer
At today's USD parity, bulk PAC (32% Al₂O₃ solid, FCA Karachi) runs roughly a third the per-kg price of high-MW CPAM. But because CPAM is dosed at around a hundredth the rate of PAC, your per-m³-treated cost is usually similar or lower with CPAM — especially if the CPAM halves your sludge-disposal bill.
If you're evaluating a chemistry change, don't just compare product prices — compare treatment cost per m³, sludge volume, and downstream equipment load. That's the number that matters.
Need help with a specific feedwater or effluent profile? Send us the analysis and we'll come back with a specified dosing programme.