DOSING GUIDE
How Much Polyaluminium Chloride to Dose?
The honest answer to "how much PAC should I dose" is: somewhere between 5 and 200 mg/L, and your water decides where in that range you sit. This guide gives the typical ranges by application, the jar-test routine that pins down your number, and the conversion rules between solid and liquid grades.
Typical PAC dose ranges by application
The table below lists typical working ranges for commercial PAC product (not pure Al2O3). They are starting points for a jar test, not final answers - raw water varies enormously even within one industry.
| Application | Typical dose (mg/L, as product) |
|---|---|
| Surface water clarification (drinking water plants) | 5 – 30 |
| Municipal wastewater, chemically assisted primary settling | 30 – 80 |
| Industrial wastewater physico-chemical treatment | 50 – 200 |
| Paper / pulp process water | 20 – 60 |
| Coal washing and mineral processing water | 30 – 100 |
Dose depends on five things
Turbidity and suspended solids set the baseline - more solids, more charge demand. Temperature slows everything down: below 10 °C hydrolysis is sluggish and flocs form later. Alkalinity buffers the pH drop that PAC causes; soft, low-alkalinity water needs careful pH control. Organic matter (colour, humics) consumes coagulant without producing floc. Finally, your process goal matters - polishing for a 1 NTU outlet needs a different dose than bulk solids removal for a discharge permit.
The jar test: how to find your actual dose
A jar test takes twenty minutes and saves months of guessing. Fill six beakers with your raw water. Dose 0, 10, 20, 30, 40 and 50 mg/L PAC (scale the range to your application). Flash mix at 200-300 rpm for 30 seconds, then slow stir at 40-60 rpm for 15 minutes, then settle for 20 minutes.
Read two numbers, not one: residual turbidity of the supernatant, and the point where flocs first form quickly. The economic dose is usually just above the first dose where turbidity stops improving - going beyond it buys sludge volume, not clarity. For drinking water applications, also check residual aluminium in the supernatant.
The pH window
PAC works across a wider pH band than alum, roughly 5.5 to 8.5, which is one of its main advantages. But the sweet spot for charge neutralisation is pH 6.5 - 7.5. Below 5.5 the aluminium stays soluble and flocs are poor; above 8.5 aluminate re-forms and you can see residual aluminium rise. Check alkalinity before your trial: if your water sits below 50 mg/L as CaCO3, add alkalinity or expect the pH to drift down at higher doses.
Liquid vs solid: the conversion rule
Our solid PAC carries Al2O3 28% (industrial, GB/T 22627-2022) or 29% (drinking water, GB 15892-2020). Liquid PAC typically runs at 10% Al2O3 drinking-water grade. The conversion is simple arithmetic: one kilogram of solid 28% equals about 2.8 kilograms of liquid 10%. When you compare prices between suppliers, always convert to a per-kilogram-of-Al2O3 basis first - a cheaper per-tonne price on liquid is often more expensive per unit of active coagulant.
See our polyaluminium chloride specification page for the full grade list.
Frequently asked questions
What happens if I overdose PAC?
Two things, both expensive. First, residual aluminium in the outlet rises, which matters for drinking water (limit 0.2 mg/L in China GB 5749-2022). Second, restabilisation: over-dosed colloids can flip charge and go back into suspension, so turbidity gets worse instead of better. The jar test protects you from both.
Can I dose PAC and PAM at the same injection point?
No. PAC needs 30-60 seconds of rapid mixing to neutralise charges before PAM is added. If they meet in the same chemical feed line or the same injection point, PAM bridges particles before neutralisation is complete and flocs come out small and weak. Space the injection points at least one mixing stage apart.
How fast should I expect flocs to appear?
With a correctly matched dose, pin flocs appear within 30-60 seconds of mixing at pH near neutral. If nothing shows after two minutes of slow stirring, the dose or the pH is off - re-check both before blaming the product.
Do you supply liquid PAC for export?
Yes, in IBC totes, but note the economics: liquid is about 72% water. Most export customers choose 25 kg bags of solid powder or 1000 kg jumbo bags and dissolve on site - freight per unit of Al2O3 is far lower. Liquid makes sense mainly for short-haul customers.