Search for “polyamine water treatment” and you will mostly find product pages that describe polyamine as a chemical: CAS 42751-79-1, cationic polyelectrolyte, 50% solids, viscosity by grade. None of that answers the question a plant engineer actually has, which is where in the treatment train do I dose it, at what point relative to the coagulant and the flocculant, and how do I know when I have put in too much.
This page is about the program, not the product. It covers what polyamine does in a water treatment train, how it is sequenced with inorganic coagulants and with polyacrylamide, how the dose is set and checked, and the failure modes that look like a bad batch but are actually a bad dosing order.
For the chemical specification, the seven commercial grades and jar testing, see our polyamine technical guide; the current specification is on the polyamine product page.
What polyamine actually does in a treatment train
Polyamine is a low molecular weight, high charge density cationic polymer – typically an epichlorohydrin-dimethylamine condensate (EPI-DMA). That combination of properties places it in a specific job in the train:
| Property | Polyamine | Why it matters |
|---|---|---|
| Molecular weight | Low (typically tens of thousands) | Too short to bridge between particles over any distance – it cannot build a large floc on its own |
| Charge density | High, cationic | Very effective at neutralising the negative surface charge on colloids, which is the step that makes particles able to approach each other at all |
| Resulting action | Charge neutralisation and micro-floc formation | Produces small, dense flocs – fast settling but small, and easily broken by shear |
This is the single most useful thing to understand about the product: polyamine is a coagulant, not a flocculant. It does the charge work. Building the large, shear-resistant floc is a different polymer’s job.
The distinction has a direct commercial consequence. A plant that buys polyamine expecting flocculant performance will over-dose it, get re-stabilisation, and conclude the material is poor. A plant that doses it as a coagulant ahead of a flocculant gets a shorter settling time with less total polymer.
The three-stage sequence, and why the order is not optional
Most clarification trains that use polyamine run in three stages. The order matters because each stage changes the surface chemistry the next stage sees.
| Stage | Typical reagent | Job | If you get it wrong |
|---|---|---|---|
| 1 – Destabilisation | Inorganic coagulant: PAC, aluminium sulphate, ferric chloride | Collapses the double layer and sweeps particles into micro-flocs; also consumes alkalinity and shifts pH | Skip it and the polyamine has to neutralise all the charge itself, at a much higher dose |
| 2 – Charge finishing | Polyamine | Mops up the residual negative charge and the fine colloidal fraction the inorganic coagulant missed; forms dense micro-flocs | Dose it before the inorganic and it is consumed by the bulk turbidity with nothing left for the fines |
| 3 – Bridging | Anionic or weakly cationic PAM (high molecular weight) | Bridges micro-flocs into large, fast-settling, shear-resistant flocs | Dose PAM first and the polymer bridges particles that are still charge-stabilised, producing loose flocs that break in the pipe |
Two rules follow, and both are routinely broken:
- Never add polyamine before the inorganic coagulant. Cationic polymer added to raw, highly turbid water is consumed preferentially by the bulk of the suspended solids. The dose goes up, the result goes down.
- Never add PAM before polyamine if fines are the problem. PAM cannot bridge particles that are still electrostatically repelling each other. The floc looks large in the jar and disintegrates in the clarifier inlet.
Where the sequence is right, the polyamine dose is usually small relative to the inorganic coagulant and the PAM. Where it is wrong, the polyamine dose creeps up until it becomes the largest polymer cost on site – and still underperforms.
How much polyamine: the two orders of magnitude
Doses are quoted in two completely different bases, and confusing them is the second most common error after sequencing.
| Application | Dose basis | Order of magnitude | Note |
|---|---|---|---|
| Clarification of surface, process or potable water | mg/L (ppm) of product in the water | Single digits to low tens | Small because the inorganic coagulant has already done the bulk of the work |
| Sludge dewatering | kg of product per tonne of dry solids | Two orders of magnitude higher than clarification | Not comparable with the clarification figure at all – a plant comparing the two numbers will think one of them is wrong |
Neither number can be quoted as a design value without a jar test on the actual water, because both depend on turbidity, charge demand, pH, alkalinity and the upstream coagulant dose. What the orders of magnitude are useful for is a sanity check: if a clarification dose is being discussed in hundreds of ppm, the sequencing is almost certainly wrong, and adding more polymer will not fix it.
The failure mode that looks like a bad batch: overdosing
Cationic polymers re-stabilise colloids when overdosed. The mechanism is charge reversal: past the point of neutralisation the particles become positively charged, repel each other again, and the water gets worse as dose increases. In a jar test this shows as a dose-response curve that improves, peaks, and then degrades – and in a plant it shows as an operator adding more polymer to fix turbidity that the extra polymer is causing.
Three practical consequences:
- Deliberately find the overdose point in the jar test and record it. Operators need to know where the cliff is before they meet it at 3 a.m.
- Watch for turbidity that falls and then rises with dose. That signature is charge reversal, not contamination and not a bad batch.
- Do not “trim” with more polyamine. If the water quality changes and turbidity rises, the answer is usually to re-run the jar test and rebalance the three stages, not to increase stage 2.
Choosing the grade: A to G in program terms
The seven grades differ in viscosity and charge density, and the choice follows from what the plant needs the polymer to do. Our technical guide carries the full table; in program terms:
| If the plant needs | Grade family | Because |
|---|---|---|
| Pure charge neutralisation of colour and anionic trash | Highest charge density, lowest viscosity (A) | Maximum charge per kilogram, and low viscosity for easy make-down at low dose |
| Potable or industrial clarification with fine turbidity | Very high charge density (B) | Balances neutralisation with a little more bridging |
| Mixed wastewater load, some bridging wanted | Medium charge density, higher viscosity (D) | Trades charge for chain length, which suits water that is not purely colloidal |
| Faster settling and a larger floc without a separate flocculant | Highest viscosity (E) | Longer chains give some bridging, at the cost of charge density |
| Lower freight cost or a dosing pump that cannot handle 50% solids | 40% solids versions of C and D (F, G) | Same duty at lower active content – the chemistry is unchanged, the logistics differ |
A caution that belongs in every purchasing discussion: solid content is not active charge. A 50% product with low charge density can underperform a 40% product with high charge density, and the price per tonne will make the worse product look cheaper. Compare on cost per unit of charge demand removed, measured in a jar test, not on price per wet tonne.
Where the program differs: four settings
Potable and process water clarification
The simplest train: inorganic coagulant, polyamine for charge finishing, then either settling or filtration. The constraint is the residual polymer and monomer content in the finished water, so the dose is kept as low as the jar test allows, and food-contact or potable approvals are checked against the destination market’s rules rather than assumed from a generic certificate.
Municipal and industrial wastewater, and sludge dewatering
Here polyamine is often used as the primary conditioner ahead of a dewatering device, in combination with a high molecular weight PAM. The dose basis switches to kilograms per tonne of dry solids, the shear environment of the dewatering machine becomes the deciding factor, and the pair is tuned together: polyamine for charge, PAM for the floc that survives the belt press or centrifuge.
Papermaking wet end
In papermaking the same chemistry is sold as a fixative or anionic trash catcher: high charge density polyamine neutralises the dissolved and colloidal anionic material circulating in the white water before it can interfere with the retention aid. The dosing point is the machine chest or the fan pump, and the control variable is charge demand measured by streaming current or colloid titration – not turbidity. Our note on polyamine in papermaking covers that side in detail.
Oilfield produced water
In produced water treatment the target is often emulsified oil rather than suspended clay, and polyamine acts as a reverse demulsifier: it neutralises the charge on the oil droplets and lets them coalesce. The train differs from municipal clarification – there is usually no inorganic coagulant, the water is warm and saline, and the polyamine is judged on oil-in-water after separation rather than on turbidity.
Setting the dose: a working sequence
- Measure the charge demand of the water with colloid titration or streaming current. Without this number every dose decision is a guess.
- Fix stage 1 first. Optimise the inorganic coagulant dose for turbidity and pH before touching polyamine. Changing two stages at once produces results that cannot be attributed.
- Screen three grades – one low, one medium, one high viscosity – across a dose series with mixing held constant. Do not screen all seven.
- Judge on settled turbidity, floc size and settling rate together. A dense, fast-settling floc often beats a clearer but slow one on plant throughput.
- Find the overdose point and record it. Then set the operating dose at roughly two-thirds of it so there is headroom for a turbidity excursion.
- Then tune stage 3. Only after stages 1 and 2 are stable does PAM optimisation mean anything.
- Hold the make-down dilution constant. Polyamine is usually dosed as a dilute working solution, and a change of dilution changes the mixing energy at the injection point – which changes performance as much as a dose change.
Diagnosing a train that has stopped working
| Symptom | Most likely cause | Action |
|---|---|---|
| Turbidity rises as polyamine dose rises | Charge reversal from over-dosing | Cut the dose, re-run the jar test, find the peak |
| Floc forms in the jar, breaks in the plant | PAM stage insufficient, or shear at the transfer point | Increase or re-select PAM; check pump and valve shear, not polyamine |
| Polyamine consumption climbing with no quality gain | Polyamine being consumed by bulk turbidity because it is dosed before the coagulant | Move the injection point downstream of stage 1 |
| Good jar result, poor plant result | Mixing energy or dilution different in the plant | Match rapid-mix intensity and make-down concentration to the jar test |
| Sudden change with the same dose and same water | Raw water change (rain, algae, seasonal turbidity) or a coagulant supply change | Re-measure charge demand before changing polymer |
Supply, packaging and what to ask for
Polyamine is supplied as an aqueous solution, typically 50% or 40% solids, in drums, IBCs or bulk. Three practical points:
- Viscosity grades are not interchangeable in a dosing system. A high-viscosity grade may need a different pump and a more dilute working solution; confirm the pump curve before switching grades mid-contract.
- Ask for viscosity with the measurement conditions (spindle and speed). A figure without them cannot be compared across suppliers.
- Check the pH window per lot. The products are acidic to neutral and the plant may adjust, but a batch at the acid end and one at the neutral end behave differently in a buffered system.
For the clarified comparison of polyamine against the other organic flocculants, see polyamine versus PAM and PolyDADMAC and the flocculant selection chart. The polyacrylamide side of the train is covered in our PAM guide, and the alternative cationic coagulant in the PolyDADMAC guide.
FAQ
Is polyamine a coagulant or a flocculant?
A coagulant, in practice. It is a low molecular weight, high charge density polymer, so it neutralises charge and forms micro-flocs but cannot bridge over distance. The large floc comes from a high molecular weight PAM in the next stage.
Can polyamine replace PAM?
No. They do different jobs. Replacing PAM with polyamine gives small flocs that settle slowly and break under shear; replacing polyamine with PAM leaves the charge unneutralised and the floc loose.
What dose of polyamine do I need for water clarification?
It depends on the charge demand of the water and on how much of the work the inorganic coagulant is doing. In clarification it is normally a small fraction of the total chemical cost; if the required polyamine dose approaches the coagulant dose, the sequencing is usually wrong. Establish the number by jar test on your water.
Why does my water get cloudier when I add more polyamine?
Charge reversal. Past the neutralisation point, cationic polymer makes the particles positively charged and they repel each other again. Reduce the dose and re-run the jar test to find the peak.
Should polyamine be dosed before or after PAC?
After. The inorganic coagulant destabilises the bulk of the turbidity; polyamine then finishes the charge and captures the fines. Dosing polyamine first wastes it on the bulk solids.
Does higher solid content mean a better product?
No. Solid content and charge density are different properties. A 40% high-charge product can outperform a 50% low-charge one at the same dose. Compare on cost per unit of charge demand removed.
Notes and disclaimer
- Dose ranges are given as orders of magnitude and as a basis (mg/L in water, or kg per tonne of dry solids) because the correct figure is water-specific. No design dose is quoted.
- The coagulation and flocculation sequence described is the conventional three-stage arrangement; plants with dissolved air flotation, membrane filtration or ballasted settling differ in detail but not in the charge logic.
- Potable water use, residual monomer limits and food-contact approvals are governed by the destination market’s regulation and are not covered here.
Disclaimer. This article describes treatment-program logic for procurement and plant engineering readers. It is not a design specification: the correct sequence, dose and grade must be established by jar testing on the actual water and confirmed in plant trial. Nothing here is a potable-water compliance opinion for a specific market.
For a sample of three grades for a side-by-side jar test, a viscosity figure with its measurement conditions, or a quotation on drums, IBCs and bulk, contact PolyBlueChem.