Comparing two polymer suppliers on the same month’s data

Two quotes arrived in the same week: 4.10 and 4.35 per kilogram. The cheaper one looked like an easy decision until we ran both products across the same month of batches and found the real cost per cubic metre was 18 percent higher on the lower-priced material.

Comparing polymer is not a price comparison. It is an experiment, and like any experiment it is only as good as the things you hold constant.

Hold these four things fixed

Leachate batch, water, operator and mixer. If the two products are trialled on different days with different leachate, the result is noise. Take a single homogenised batch of leachate — 20 m³ in a stirred tank is enough — and split it into identical sub-batches.

Use the same operator for both, because dosing technique varies more between people than between products. Use the same mixer at the same speed. Record water temperature, because a 6 °C difference changes wetting time enough to confuse the comparison.

The four metrics that decide it

Kilograms per cubic metre to reach your acceptance standard, time to reach it, cake solids, and free liquid after two hours. The first is the obvious one; the second and third usually decide the argument.

A product that needs 5 percent more polymer but sets in half the time can be cheaper overall if your bottleneck is the mixer rather than the store. A product that produces 3 percentage points more cake solids reduces the volume you haul, which on a per-tonne disposal charge can outweigh a 6 percent price difference. Run the numbers on your own haulage rate before assuming the cheaper bag wins.

Watch for the grade behind the label

Two suppliers can both quote “leachate grade” and deliver materially different products: different particle size distribution, different crosslink density, different residual monomer, different dust level. Particle size matters more than most buyers realise, because fines wet fast and clump, while coarse granules disperse slowly and leave fish eyes.

Ask both suppliers for the same six data points on the same lot: absorbency in deionised water, absorbency in 0.9 percent saline, bulk density, particle size range, moisture content and pH of a 0.1 percent dispersion. If a supplier cannot provide saline absorbency, that is itself information, because saline performance is what predicts behaviour in high-conductivity leachate.

Run the trial for a month, not a day

A single-day trial tells you which product works. A month tells you which product is consistent. Split the month into two halves, run product A for two weeks and product B for two weeks, and log dose, batch time, cake result and any rejected loads. Then swap the order for a second month if you can, so that a change in leachate strength does not get attributed to the product.

Keep the samples. If the results surprise you, a retained 500 g sample from each lot will explain more than any amount of discussion with the sales team. Keep the batch sheets too, because the day-to-day record of mixing time and operator is the only way to tell a product difference from a shift difference.

Finally, put a number on switching cost before you decide. Sampling, staff time, rejected loads during changeover and the risk of a failed month all belong in the comparison, and on a site handling 3,000 m³ a year they are rarely less than the price gap that started the conversation.

The cheap bag that cost more

One site switched on price and saw dose rise from 2.3 to 2.9 kg/m³ over six weeks. The new product had a finer grind, which the supplier presented as a benefit because it wetted faster. In practice the fines clumped on contact with the leachate surface and formed gelatinous balls that took ten minutes of mixing to break up.

The site went back to the original supplier, but kept the trial data and used it in the next tender. The specification now names a particle size range and requires a saline absorbency figure on the COA. The price difference between the two quotes was 6 percent. The cost difference was 18.

If you are about to run a comparison, write the protocol before the samples arrive, and agree in advance what result would make you switch. The SAP product range lists the properties worth specifying, which makes for a fairer conversation with any supplier.