When a batch fails the paint filter test twice

The first failure is a data point. The second is a pattern, and you are now standing on a pad with a tanker booked for 16:00, a batch that will not hold, and an operator adding polymer in the hope that more will fix it. That hope is usually wrong, and it is expensive.

A double failure means the cause is not random variation. Something in the dose, the mixing, the material or the liquid has changed, and adding polymer without identifying it usually produces a third failure at higher cost.

What a double failure rules out

It rules out operator fatigue, a single mis-weighed bag and a one-off wet lot. Those produce single failures. Two in a row points to something systematic: a dose that was already at the margin, a mixing step that has stopped working, a polymer lot that is not what the label says, or a leachate change that has moved the target.

It also rules out the test itself being the only problem, though not entirely. Check the filter and the timing before anything else, because a clogged filter or a shorter drain period will fail a good batch. That takes two minutes and eliminates the cheapest explanation.

The 45-minute diagnostic sequence

First, re-run the test on a fresh sample from the middle of the tank, with a clean filter and the full drain time. Second, run a jar test at the current dose, at plus 15 percent and at plus 30 percent, and note not just pass or fail but how the floc forms. Third, check the polymer lot against the last good batch, including the bag date and the supplier’s certificate. Fourth, check the water temperature and the mixing time against the batch sheet.

One of those four will usually explain it. The order matters because the cheapest checks come first and the most disruptive — re-batching — comes last.

When to stop adding and start again

If the plus-30 percent jar still produces free liquid, more polymer is not the answer. Either the leachate has changed in a way that needs a different grade or a pre-treatment step, or the batch has been over-mixed and the gel structure has broken down. Both require a new batch, not a longer mix.

Set a rule in advance: no more than two incremental additions to a single batch. After that, discharge to a holding tank, re-test the liquid and start fresh. The holding tank costs less than a third and fourth addition, and it keeps the trailer schedule honest.

Tell the haulier early. A truck that arrives to find no load ready will charge for the trip, and a phone call at 13:00 costs nothing.

The lot that was not what it said

A site failed two batches on a Tuesday, added 40 percent more polymer to the third, and failed that too. The polymer had come from a new delivery, and the bags looked identical to the previous pallet. A retained sample from the previous lot gelled normally at the standard dose; the new lot needed almost double.

The supplier’s certificate showed the correct grade, but the particle size distribution was visibly different — much finer, with a high fines fraction that clumped on contact and never fully wetted. The site had been dosing unreacted powder and measuring the result as a dose failure.

The lesson is to keep a retained sample of every lot and to run a bench check on the first batch after any delivery. Twenty minutes at the bench prevents a day of chasing a problem that was never in the leachate.

If your last two failures have not been written down with the dose, the lot number and the batch temperature, that record is the first thing to build. The solidification operating guide includes a failure log format that makes the pattern visible after the second event rather than the fifth.