Five Leachate Streams Where Solidification Makes Things Worse

Every supplier in this business has a story about the job they should have turned down. Ours was a lagoon of dilute leachate at a transfer station: 400 m3 at under 1% dry solids, and a plan to solidify the lot for road transport. The arithmetic said 90 tonnes of polymer and 480 tonnes of wet gel. The client went with a vacuum tanker instead and paid a fifth of that. They were right and we were slow to say so.

What Solidification Is Actually For

It binds free water so a liquid can be handled, stacked, transported and accepted. It is a handling technology, not a treatment technology. It does not remove ammonia, chloride, sulphate or dissolved metals, and it does not reduce the mass of contamination — it changes the physical form. Everything that follows depends on understanding that distinction.

Five Streams to Refuse, or at Least Question Hard

High-volume, low-strength leachate is the first. Below about 2% dry solids and above a few hundred cubic metres, you are mostly buying polymer to move water. A tanker, a membrane plant or an on-site evaporator will beat solidification on cost per cubic metre nearly every time. Solidification starts to win when the volume is small, the site has no treatment capacity, or the material must leave the site in a non-liquid form by regulation.

Second, anything with high oil and grease. Free oil coats the granule before it can hydrate. Above roughly 500 mg/L of oil and grease, absorption falls off a cliff and you get a greasy, unsolidified sludge that fails every acceptance test while consuming full dose. Skim or separate first; polymer is not a degreaser.

Third, streams that already have a legal discharge route. If the leachate goes to sewer under a consent with limits you can meet, solidifying it converts a controlled discharge into a waste that must be hauled and landfilled. You have added cost and a waste stream in exchange for nothing. Check the consent before the polymer, every time.

Fourth, cases where the regulator wants leachability rather than free liquid. This is the one that catches people. A solidified block can pass a paint filter test and still release chloride and ammonia at concentrations that fail a leaching test, because those species are dissolved in the gel water and diffusion does not stop at the gel boundary. If the acceptance criterion is leaching-based, solidification alone rarely satisfies it and may need a cement or lime-based stabilization instead. Ask which test governs before you dose anything.

Fifth, very saline or highly alkaline streams. Conductivity above 40-50 mS/cm, or pH above 11, suppresses swelling so severely that the required dose becomes uneconomic. At that point you are using polymer as a thickener and should price it as one, with realistic expectations about the result.

A One-Page Decision Rule

Solidify when three things are true: the volume per event is under about 50 m3, there is no permitted discharge route or treatment plant available in time, and the acceptance test is physical rather than leachability-based. If two of those fail, model the alternatives before buying a single bag.

The honest caveat on all of this: the thresholds above are rules of thumb from field work, not regulation. A site with a 200 m3 lagoon and no other option at 6 p.m. on a Friday should solidify, and the fact that the economics look poor on paper does not change what the permit officer will accept. The point is to know which trade you are making and to price it honestly, rather than to discover it in the second week of a contract.

When solidification is the right call, the grade matters more than the dose — the range we supply for difficult, saline and cold streams is listed on our leachate solidification polymer page.