The most reliable way to choose an iron removal process for landfill leachate is to test several methods side by side on the real liquid. A small skid-mounted pilot plant, treating about 150 litres a day, was proposed to compare settling, coagulation, chemical addition and sand filtration, alone and in combination, to take iron from up to 34 mg/l to below 1 mg/l.

The challenge: iron that blocks reuse

A landfill operator wanted to supply its treated leachate to a nearby public garden for irrigation. To do so, the iron concentration had to fall from as much as 34 mg/l to less than 1 mg/l. That is a reduction of about 97%.

Iron is awkward in irrigation water. It stains and, in the form of iron bacteria, can clog pipes and emitters. The right treatment depends on the form the iron takes in the leachate, how it behaves when oxidised, and how well the resulting solids settle. These are hard to predict on paper. A university student study had already looked at the problem, and the pilot was the next step towards a full-size design.

The approach: one rig, four methods

The pilot was designed so that each treatment step could be used on its own or in any combination. The pipework and valves allow the leachate to be routed through:

1. Settling in a tank, to see how much iron-bearing solid drops out naturally.
2. Coagulation in a tank with a coagulant container, to bind fine particles so they settle or filter more easily.
3. Chemical addition in a further tank with its own chemical supply, to test other dosing routes.
4. Sand filtration to polish the water and remove what remains in suspension.

All of this is mounted on a skid with the pumps, pipework and valves, so it can be moved and set up quickly. The flow is deliberately small, in the order of 150 litres a day. A small flow keeps chemical use, sludge and cost to a minimum while still giving true results.

Why a pilot rather than a design from a table

• Leachate is variable. Strength, pH and oxidation state change with weather and waste age.
• Combinations matter. A coagulation stage may only work if the iron is already oxidised, and a sand filter performs differently depending on what precedes it.
• It sets the full-scale design. Dose rates, tank sizes and filter loading are taken from the trial results.
• It avoids paying for the wrong process. Discovering at pilot scale that one step is unnecessary saves money at full scale.

How the results are judged

Analysis of the treated water was carried out under the client’s own scope, so samples are taken at each stage and tested for iron. The comparison is simple: which route, or combination, reaches below 1 mg/l reliably, at what chemical dose, and with how much sludge. The best-performing option becomes the basis of the full-scale plant.

What to consider for your own project

1. Define the target first. The end use sets the limit. Here, it was 1 mg/l for irrigation.
2. Test enough variables. A rig that can run methods singly and in combination gives far more information than one that can only do one.
3. Plan sample analysis. You need a laboratory able to turn around iron results quickly during the trial.
4. Allow for sludge. Iron removal produces solids that must be dewatered and disposed of.
5. Allow time. This pilot needed about eight weeks to build and four to ship.

For permits relating to leachate, see the Environment Agency’s guidance for landfill operators.

FAQ

What is a pilot plant?

A small version of a treatment process, used to gather performance data on the actual wastewater before designing the full plant.

How much leachate does a pilot treat?

This one was designed for about 150 litres a day.

Why test several methods?

No single method is certain to work. Testing them alone and together shows which is most effective and which is unnecessary.

Is installation included?

In this proposal, no. The supplier delivered the skid, and the client handled installation and analysis.

Need to remove iron from leachate?

Contact us with your leachate analysis and your discharge or reuse target.