Landfill Leachate

Landfill leachate is the liquid formed within a landfill site. It is formed by a mixture of liquids present in the fill deposited into it and rain water. Some particularly old landfills that were not engineered i.e. are not impermeable, may have aquifers running through them - adding to the volume present.

The chemical make up of the leachate varies dependant on the products taken in for disposal. Typically, the leachate will be composed of a range of compounds including nitrogen, organic carbons, chlorides, phenols, solvents and heavy metals.

The complex chemistry of the leachate and the difficulty in abstracting it from within the fill can make management particularly onerous. Especially as the Waste Management Regulations are rigorously enforced by the relevant regulatory bodies.

Generally most landfills adopt a grid system of boreholes penetrating down almost to the base of the landfill. These boreholes must be carefully designed to ensure longevity of use as the landfill shifts and settles, and also to induce as much flow of leachate into it, particularly as many historic daily cover systems were not placed with permeability in mind.

Once abstraction wells are in place the equipment to abstract it needs careful consideration. Most now require intrinsically safe equipment such as pneumatic pumps or eductor/ejector systems. These use/create a venturi effect to recover the leachate. This method is being used very successfully across the United Kingdom.

Treatment of landfill leachate, due to its complexity, remains difficult and expensive. Most systems involve either aerobic or anaerobic bioremediation along with sediment removal and often some chemical or nutrient addition, which, once completed, allow disposal to the foul sewer.