Leachate Management Techniques
General
The starting point in any discussion about UK/ EU leachate management techniques is to begin by stating the overriding assumption upon which all landfills are operated in compliance with the EU Landfill Directive. That is that as far as practicable the waste will be kept dry and all leachate generation will be minimised by doing this. So the exposed cells are kept as small as possible and capped as soon as practicable with low permeability materials.
Nevertheless, despite such measures most landfills do still generate leachate, and the first and most obvious action, when leachate starts to appear, is to recirculate it by pumping it back on to the surface of the waste in the hope that it will soak into the wastes and not reappear. Certainly, this will be possible for a period of time under most circumstances.
Other techniques which do not strictly comprise “treatment”, have been utilised, such as:-
- leachate irrigation on to nearby land or the restored landfill surface: to achieve volume loss by evaporation - may work in dry summers, but not much use during the average UK winter, nor in many summers! (Since this was first written leachate irrigation has ceased for all new and current landfills, and can now only be considered as part of a beneficial use scheme.)
- dilution of leachate with surface water from the site, to bring contaminant concentrations below watercourse and sewer consent levels and by so doing allow themselves the use of these disposal routes. This is not normally justifiable in the UK against sustainability criteria, and will now also be likely fail to comply with the principles of BAT (Best Available Technique) under Environmental Permitting (IPPC Regulations);
- leachate “pre-conditioning” our term for the chemical/physical modification of problematic contaminants in sewage. Such “pre-conditioning” might for example comprise the addition of hydrogen peroxide, or potassium permanganate to an odorous leachate to reduce smells, or the common use of Methane Stripping which uses air and mixing to dissipate dissolved methane to the atmosphere from leachate.
 However, in recent years the instances where “pre-conditioning” is used have become rare in the UK, and it is difficult to envisage anything beyond short term/emergency use of such methods.
The continued use of all the above is (February 2005) under review, and many of the above may no longer be permitted when new BAT guidance currently being prepared by Enviros with the Agency is implemented. (See News item.)
Other common practices under review by the UK Environment Agency include the continued acceptability of tankerage of leachate to sewage works licensed to accept industrial effluent, where there is not comprehensive treatment at the receiving sewage works, and also discharge to public sewers if these similarly lack sufficiently the facilities to treat all the major contaminants of leachate, rather than just diluting it.
Leachate Recirculation
Leachate recirculation has been practised at nearly all landfills for periods during the life of a landfill. From the point of view of good leachate management leachate recirculation, while often likely to increase the strength of the recirculated leachate during each pass, recirculation will usually provide benefits, as follows:-
- When a cell is new recirculation can accelerate waste settlement and stabilise the waste mass, and bring forward the start of methanogenesis (as long as the recirculated leachate does not cool the waste mass, does not cause complete saturation of the waste mass, or introduce excessive oxygen);
- Recirculation can help reduce the initial very high acetogenic BOD/COD stage which places a higher oxygen demand on the leachate treatment facility than needed later in the site life;
- During very wet weather periods, recirculation can simply temporarily "store" peak leachate flows, while they percolate through the waste and arrive again at a leachate collection point, and hence allow the leachate treatment facility to be smaller and more cost effective.
The method of leachate recirculation will require agreement with the site regulator. Nevertheless, recirculation has been practised on most landfill sites for periods in the “active” life of the landfill
With the current implementation of IPPC Regulations to landfills now progressing, the EA (UK) are reviewing the context and acceptability of recirculation as a leachate management technique.
See also our more comprehensive leachate recirculation page.
Up. See also Leachate Treatment - an Introduction.
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