Leachate is a product derived from the anaerobic transformation of the organic substances present in the waste. It is a liquid with different levels of pollutants present, the form and quantity of which will depend on factors such as the type of landfill, and the quantity of rainwater which filters through the landfill, mixing with the humidity of the waste itself. Due to the high level of pollution present the leachate has to be contained and treated so as to avoid the pollution of the water table or of the environment. The leachate is highly variable from a qualitative and a quantitative point of view, both from one landfill to another, and within the same landfill, due to the fact that the concentration and flow are both closely connected to values of atmospheric precipitation.
There are only a few techniques used for the treatment of the leachate, and the physical applications which allow the 'clean' water to be separated from the raw leachate are those most frequently applied.
An example of this is the landfill at Roccasecca (Italy) where the C&G vacuum evaporators have been applied to form an integral part of their highly organised structure.