school energy&environment

The waste dump or landfill

In the controlled type of dump, waste is deposited in layers on the ground, in a suited and monitored manner, so as to minimize the negative effects on the environment and on human beings. Thus pollution of surface and underground water is prevented and controlled, as also emissions of unpleasant or toxic substances, and all efforts are made to reduce the aesthetical impact. Even though the disposal of waste in dumps is the least efficient type of waste management, in Italy this is still the solution that is mostly adopted in almost one case out of two.
Dumps can be subdivided into three different areas: an internal mass, which is the largest area, where degradation of putrescible waste takes place in absence of oxygen (anaerobic degradation with the formation of biogas), a superficial layer, that acts as an interface between the solid mass and the air; the leachate, the liquid produced by rain water  percolating in the waste and the humidity content of the waste. Waste dumps are created by successively filling layers of a suited height (maximum 2.5 m) starting from a bottom layer that has been suitably waterproofed with natural materials (clay or a mixture of sand and bentonite) or artificial materials (geomembrane made of PE and PVC). Once the layer of waste has been laid down, it is compacted with mechanical equipment (bulldozers or compactors)  to decrease the volume these occupy,  up to a density of about 800 kg of waste per cubic metre. Every day, the waste is covered with inert material such as soil or gravel, and when the dump is fully filled, it is entirely covered with vegetative land, and usually it is converted into a green area. An important element of the dump, are the drainage system and the system for the collection of biogas and the leachate, to avoid contamination of the area.
All this occurs in controlled waste dumps, however often the dumps are associated with very negative characteristics, because of the risks involved for the environment and human health, besides their unpleasant aesthetical problem.
This is true with regard to non-controlled and illegal dumps that are very dangerous. Controlled waste dumps, per se, are not negative, but their utilization must be limited as much as possible and only where valid alternatives are not available. As we have pointed out before, in fact, the waste dump is the last solution in the hierarchy of waste management alternatives.  There are many reasons for this: first of all waste sent to the waste dump is no longer useful and from this waste nothing can be recovered neither as a material nor as energy; furthermore the waste dump needs large amounts of space in order to be constructed, and a large effort with regard to the costs and for management of the same. The space and the resources that are available on the planet are not infinite and in this view, use of waste dumps implies a large amount of wasted resources.