Rehabilitating a landfill site is a process that takes place in several stages.
It all starts with the civil engineering works :
- as a first step, SPAQuE performs a site reprofiling: the aim is to create slopes favourable to rainwater runoff, to better compact the waste and to "landscape" the landfill so that it blends into its surroundings,
- then, SPAQuE performs a capping of the site so as to prevent the infiltration of rainwater and the diffusion of volatile pollutants, thereby insulating the landfill. While many forms of capping exist, the basic principle consists (from top to bottom) of a plantable layer, a draining layer and a waterproof layer (natural and/or artificial),
- SPAQuE then installs two separate networks to manage leachate, on the one hand, and biogas, on the other. These networks usually consist of wells and air collectors,
- finally, some additional work is carried out, for example, rainwater drainage, development of technical areas and internal roads, planting of surfaces, fencing, etc.
Once these works have been completed, the actual management of the biogas and leachate can begin. Biogas is a gas produced by the anaerobic fermentation of organic matter in the waste. It consists of two main elements : methane and carbon dioxide, as well as trace elements such as BTEX, sulphides, etc. The composition of biogas varies according to the age of the landfill and the type of waste. Besides being evil-smelling, it is also highly toxic and explosive. To manage this biogas, an extraction device is installed. The biogas can then be burnt off or used as a fuel thanks to a boiler or co-generation units (engines or microturbines) that allow the production of heat and power, or simply be filtered through activated carbon.
Leachate, the liquid produced by the percolation of the water through the waste, is treated in two stages :
- temporary management for 12 to 24 months during which the leachate is analysed and processed on a temporary unit (to identify accurately the quality and quantities),
- definitive management over the long term, during which the leachate is treated by a definitive unit, sized according to the needs identified during the previous stage.
Note that the management of leachate depends on the configuration of the landfill site : fully contained, natural containment, capping, etc.
The final stage is the post-management of the landfill site. It consists of :
- equipment maintenance,
- analytical monitoring of the biogas, leachate, piezometers and atmospheric emissions,
- general site maintenance (mowing, repairing fences, etc.).
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