The received soil undergoes one or more of the following four types of processing:

  • Mechanical pretreatment (screening and grinding), to separate the exogenous materials and make the pollutants accessible to break-down by micro-organisms. Any metals that they contain may also be removed. A large proportion of the materials gleaned at this stage is already of good-enough quality for recycling.
  • Biological processing (bioremediation), based on the ability that certain micro-organisms have to use the polluted organic fraction as a growth substrate (for respiration and weight gain) and thus break these compounds down into water and carbon dioxide. The first step is to promote the growth of the most suitable endogenous micro-organisms. Once they have been multiplied, they are then disseminated in homogeneous batches of soil that then undergo several weeks of processing.
  • Physical processing (washing):  The soil may undergo wet physical processing that consists of screening under pressurised water, various washing steps, and spin drying. The plant is mobile so that it can be brought on site for several weeks of washing and screening stockpiled soil. This type of processing makes it possible to remove heavy metals from the earth.
  • Bioventing: The soil is windrowed under airtight membranes, and then a stream of air is forced through to recover the volatile pollutants, which are trapped in an active charcoal filter.

Whatever the processing method chosen, the decontamination of the materials is monitored by batch testing to keep tabs on the appropriate pollution indicators before, during, and at the end of the processing.