The soil, the most superficial layer of the earth’s crust, constitutes one of the most important natural resources with which we have to be the substrate that sustains life on the planet. The soil provides the nutrients, water and physical support necessary for plant growth and the production of biomass in general, playing a fundamental role as a source of food for living beings.
It is an essential component of the hydrological cycle, acting as a distributing element of surface water and contributing to the storage and recharge of groundwater. The soil, through its buffering or natural deactivation of pollution, filters, stores, degrades, neutralizes and immobilizes toxic organic and inorganic substances, preventing them from reaching groundwater and air or entering the food chain.
According to the FAO, soil degradation can be defined as any process that reduces the current and potential capacity of the soil to produce, quantitatively and qualitatively, goods and services. These degradation processes can be classified according to their nature and the type of negative consequences they cause on soil properties: biological, such as the decrease in the content of organic matter incorporated in the soil; physical, as the deterioration of soil structure by compaction and increase in bulk density, decrease in permeability and water retention capacity or loss of soil by erosion; and chemicals, such as the loss of nutrients, acidification, salinization, sodification and increased toxicity.
In recent years, many investigations have been aimed at trying to recover contaminated soils instead of destroying them. The destruction of the soils is generally carried out by transferring them to landfills properly isolated and controlled because it is intuited that other recovery treatments do not offer sufficient guarantees to contain the contamination. At present, there is a wide range of technologies for the recovery of contaminated soils, some of which are customary and others still in an experimental phase, designed to isolate or destroy polluting substances by altering their chemical structure through generally chemical, thermal or biological processes.
According to the way in which soil recovery techniques are applied, there is talk of in situ treatments, which act on the contaminants in the place where they are located, and ex situ treatments, which require the previous excavation of the soil for later treatment. In situ treatments require less management but are generally slower and more difficult to carry out given the difficulty of putting decontamination agents in close contact with the entire mass of contaminated soil.
Ex situ treatments are usually more expensive but also faster, usually achieving a more complete recovery of the affected area.
Depending on the objectives you want to achieve when recovering contaminated soil, you can distinguish between: • Containment techniques; that isolate the contaminant in the soil without acting on it, usually by applying physical barriers in the soil.
• Confinement techniques; that reduce the mobility of contaminants in the soil to prevent their migration by acting directly on the physicochemical conditions under which the contaminants are found.
- Decontamination techniques; aimed at reducing the concentration of contaminants in the soil.