Soil pollution constitutes one of the main threats to the health of soil ecosystems in Europe, in terms of complexity, toxicity and recalcitrance. There are about 2.8 million sites potentially contaminated, with 650,000 of them being identified as requiring remediation; among them, only 15% have been already treated [Status of local soil contamination in Europe: Revision of the indicator “Progress in the management Contaminated Sites in Europe” (No. JRC107508), 2018]. Recent estimates found that mineral oil and polycyclic aromatic hydrocarbons (PAHs), also commonly referred to as total petroleum hydrocarbons (TPHs), amount to an estimated mean value of 35% of all contaminants present in European soil. This percentage increase to 50% if BTEX compounds (benzene, toluene, ethylbenzene and xylene) and volatile organic compounds (VOC) are included.

Soil remediation technologies currently available on the market to tackle organic soil contaminations varies between EU countries but mainly consist of landfilling (30% average), physicochemical treatments (i.e. thermal desorption (TD)) (50% average), and conventional bioremediation (5-40%). The first two solutions constitute costly and energy-intensive approaches. Landfilling, in fact, should not be considered as a treatment technology, as only consists in displacing untreated polluted soil to confinement. Thermal treatment, although it has the clear advantage of being a short time process, is highly energy consuming in all the stages leading to average greenhouse gas (GHG) emissions of up to 70 kg CO2-eq/m³ soil treated (J. Clean. Prod. 186:514). Moreover, it results in the generation of a “dead” – albeit cleaner- soil.

Conversely, bioremediation can be performed on-site on excavated soil arranged in biopiles (150-1000 m³ of soil each). Biopiles are engineered to stimulate either indigenous or allochthonous bacterial activity and to boost biodegradative metabolism, thus ensuring organic pollutants breakdown to mineralization. This remediation technology is the most environmentally friendly solution available on the market so far, as it is less energy-intensive (only required for soil excavation and aeration) and it has no detrimental impact on soil functions. However, its major limitation is the low removal efficiency of long-chain TPHs: TD is able to remove >99% (Engineering (2016) 2:426) while bioremediation remediation percentages might be as low as 20% for weathered TPHs (Int. J. Environ. Sci. Technol. 12:3597).