Soil remediation techniques
Because of the extensive use of petrol and its products the presence of polluting compounds, like petroleum hydrocarbons and PAHs in soil is a significant common problem that constitutes a serious danger for the public health due to the toxicity of many of them. Hydrocarbons, due to their lipophilic nature, attach to the ground, where they might either stay or be washed off, polluting the aquifers, while most of the volatile hydrocarbons which are in most cases the most toxic ones aren’’t sorbed on the ground, reducing the quality of air in the polluted areas. For this reason, numerous methods have been developed for the remediation and restoration of the polluted areas.
“Soil remediation” refers to any kind of action aiming at the reduction or elimination of the dangers for public health due to soil pollution. Remediation methods are based either on the physico-chemical properties of PAH and petroleum hydrocarbons in general, or on the possibility of bio-degradation. The selection of a specific method depends on the pollutants nature, soil’s condition, and the required cost.
Remediation methods can be divided into two sub-categories:
In situ methods: they do not require excavation and transfer of the polluted soil and the treatment is performed in situ.
Ex situ methods: they require excavation and transfer of the polluted soil and the treatment is performed elsewhere.
It is understandable that the ideal remediation method is the one that ensures the best results possible at the lowest cost. The best method for the complete removal of organic compounds in soil is incineration. This method, however, as well as others that are based on incineration for the removal of pollutants is expensive, require the excavation and transportation of the soil, complicated processes for the production of the sludge that will be used as fuel, and proper facilities. In addition to that, the soil is fully sterilized and all of its’’ organic load is destroyed, while there is always a danger of atmospheric pollution if the burning conditions are not successfully optimized.
Thus, other milder methods of biological and chemical remediation have been developed, which utilize micro-organisms and chemical reactions respectively for the removal of the polluting compounds. These methods are applicable for the degradation of a wide range of organic pollutants and many of them can be applied in situ, requiring, though, careful optimization for each case.
|Bio-restoration||Bio-reactor||Applications of indigenous and isolated microorganisms under controlled conditions, high degradation rate,use of sludge,non-toxic residues,application in situ,non prohibitive cost|
|Landfarming||Use of indigenous microorganisms and inorganic fertilizers, low degradation rates, possibility of surface and underground aquifers pollution,relatively low cost|
|Biopiling/composting||Use of indigenous micro-organisms inorganic fertilizers and air, low degradation rates, possibility of polluting superficial and underground waters|
|Bioventing||Combination of soil ventilation and bio-remediation for field usage,volatile hydrocarbons are vaporised|
|Biostimulation/Bioaugmentation||Applying inorganic nutrients,surfactants and/or micro-organisms for the stimulation or the augmentation of the indigenous micro-organisms of the polluted soil, low cost,need for optimization|
|Natural attenuation||Observation of the degradation process, it can’t be used in cases of high pollutant concentrations.|
|Phytoremediation||Use of plants and micro-organisms of the rhizosphere fro the removal of ΤΡΗ, low cost,inability of removing high concentrations|
|Physicochemical restoration||Incineration||High temperature, danger of atmospheric pollution,expensive mechanical equipment,sample transfer,high cost|
|Thermal desorption||Method for the removal of petroleum hydrocarbons from soil using high temperature, high cost,non-toxic residues|
|Coker||Complex process for the production ofsludge for the supply of coker, high functional and transfer cost|
|Cement Kiln||Complex process for the production of sludge, high material,functional,transfer and waste disposal cost|
|Soil washing||Use of surfactant compounds for the removal of pollutants|
|Extraction with organic solvent||Use of solvents along with centrifugation or filtration for the separation of petroleum from the sludge,solvent pollution, high cost|
|Chemical reaction||Use of a chemical reaction for the oxidation of the pollutants,need for the control of pH,total oxidation of all the compounds in soil, high cost|
This research project that was funded by the Research Promotion Foundation of the Republic of Cyprus aims at the introduction of an environmentally friendly remediation method for soil polluted with petroleum products in the environmental and climatic conditions of the island. Four research groups cooperated for the accomplishment of the project’s goals, with significant experience in these research fields.