Contamination or pollution of our environment has become a real global concern, especially in parallel with the increasing evolution of urbanization and industrialization, which in turn have released a plethora of different pollutants that end up being deposited in soils. It is crucial to investigate solutions that can minimize the extent of damage, and that are cost-effective, feasible and environmentally friendly, to treat a wide variety of contaminants in soils, as well as to detoxify various compounds. Bioremediation is a safe technique that has demonstrated satisfactory results and is easy to apply and maintain. This technique explores the degradation pathways of various biological agents (microorganisms, plants, algae, etc.) to neutralize contaminants. It is based on biodegradation through a complete mineralization of organic pollutants into inorganic innocuous compounds, such as carbon dioxide and water. This review aims to determine the feasibility of bioremediation as a cleanup technology for soils contaminated with pesticides, agrochemicals, chlorinated compounds, heavy metals, organic halogens, greenhouse gases, petroleum hydrocarbons, and many others, either in situ or ex situ. Different bioremediation approaches are described and compared, showing their advantages and drawbacks from a critical point of view. Moreover, both the economic and technical barriers of bioremediation are addressed, along with the outlook for the role of microorganisms in the process, the aim to identify future directions, and the application feasibility of this process.

Oil pollutants affect the mechanical properties of soils differently. The effect of the kind of oil pollutants on the geotechnical characteristics of a type of soil is an interesting subject that has been examined less in previous studies. The results of this research can be used in designing structures built on soils that are likely to be contaminated with oil pollutants. This study comprehensively investigated the effect of the type of pollutants on the mechanical properties of sandy clay soil to provide the necessary parameters in the remediation plan for soils contaminated with various oil pollutants. A series of laboratory tests, including pH, standard compaction, one-dimensional consolidation, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), falling head permeability, and direct shear, was conducted on the clean and polluted samples. Scanning electron microscopy (SEM) micrographs confirmed that oil pollutants change the soil structure into a flocculated but dispersed one. In addition to the low dielectric constant of oil pollutants, their high viscosity played an important role in altering the geotechnical parameters of clayey sand. The higher the viscosity of the oil pollutant, the higher the maximum dry density (MDD), cohesion coefficient, compression index (Cc), swelling index (Cs), and permeability coefficient of oil-polluted soil. The samples polluted with used motor oil and crude oil, due to their high viscosity, had the greatest drop in compressive strength and shear strength, respectively; whereas the kerosene-polluted sample, due to its low viscosity compared to other oil pollutants, had the greatest rise in compressibility. Thus, in geotechnical plans, special attention should be paid to the bearing capacity and settlement of clayey sand contaminated with crude oil and kerosene, respectively. Oil pollution alters the mechanical properties of soil and poses hazards to the environment.The low dielectric constant and high viscosity of oil pollutants play important roles in changing the properties of soils.Used motor oil greatly reduces the compressive strength of clayey sand, while crude oil and kerosene make the shear stress and settlement of clayey sand more critical, respectively.