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Bioremediation is a soil clean-up technique which exploits the metabolic capacity of microorganisms to degrade soil contaminants. A model was developed to simulate the ex situ bioremediation of a diesel-contaminated soil in a bio-slurry reactor inoculated with a diesel-degrading bacterial strain. Mass transfer processes involving desorption of diesel from soil to water and volatilization of diesel from water, and biodegradation by the bacterial inoculant were included in the model by using Weibull sigmoid kinetics and logistic/Monod kinetics respectively. Model parameters were estimated in batch-based abiotic and biodegradation experiments. Sensitivity analysis revealed the importance of maintaining a high bacterial density in the system for maximum bioremediation efficiency. The model was validated using a pilot bioreactor monitored for 528 h, which removed almost 90% of the diesel present in the system. The results revealed the capacity of the model to predict the bioremediation efficiency under different scenarios by adapting the input parameters to each system., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Selenium concentrations in the soil environment are directly linked to its transfer in the food chain, eventually causing either deficiency or toxicity associated with several physiological dysfunctions in animals and humans. Selenium bioavailability depends on its speciation in the soil environment, which is mainly influenced by the prevailing pH, redox potential, and organic matter content of the soil. The selenium cycle in the environment is primarily mediated through chemical and biological selenium transformations. Interactions of selenium with microorganisms and plants in the soil environment have been studied in order to understand the underlying interplay of selenium conversions and to develop environmental technologies for efficient bioremediation of seleniferous soils. In situ approaches such as phytoremediation, soil amendment with organic matter and biovolatilization are promising for remediation of seleniferous soils. Ex situ remediation of contaminated soils by soil washing with benign leaching agents is widely considered for removing heavy metal pollutants. However, it has not been applied until now for remediation of seleniferous soils. Washing of seleniferous soils with benign leaching agents and further treatment of Se-bearing leachates in bioreactors through microbial reduction will be advantageous as it is aimed at removal as well as recovery of selenium for potential re-use for agricultural and industrial applications. This review summarizes the impact of selenium deficiency and toxicity on ecosystems in selenium deficient and seleniferous regions across the globe, and recent research in the field of bioremediation of seleniferous soils.

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. [ABSTRACT FROM AUTHOR]