A comprehensive review on the bioremediation of oil spills

Oil spills are probable accidents occurring mostly during transportation and processing of oil that can contaminate marine, soil, sediments, and other environments. Oil spill is a special challenge to be remediated due to its several environmental, economic, and social threats. Several physical (mechanical), chemical, and biological methods are available as response to the oil spills. Among them bioremediation proved to be a promising technique for treatment of oil spills especially after being applied successfully for Exxon Valdez oil spill. Bioremediation is a greener approach in comparison with physicochemical methods, which is more cost-effective with less disruptive effect on the environments. In this method the natural or genetically manipulated microorganisms are applied to the polluted site and/or the polluted environment is enriched with nutrients, which are called bioaugmentation and biostimulation, respectively. These methods have been examined by researchers for treatments of oil spills mostly in laboratory scale and in less extent in real fields. One novel approach in this area of the research is focused on the novel material addition to the polluted environment for biostimulation of the treatment process. Novel materials include organic sources to provide nitrogen and phosphorus for the medium such as compost, biowastes, biofuel, etc. Biosurfactant addition is another promising method that improves the bioremediation by reducing the surface tension. Some polymeric materials can be added for improving the immobilization of microorganisms and consequently enhancing the degradation rate. Novel bioaugmentation approaches are conducted by manipulating microorganisms with the aim of modification of enzymatic characteristic, metabolic pathway design, expansion of substrate rate, enhancing the genes resistance toward catabolic activities, etc. However, still there are several resistances toward the application of these microorganisms to the real field, due to the environmental concerns. Another novel approach is the integration of electrochemical methods and biological routes. Several achievements were reported by researchers for the remediation of oil spills by using bioelectrochemical systems (BES). Microbial fuel cells are another technique to convert chemical energy into electricity concurrent with contaminant degradation. The future research on the oil spill bioremediation must be focused on these new aspects of the process and finally pave the way for application of bioremediation in real field to obtain promising pollutants degradation results.