Using of Indigenous Microorganisms to Reduce Petroleum Contamination in Tehran oil

IntroductionPolycyclic Aromatic Hydrocarbons (PAHs) are widely distributed contaminants which have drawn increasing public health concern because of their mutagenic and carcinogenic properties. In addition to their natural occurrence, anthropogenic inputs from fuel combustion, pyrolytic processes, waste incinerators, domestic heaters and spillage of petroleum products have resulted in a significant accumulation of PAHs in the environment. Petroleum contaminated soil is currently treated using three types of processes: physical, chemical, and biological. Bioremediation is an attractive approach for cleaning up petroleum hydrocarbons, because it is simple to maintain, applicable over large areas, cost-effective and leads to the complete destruction of contaminants. Organic compounds are metabolized under aerobic or anaerobic conditions by biological processes of microorganisms. Bioremediation of contaminants can be accomplished by two methods, bioaugmentation and biostimulation. The process of bioaugmentation, as it applies to remediation of petroleum hydrocarbon contaminated soil, involves the introduction of microorganisms that have been cultured to degrade various chains of hydrocarbons into a contaminated system. The process of biostimulation introduces additional nutrients in the form of organic or inorganic fertilizers into a contaminated system, which increases the population of the indigenous microorganisms. In the field of biostimulation, nutrient supplementation for hydrocarbon degradation has traditionally focused on the addition of N and P. Because C is a major constituent of petroleum fuels, its traditional role in bioremediation research has typically been as an index to determine the amount of N and P that needs to be added to reach the optimal C:N:P ratio. The indigenous microorganisms of the contaminated soils, which are adapted to hard conditions, are the best microbial population for using in bioaugmentation. Various microorganisms have different requirements for using the carbon contents of pollutants as an energy source. Thus, the successful application of bioremediation technology to contaminated soil requires knowledge about the characteristics of the site and the parameters that affect the microbial biodegradation of pollutants. This study was carried out to isolate high diversity of bacterial strain with the ability of degrading multiple PAHs from Tehran oil refinery contaminated soil and obtain the optimized conditions of biodegradation of these pollutants in laboratory. The final objective was to compare the effectiveness of natural attenuation, biostimulation and bioaugmentation for PAHs degradation in soil. Materials and MethodsSoil samples were collected in sterilized panels from four different geographical directions of a land next to the active units of Tehran oil Refinery in Iran. The soil properties of samples are provided in Table.1. The presence of PAHs contamination in the soil of this land was confirmed by solvent extraction (Dichloro methane) in an ultrasonic water bath and high HPLC analysis.