Biodegradation of the Soils Polluted with Ethyl Benzene, Toluene and Naphtalene

Background & Objective: Aromatic hydrocarbons are produced by incomplete combustion of fossil fuels and pollute the soil following the emission into the atmosphere by precipitation. Numerous studies suggest that microbial inoculation has contributed to biodegradation of aromatic hydrocarbons. However, other studies have not confirmed the efficacy of this procedure in biodegradation. Regarding the contradictory findings, this study was conducted to evaluate capability of microorganisms isolated from oil-polluted soils in biodegrading aromatic hydrocarbons through separate or mix culture in Zanjan in ۲۰۰۴. Materials & Methods: In this experimental study naphthalene, toluene and ethyl benzene were used as aromatic hydrocarbons indexes. These substance, as the sole source of carbon were added to the soils which had been inoculated with microbial colonies isolated from polluted areas and four months later microbial count was performed as microbial activity index. The extent of biological and non-biological removal of substances was assessed through gas chromatography procedure and the results were analysed by Mann-Whitney test. Results: Mean colony counts in which toluene, ethyl benzene and naphthalene had been used as the sole carbon source were ۱۹.۷×۱۰۶, ۶۹.۴× ۱۰۵ and ۴۱.۲×۱۰۶ colony/gr. soil respectively. In the culture containing a mixture of three hydrocarbons the number of colonies was ۳۴×۱۰۶ in one gram soil. The percentages of biodegradation for three studied hydrocarbons which had been exposed to microorganisms separately were ۵۱, ۴۵ and ۶۹ for toluene, ethyl benzene and naphthalene respectively and when the mixture of the substances was added to the media culture the percentages of removal were ۸۰.۱, ۶۵.۷ and ۶۳.۶ for naphthalene, ethyl benzene and toluene respectively. Conclusion: Aromatic hydrocarbons are biodegradable by isolating microbial population from oil-polluted soils and preparation of inoculation liquid. Since evaporation is an appropriate method in removal of hydrocarbons, soil rehabilitation through aeration together with microbial inoculation seems a proper method for removal of soil aromatic hydrocarbons.

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Key words: Aromatic hydrocarbons , Soil , Biological degradation