using indigenous microorganisms to reduce petroleum contamination in tehran oil refinery contaminated soil

poly aromatic hydrocarbons are hydrophobic organic compound found as major contaminants in soil. soil biological activities are vital for the restoration of soil contaminated with hydrocarbons. successful application of bioremediation technology to contaminated soil requires knowledge of 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 poly aromatic hydrocarbons and obtain the optimized conditions of biodegradation of these pollutants in laboratory. the diversity of indigenous bacteria in four soil contaminated samples from tehran oil refinery able to degrade multiple poly aromatic hydrocarbons were isolated and the physico-chemical conditions of poly aromatic hydrocarbons biodegradation were optimized by using various concentration of the pollutants and changing ph, temperature and nutrients. the results showed that, the best conditions for efficient removal of poly aromatic hydrocarbons are; ph 7.5, temperature 30 ?c, and ratio of c: n: p 100:5:1, 100:10:1, and 100:5:1 for nh4no3, (nh4)2so4, (nh2)2co as source of n, respectively. finally, we carried out three treatments with a control to compare natural attenuation, biostimulation and bioaugmentation for poly aromatic hydrocarbons degradation in soil. after 4 weeks of incubation, bioaugmentation of the contaminated soil showed the highest percentage of biodegradation of total poly aromatic hydrocarbons (70.5%). based on the result of this study, it was concluded that, increasing in the incubation time increased the amount of the degradation of pahs and microbial population. bioremediation is an effective method of cleaning up petroleum hydrocarbons and similar studies should be carried out to isolate the native microorganisms in other oil refinery in natural conditions.