Khuzestan Province accommodates the largest oil-fields with huge petroleum production in Iran. During the Persian Gulf war in 1991, more than 6-8 million gallons of oil was spilt in the Persian Gulf, the greatest amount of which was transported into Khuzestan soil. Thus, oil removal from contaminated soil by advanced technologies such as bioremediation seems to be of vital necessity. The aim of this study was to evaluate the effect of sewage-sludge application on bioremediation of oil-contaminated soil. Soil samples (5kg) were artificially contaminated with crude oil to a level of 1000 mg/kg. Sewage sludge treatments were applied at the 3 levels of 0, 100, and 200 gr/5kg soil in 3 replicates. The soils were kept in the normal moisture aerobic < JU olji (5JJ C^J ^^k- ^ J C^lgjy .JLt j yajkj* ji
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environment for 5 and 10 weeks. The soils were then analyzed for Hydrocarbon-degrading heterotrophic bacterial count. Oil extraction from the samples was accomplished using the oil Soxhlet extraction method and oil degradation was measured by GC chromatography. The results showed that the hydrocarbon-degrading and heterotrophic bacterial counts in all the treatments increased with time. Results indicate that heterotrophic bacterial population increased from 6><10 cfu/gr soil to 2><1010 cfu/gr soil. Also, C/N ratio decreased from 6 to 3. GC results indicated that all normal Alkanes and Isopernoids, i.e. Phytane and Pristane, decreased by 50-90 percent in all the treatments. It was also found that the application of sewage sludge at 100 gr/5kg soil to oil- contaminated soil leads to greater rates of biodegradation after 5 weeks
