Abstract
Khuzestan province accommodates the largest oil-fields with huge petroleum production in Iran. Oil spills through transportations, oil pumping station and storage tanks are the cause of frequent contamination in land areas, including crop fields, imposing great damages to soil ecology. Thus, oil removal from contaminated soil by advance technologies such as bioremediation seems to be of vital necessity. The aim of this work was to study the effect of agricultural fertilizers and sewage-sludge application on bioremediation of oil-contaminated soil. Soil samples (5kg) were artificially contaminated with crude oil to a level of 1%. Fertilizers treatments were applied in 3 levels of 0, 1 and 2 ton/ha in 3 replicates. The soils were kept in normal moisture aerobic environment for 5 and 10 weeks. The soils were then analyzed for hydrocarbon-degrading heterotrophic bacteria count. Oil degradation was measured by oil Soxhlet extraction method. The results showed that the hydrocarbon-degrading and heterotrophic bacteria count in all the treatment increased with time. The result showed that hetrotrophic bacteria population increased from 6×103 cfu/gr soil to 1.4×108 cfu/gr soil Also, C/N Ratio decreased from 6 to 3. GC results indicated that all normal paraffin and isopernoids i.e. Phytane and Pristane decreased from 50 to 90 percent in all treatments moreover, the result indicated that application of fertilizers in 2 ton/ha rate in oil-contaminated soil lead to greater rates of biodegradation after 5 weeks, and could be introduced as the best suggested condition. Rates of biodegradation after 5 weeks.

Key words: Bioremediation, hetrotrophic bacteria, Gas Chromatography, Normal paraffin