Biodegradation of petroleum industry oily-sludge using Jordanian oil refinery contaminated soil

The main objective of this study was to evaluate the effect of oily sludge concentration on its biodegradability in soil. Oily sludge was collected and applied to microcosms at full-, half-, or quarter-strength concentrations equivalent to 44.2, 22.2, and 11.1 g kg^?1 soil, respectively, of total petroleum hydrocarbons (TPH) contained in oily sludge. The biodegradability of oily sludge was evaluated by measuring CO₂ evolution and by measuring removal of TPH as well as its main composing fractions; namely; alkanes, aromatics, NSO-compounds, and asphaltenes. The collected soil contained 3.63 × 10⁶ cfu g^?1 soil of hydrocarbon-degrading bacteria, which is satisfactory to drive successful biodegradation of hydrocarbons in soil. These numbers increased significantly with oily sludge addition at a rate proportional to the added TPH reaching 3.35 × 10⁷ cfu g^?1 soil in the half-strength treatment. TPH mineralization rate followed the same pattern. However, TPH-mineralization efficiency was the greatest in quarter-strength treatment at 18.3%. TPH-removal efficiency was also highest in quarter-strength treatment at 30.9%. Nutrients addition caused mineralization inhibition. Since nutrients were added as a ratio of the added carbon, inhibition was the greatest with the highest TPH treatment. While alkanes were degraded, aromatics and asphaltenes were not, and NSO-compounds were enriched. Although SDS was completely biodegradable in soil, its addition promoted mineralization and removal of TPH from soil.