Bioremediation of petroleum hydrocarbons by vermicomposting process bioaugmentated with indigenous bacterial consortium isolated from petroleum oily sludge.

Finding a sound ecological-based approach for the removal of petroleum hydrocarbons (PHCs) from petroleum oily sludge (POS) generated in oil refinery plants is still a challenge. This study investigated the removal of total petroleum hydrocarbons (TPHs) using bioaugmentated composting (BC) by hydrocarbon-degrading bacteria (HDB) and vermicomposting (VC) by Eisenia fetida, individually and in combination (BCVC). After isolating two native bacterial strains from POS prepared from an oil refinery plant in Iran, the degradation capability of their consortium was initially assessed in mineral Bushnell-Haas medium (MBHM). Then, the biodegradation rates of POS in the BC, VC, and BCVC treatments containing different concentrations of TPHs (5, 10, and 20 g/kg) were determined by measuring TPHs before and after the biodegradation. The results showed that the consortium degraded 20-62% of TPHs contents of Kerosene (1-5%) in the MBHM after 7 days. After 12 weeks, the TPHs removal percentages in the BC, VC, and BCVC treatments were respectively found to be 81-83, 31-49, and 85-91 indicating the synergistic effect of bacteria and worms in bioremediation of POS. The PHCs biodegradation in the BC, VC, and BCVC experiments was fitted to 1st order model kinetics. The results of toxicity tests indicated that the values of the no observed lethal concentration (NOLC) and median lethal concentration (LC50) of TPHs were 2-5 and 14.64 g/kg, respectively after 28 days of earthworm exposure. Morphological impairments such as swelling, coiling, and curling were observed when TPHs concentration was even lower than NOLC. The study verified the effectiveness of vermicomposting bioaugmentated with the indigenous bacterial consortium for POS bioremediation.

Propositure of maximum permissible limits for environmental assessment and classification of materials stabilized by solidification incorporated with oil waste.

In the present work, oil sludge was subjected to the process of stabilization by solidification, the objective was to indicate maximum permissible limits of chemical demand for oxygen and oils and greases to evaluate the resulting material. A factorial design was used with the addition of three repetitions at the central point, to evaluate the performance of different percentage of residue and different curing times. The factors adopted were the percentage of oil sludge and the curing time. This material was evaluated using contaminants immobilization tests. From the leached and solubilized liquid, the concentration of the contaminants was determined and the environmental assessment was also carried out through the analysis of chemical demand for oxygen and oils and greases. One of the contributions of this work was to propose the maximum allowable limit for chemical oxygen demand, which is 1,000 (one thousand) milligrams per litre and, for oil and grease content, 100 (one hundred) milligrams per litre, both for the leaching test. For the solubilization test, 10 (ten) milligrams per litre were proposed for chemical oxygen demand and 1 (one) milligrams per litre for the oil and grease content. It was observed that the best results are obtained, when lower values of percentage of oil sludge were used and longer cure time. This work allows to affirm that the proposal of limits of environmental evaluation contributes to assure an adequate disposition and use of the cement matrix, that is the final product of the oily residue stabilized by solidification.