The Biodegradation of Petroleum Hydrocarbons from Crude Oil-contaminated Soil by White-Rot Fungi

Abstract

Soil pollution by petroleum hydrocarbons is a major environmental concern. Due to the magnitude of this problem and the lack of a practical solution, an efficient and economical alternative is needed. Fungal bioremediation may be an ideal solution to this problem, especially since fungi can withstand organopollutant levels which are already toxic to most organisms. Two fungal strains - Phanerochaete chrysosporium FCUP 644 and Pleurotus ostreatus FCUP 499 were used referring on their previously confirmed ability to degrade a wide variety of organopollutants. Only one fungal isolate for the main biodegradation experiment was selected, based on its tolerance to high crude oil concentrations and its ability to produce relatively dense mycelia. A sensitivity study to petroleum hydrocarbons was performed by growing each fungal strain in malt extract agar plates spiked with increasing concentrations of crude oil. Crude oil tolerance was inferred from the growth rate of the fungi in crude-oil contaminated malt extract agar plates. The sensitivity study revealed that both strains can sustain growth in crude oil concentrations of up to 20,000 ppm, indicating a high tolerance to petroleum hydrocarbons. Ph. chrysosporium FCUP 644 displayed a greater rate of mycelial extension, but visual analysis revealed that Pl. ostreatus FCUP 499 had denser mycelia. For the main biodegradation experiment, a denser mycelium was favored because of the extracellular nature of fungal enzymatic activity. Hence, Pl. ostreatus FCUP 499 was used in the main biodegradation experiment for its high tolerance to petroleum hydrocarbons and greater mycelial density. To provide nutrition for the growing fungi in the main biodegradation experiment, a bulking agent composed of bran flakes, wood shavings and a pH 6 phosphate buffer solution was prepared. In preparation for soil inoculation, the fungal strains were grown in the bulking agent for 23 days. To keep growth conditions controlled, the incubation of both treatment groups was performed in bioreactors with identical contents. The control batches contained a mixture of the oil-contaminated soil and the sterile bulking agent, while the experimental batches were inoculated with Pl. ostreatus FCUP 499. After forty days of incubation, gravimetric analysis via Soxhlet extraction showed that there is a net 17.76% hydrocarbon loss in the experimental group which can be attributed to the activity of Pl. ostreatus FCUP 499. Gas Chromatography / Mass Spectrometry analysis revealed that there is no significant difference between the removal of Total Petroleum Hydrocarbons between the control and the experimental group after incubation, suggesting that Pl. ostreatus FCUP 499 is unable to degrade these compounds.