Advanced Journal of Environmental Science and Technology

Advanced Journal of Environmental Science and Technology ISSN 7675-1686 Vol. 11 (3), pp. 001-010, March, 2020. © International Scholars Journals

Full Length Research Paper

Bioremediation of hydrocarbon contaminated-oil field drill-cuttings with bacterial isolates

Reuben N. Okparanma*, Josiah M. Ayotamuno and Peremelade P. Araka

Department of Agricultural and Environmental Engineering, Rivers State University of Science and Technology, Port Harcourt, P.M.B 5080, Rivers State, Nigeria.

Accepted 16 May, 2019

Abstract

The effectiveness of 2 bacterial isolates (Bacillus subtilis and Pseudomonas aeruginosa) in the restoration of oil-field drill-cuttings contaminated with polycyclic aromatic hydrocarbons (PAHs) was studied. A mixture of 4 kg of the drill-cuttings and 0.67 kg of top-soil were charged into triplicate plastic reactors labeled A1 to A3, B1 to B3, C1 to C3 and O1 to O3. These were left quiescent for 7 days under ambient conditions before adding to reactors A1 - A3 and B1 - B3 respectively, 20 ml working solution of pure cultures of Bacillus sp and Pseudomonas sp each of cell density 7.6 x 10¹¹ cfu/ml. Another 20 ml working solution containing the both cultures at cell density 1.5 x 10¹² cfu/ml was added to reactors C1 - C3. The working solution was added to each reactor (excluding the controls, O1 - O3) every 2 weeks mixing and watering of the set-ups was done at 3 days interval under ambient temperature of 30^oC over a period of 6 weeks. After 6 weeks of treatment, results showed that the predominant 3-ring PAHs, which made up 90% w/w, of the total PAHs concentration of 223.52 mg/kg, were degraded below detection and the 4-ring PAHs were reduced from 4 to 0.6% by the Pseudomonas while the Bacillus reduced the 3 and 4-ring PAHs respectively to 0.2 and 0.8%. This showed that the Pseudomonas degraded the 3 and 4-ring PAHs relatively better than the Bacillus. Both strains of bacteria degraded the 5 and 6-ring PAHs below detection limits. Furthermore, within the 3-ring PAHs each of the strains of bacteria reduced phenanthrene to approximately 0.2%, whereas both degraded the homologues acenaphthylene, acenaphthene and fluorene as well as anthracene below detection limits. For the 4-ring PAHs, the Pseudomonas degraded fluoranthene and benzo[a]anthracene while the Bacillus also degraded benzo[a]anthracene below detection limits. The Pseudomonas was able to reduce pyrene and chrysene to 0.3 and 0.2% respectively; whereas the Bacillus reduced fluoranthene, pyrene and chrysene to 0.1, 0.01 and 0.4% respectively. However, treatment with the mixed culture resulted in the limited degradation of the 5-ring PAHs particularly in the fourth week, which may be due to the phenomena of cometabolism and inhibition. The pseudo-first-order degradation rate constant of persistent PAHs ranged from 1.9 x 10^-4 to 9.3 x 10^-2 day^-1. Statistical analyses of results, using the 2-factor analysis-of-variance, showed that the treatments applied resulted in significant (p < 0.05) differences in the biodegradation of the PAHs of the drill cuttings after the 6 weeks of treatment.

Key words: Polycyclic aromatic hydrocarbons, petroleum waste, Bacillus, Pseudomonas, bioremediation.