Shift in polycyclic aromatic hydrocarbons and heavy metal concentrations of a crude oil-polluted soil undergoing laboratory-scale bioremediation

Abstract

The shift in polycyclic aromatic hydrocarbons (PAHs) and heavy metal concentrations during the laboratory-scale bioremediation of crude oil-polluted soil from the K-Dere, Ogoni land, Nigeria was studied. Crude oil-polluted soil samples were collected and processed, and bioremediation experimental treatment units were set up to monitor the changes in PAHs and heavy metal concentrations within 40 days using different treatment options. The treatment options consist of four experimental units, which include sample A (polluted soil only), sample B (polluted soil and bacterial consortium), sample C (polluted soil and NPK) and sample D (polluted soil and cow dung). PAHs were analysed using the Gas Chromatography-Flame Ionization Detection, while the heavy metals were analysed using the Atomic Absorption Spectrophotometer. There was an overall reduction in PAH and heavy metal concentrations after treatment. A PAH loss of 12.30% was recorded in sample A, 60.82% in sample B, 44.75% in sample C and 21.03% in sample D. Sample B, which had the bacterial consortium, experienced the highest PAH reduction, while sample A recorded the lowest PAH reduction. Lead, nickel and chromium concentrations recorded slight decreases of 15.20, 16.50 and 19.40%, respectively. Sample D recorded the highest reduction in zinc concentration of 32.00%, while sample B recorded the highest reduction in copper concentration on day 20. Cadmium, iron and copper concentrations significantly reduced in sample B on day 40. This study has further revealed the need to explore Indigenous bacterial consortium and other bioremediation approaches to recover PAH and heavy metal-impacted ecosystems.