Enhanced bioremediation of crude oil contaminated soil in Oleh, Delta State, Nigeria

Abstract

Crude oil pollution of soils is an ongoing challenge in the Niger Delta region of Nigeria, resulting in decreased farmlands with the overall threat to food and nutrition security, as well as human health. Thus, bioremediation suited for organic pollutants should assume priority in addressing this enormous challenge. Therefore, this study investigated the efficacy of Remediation-By-Enhanced-Natural-Attenuation (RENA) method in remediating crude oil contaminated soil in Oleh, Delta State, Nigeria. Remediation-by-enhanced-natural-attenuation was performed on a crude oil contaminated plot. Soil samples (0-20 cm) were collected at pre-remediation, one and three weeks remediation periods to determine Total Petroleum Hydrocarbon (TPH), Polycyclic Aromatic Hydrocarbon (PAH), microbial counts, nutrients and heavy metals. Pre-remediation TPH concentration (mg/kg) of 274.84±0.81 significantly reduced to 195±1.6 after three weeks. Similarly, there was a gradual decrease (36%) in PAH concentrations during the remediation period. Naphthalene and related compounds (possible carcinogens) accounted for over 50% of PAH in pre-remediation soil. The concentrations of Ni, Cr, Cd, and Zn decreased significantly at the end of the study. Hydrocarbon utilising bacteria peaked at 2.38±0.06 (cfu/g×102) in week one but reduced to 1.12±0.07 (cfu/g×102) in week three. Total fungi peaked (1.75±0.04 cfu/g ×104) at week three remediation period while the hydrocarbon utilising fungi peaked (1.16±0.06 cfu/g×102) at week one remediation period. The study demonstrated that remediation-by-enhanced-natural-attenuation significantly increased indigenous hydrocarbon utilising species, with a significant reduction in TPH, PAH and heavy metals concentrations after 3-week remediation period. Our study further confirms the practicability of RENA in reclaiming crude oil contaminated soil in Nigeria.