Bioremediation of a crude oil contaminated soil using water lettuce (<i>Pistia stratiotes</i>)

Abstract

Laboratory-scale studies were carried out using a nutrient formula produced from Pistia stratiotes plant to achieve bioremediation of crude oil impacted loamy soil. This study assessed the efficacy of powdered Pistia stratiotes as potential bio stimulant in the remediation of crude oil contaminated soil using three test treatments (20ml, 60ml and 100ml) at three test concentrations (20g, 40g and 60g) of nutrient and a control (0g). The remediation process was monitored by assaying the total hydrocarbon content (THC) and soil pH before and after amendment with the powdered P. stratiotes for 90 days. The result showed increase in soil pH and THC in comparison with the control due to soil contamination by crude oil. However, there was a significant reduction (p < 0.05) in soil pH and THC with the introduction of powdered P. stratiotes at different concentrations. Contaminated soil amended with 40g of P. stratiotes had the highest THC loss of (30%) on the final day of remediation. In a 90 day study, the control set-up had its total culturable heterotrophic bacterial population of the P. stratiotes recipe increase from 1.4×10⁷ Cfu/g to 2.8×10⁷ Cfu/g, while the total culturable heterotrophic fungal count in the P. stratiotes treatment ranged from 7.0×10⁴ Cfu/g to 4.0×10⁴ Cfu/g. Statistical analyses showed significant difference at p ≤ 0.05 level for the two conditions (Pistia stratiotes nutrient treated soil and control). The total culturable hydrocarbon utilizing bacteria in P. stratiotes treated polluted soil increased from 1.0×106 Cfu/g to 6.8×105 Cfu/g, while the total culturable hydrocarbon utilising fungal counts increased significantly from 1.9×10⁴ Cfu/g to 4.8×10⁴ Cfu/g for P. stratiotes treatment. The results from this research demonstrated that powdered P. stratiotes is an effective agent that can be used to decrease the pH of contaminated soil and improve soil properties, hence aids in remediating a crude oil contaminated soil.