Abstract
Hydrocarbon-contaminated land has been a significant issue throughout Nigeria's Niger Delta since the discovery of crude oil in 1956. This paper proposes a novel and sustainable technique involving soil solarization, phytoremediation and biosurfactant to treat polycyclic aromatic hydrocarbon (PAH) contamination. The treatment effect on PAH reduction, plant growth, rhizosphere microorganisms and their enzymatic activities was evaluated. Twenty-eight days of solarization was carried out before the introduction of Chromolaena odorata seedlings for an 84-day phytoremediation period using a 4 × 4 (vegetated) and 2 × 4 (non-vegetated) cell microcosms to simulate the Niger Delta's subtropical conditions. Soil solarization resulted in significant PAH reduction (p ≤ 0.01) of phenanthrene, fluoranthene and benzo(a)pyrene with means reduction of 60.0%, 38.7% and 36.1% compared to their non-solarized counterparts with 18.0%, 18.0% and 18.8% at 95% CI (32.7, 51.3), (15.4, 26.1) and (8.0, 26.6), respectively. In post-solarization, all solarized and vegetated treatment groups significantly reduced (p ≤ 0.01) PAHs compared to their respective counterparts, while biosurfactant contribution in this combination was negligible (p ≥ 0.05). The growth parameters of C. odorata, total soil/rhizosphere heterotrophic microorganisms and their enzymatic activities of dehydrogenase and urease increased in all solarized treatments indicating essential biochemical processes. The novel and successful integration of soil solarization and phytoremediation using indigenous C. odorata as a combined technique to treat even the most recalcitrant form of hydrocarbons (PAHs) brings up new opportunities for a sustainable method of cleaning up contaminated land in Nigeria's oil-rich Niger Delta.