Advanced phytoremediation using soil solarization enhanced with biosurfactant as a novel approach for sustainable remediation of contaminated land in the Niger Delta, Nigeria

This PhD research was carried out to study soil solarization integration with phytoremediation enhanced with biosurfactant as a sustainable remediation option to hydrocarbon contaminated land and to evaluate sustainability feasibility in the Niger Delta contaminated land clean-up. A pilot study showed that native C. odorata, preliminary selected from a case study site in the region, produced higher biomass than M. sativa - a proven and well established phytoremediation plant. Rhamnolipid biosurfactant significantly reduced the PAHs in all amended treatments of both plants in the pilot study. C. odorata was employed to investigate the effect of soil solarization enhanced with biosurfactant (500 mg/kg) on phytoremediation of aged PAH contaminated soil (240 mg/kg). Solarization was carried out for 28 days before introducing seedlings of C. odorata for a 84 day phytoremediation period using a 4 x 4 and 2 x 4 cells microcosm to simulate the region’s sub-tropical conditions for vegetated and un-vegetated treatments respectively. Soil solarization resulted in significant PAH reduction (p≤0.01) after the 28 days solarization period. Post-solarization significantly reduced (p≤0.01) PAHs in all solarized treatments compared to their non-solarized counterparts while biosurfactant did not contribute significantly (p≥0.05), due to possible denaturing by the relatively high soil temperatures recorded. The number of total soil/rhizosphere heterotrophic microorganisms increased in all solarized treatments but the increase was not statistically significant (p≥0.05). To ascertain the potential of phytoremediation in the region, a total of 32 stakeholder participants completed a questionnaire and five were further interviewed. The stakeholders scrutinized most of the default remediation techniques including covering with clean soil, excavation & disposal, thermal treatment (open burning) and concluded they were unsustainable, suggesting perceived sustainability and awareness of the different remediation techniques applicable or applied in the region. Phytoremediation and bioremediation were seen as the most sustainable remediation techniques due to being perceived as the least hazardous with high community acceptance. A holistic approach coupled with integrated sustainable remediation techniques of the type investigated in this study were seen as sustainable reparation to mitigate the current environmental, social and economic challenges to sustainability feasibility in remediation of contaminated land in the region. The novel and successful integration of soil solarization and phytoremediation using indigenous C. odorata as a combined techniques to treat even the most recalcitrant form of hydrocarbons-PAHs together with the technology acceptance by the local communities, open up new possibilities for a sustainable approach to remediate contaminated land in the oil rich Niger Delta region, Nigeria.