Comparison of phytoremediation, bioaugmentation and natural attenuation for remediating saline soil contaminated by heavy crude oil

• Bioaugmentation with a halotolerant microbial consortium had a fast startup.
• Phytoremediation with tall fescue had a higher TPH removal efficiency at the end.
• Increase in ring number and alkyl substitution of PAH and SCH leads to decrease in degradation rate.

Bench-scale pot culture systems were used to investigate the effectiveness of phytoremediation (Testuca arundinacea), bioaugmentation (5 oil-degrading strains), and natural attenuation for remediating saline soil contaminated by Venezuela heavy crude oil. GC–MS was used to have a comparative characterization for chemical composition changes of aromatic groups (polycyclic aromatic hydrocarbons (PAHs), sulfur-containing heterocycles (SCHs) or polycyclic aromatic sulfur heterocycles (PASHs), and aromatic biomarkers) during different remediation processes. Bioaugmentation had faster startup (higher total petroleum hydrocarbon (TPH) removal efficiency on Day 30) while phytoremediation had higher TPH removal efficiency at the end of experiments (90 days). The 90-day TPH removal efficiency of phytoremediation (64.0 ± 1.6%) was significantly higher (p < 0.05) than that of bioaugmentation (54.6 ± 1.3%) which was significantly higher (p < 0.05) than that of natural attenuation (20.7 ± 2.8%). GC–MS analysis shows that the removal efficiencies of most of individual PAH and SCH compounds by phytoremediation were also significantly higher (p < 0.05) than bioaugmentation which were significantly higher (p < 0.05) than natural attenuation. GC–MS analysis also shows that the removal efficiencies of individual PAH and SCH compounds for all three treatments (phytoremediation, bioaugmentation, and natural attenuation) decreased with increases in ring number and degree of alkyl substitution. Overall, this study shows that phytoremediation with T. arundinacea and bioaugmentation with a halotolerant microbial consortium are two effective approaches for remediating saline soil contaminated by heavy crude oil.

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