Evaluation of biostimulation, bioaugmentation, and organic amendments application on the bioremediation of recalcitrant hydrocarbons of soil

In the present work, the operational conditions for improving the degradation rates of Total Petroleum Hy-drocarbons (TPHs) in contaminated soil from a machinery park were optimized at a microcosms scale along a 90 -days incubation period. In this study, bioremediation strategies and an organic amendment have been tested to verify the remediation of soil contaminated with different hydrocarbons, mineral oils, and heavy metals. Spe-cifically, designed biostimulation and bioaugmentation strategies were compared with and without adding vermicompost. The polluted soil harboring multiple contaminants, partially attenuated for years, was used. The initial profile showed enrichment in heavy linear alkanes, suggesting a previous moderate weathering. The application of vermicompost increased five and two times the amounts of available phosphorus (P) and exchangeable potassium (K), respectively, as a direct consequence of the organic amendment addition. The microbial activity increased due to soil acidification, which influenced the solubility of P and other micro -nutrients. It also impacted the predominance and variability of the different microbial groups and the incubation, as reflected by phospholipid fatty acid (PLFA) results. An increase in the alkaline phosphatases and proteases linked to bacterial growth was displayed. This stimulation of microbial metabolism correlated with the degra-dation rates since TPHs degradation' efficiency after vermicompost addition reached 32.5% and 34.4% of the initial hydrocarbon levels for biostimulation and bioaugmentation, respectively. Although Polycyclic Aromatic Hydrocarbons (PAHs) were less abundant in this soil, results also decreased, especially for the most abundant, the phenanthrene. Despite improving the degradation rates, results revealed that recalcitrant and hydrophobic pe-troleum compounds remained unchanged, indicating that mobility, linked to bioavailability, probably represents the limiting step for further soil recovery.

Automated summary

This study optimized the degradation rates of TPHs in contaminated soil by using biostimulation and bioaugmentation strategies with the addition of vermicompost. The results showed that vermicompost increased nutrient levels in the soil, enhanced microbial activity, and improved degradation efficiency.