In the present work, the operational conditions for improving the degradation rates of Total Petroleum Hydrocarbons (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. Specifically, 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 micronutrients. 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 degradation 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 petroleum compounds remained unchanged, indicating that mobility, linked to bioavailability, probably represents
the limiting step for further soil recovery.
