Study on Amendment of Rapeseed Meal, Soybean Meal, and NPK Fertilizer as Biostimulants in Bioremediation of Diesel-Contaminated Soil by Autochthonous Microorganisms

Abstract

ABSTRACT The adverse impact of total petroleum hydrocarbons (TPH) can be mitigated through bioremediation. However, the efficiency of bioremediation is often compromised due to its slow speed. Therefore, this study aimed to evaluate the promoting effect of organic and inorganic biostimulants on the bioremediation rate of autochthonous microorganisms. The study examined the impact of rapeseed meal (biostimulation-BS1), soybean meal (BS2), and NPK fertilizer (BS3), as biostimulants on pH, bacterial and fungal count, enzymatic activities, and also TPH values of diesel-contaminated soil. The results revealed that amending the soil with rapeseed meal, soybean meal, and NPK fertilizer resulted in a significant increase in dehydrogenase and catalase activities, with 9.96, 7.7, and 6.75-fold and 2.52, 2.4, and 2.52-fold enhancement, respectively, compared to natural attenuation (NA-as control) which contains diesel-contaminated soil without any organic or inorganic amendments. Moreover, the pH value of the BS1 (6.4) and BS2 (6.77) groups was almost neutral. The growth of heterotrophic and hydrocarbon-utilizing bacteria and fungi was significantly improved with organic matter amendment (P < .05). The TPH removal efficiencies in natural attenuation, BS1, BS2, BS3, and rapeseed meal+ soybean meal+ NPK fertilizer (BS4) groups were 49.22%, 71.65%, 90.55%, 65.77%, and 55.25%, respectively. Molecular identification revealed that three hydrocarbon-utilizing bacteria belonged to various genera, including Nocardiopsis, Streptomyces, and Mammaliicoccus. Overall, this study suggests that amending organic compounds to contaminated soil is an effective, cost-effective, and eco-friendly strategy to improve the bioremediation rate of autochthonous microorganisms.