Ex-situ bioremediation of petroleum hydrocarbon contaminated soil using mixed stimulants: Response and dynamics of bacterial community and phytotoxicity

Pollution of agricultural soils by excessive petroleum hydrocarbons (PHs) has recently become a severe world-wide environmental issue. Various approaches have been recently employed to biodegrade PHs and detoxify soils. In the present study, an experimental mesocosm was developed in a bioslurry reactor. Six treatments were applied to degrade PHs-and detoxify contaminated soil by adding external stimulants such as nutrients, activated sludge, synthetic surfactant, and long-chain rhamnolipids. The comparative analysis revealed that the combi-nation of activated sludge, nutrients, and biosurfactant showed a 79.4% reduction in TPHs after 10 days in the mesocosm experiment. The lowest reduction in total PHs (48.5 %) was attained in the nutrient-supplied meso-cosms. The consortia's kinetic analyses of PHs revealed the lowest half-life time (t1/2 = 4.1 days), the highest biodegradation rate constants (k = 0.17 day1), and the reaction rate data from each bioremediation method was fitted with a first-order reaction rate model. The 16S rRNA gene amplicon and sequencing revealed that Strep-tomyces, Nocardioides, Arthrobacter, Pseudomonas, and Bacillus were the main oxidative species as PHs degraders. The highest relative abundances were in Arthrobacter, Pseudomonas, and Bacillus. The phytotoxicity studies proved that there was a significant decrease in the toxicity of soil after the biotreatment. According to the findings of this study, adding external stimulants such as activated sludge, nutrients, and biosurfactants enhanced the degradation of PHs in the soil in bioslurry enhancement as a promising approach to pilot scale.