Enhanced indigenous bacteria-mediated bioremediation of aged petroleum-contaminated soil by Fenton pretreatment: Synergistic effect of soil environmental improvement and microbial community response

• Fenton pretreatment improved soil environment and TPHs bioavailability. • Microbial community response was explained under Fenton pretreatment . • Fenton pretreatment accelerated microbial community succession . • Efficient removal of TPHs was associated with the enhancement of membrane transport . • Enzyme genes related to TPHs degradation were enhanced under Fenton pretreatment. Due to the harsh soil environment and low microbial activity, the efficacy of indigenous bacteria-mediated bioremediation is often limited in aged petroleum-contaminated soils. In this study, Fenton pretreatment (H 2 O 2 : 200 ∼ 600 mmol/kg, H 2 O 2 : Fe 2+ = 100: 1) was applied to improve the aged soil environment and rebuild the microbial community to enhance subsequent bioremediation. After pretreated by 400 mmol/kg H 2 O 2 and 4 mmol/kg Fe 2+ (T2), the removal efficiency of total petroleum hydrocarbons (TPHs) was elevated to 93.27 %, equivalent to 1.96-fold of the natural attenuation (CK). Additionally, the half-life of biodegradation was shorted to 45.57 d, representing a decrease to 0.29-fold that of CK. Correlation analysis revealed a radar plot comprising five indicators, including bacterial quantification (BQ), dehydrogenase (DHA), polyphenol oxidase (PPO), permeability coefficient ( K ), and bulk density coefficient ( γ ), all of which exhibited positive correlations with TPHs degradation. Compared to CK, Fenton pretreatment increased the richness and evenness of the microbial community during incubation, thus facilitating TPHs biodegradation. Moreover, Fenton pretreatment accelerated the shift of the dominant genus in T2 from Pseudomonas (0.599) to Pseudomonas (0.258), Nocardioides (0.109), Dietzia (0.157), and Stenotrophomonas (0.120) throughout the incubation. Based on the analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG), the metabolism and enzymatic functional genes related to the biodegradation of petroleum hydrocarbons in T2 were enhanced during incubation, accounting for the high removal efficiency of TPHs. These findings demonstrated that moderate Fenton pretreatment was an effective approach to stimulate indigenous bacteria for the enhanced biodegradation of aged petroleum-contaminated soil.