Bioremediation of Diesel-Contaminated Soil: Hydrocarbon Degradation and Soil Toxicity Reduction by Constructed Bacterial Consortia

Petroleum pollution can pose a serious threat to soil health and its ecological functions. This study investigated the efficacy of bacterial treatments for bioremediation of diesel-contaminated soil under outdoor conditions for a period of 4 months. Unlike most previous studies conducted under laboratory conditions, this study applied single and multi-bacterial consortia directly into diesel-contaminated soil under outdoor conditions, evaluating both hydrocarbon degradation and soil toxicity changes. Three treatments using a single strain, a 4-strain consortium, and an 8-strain consortium were applied to 2% (v/w) diesel-contaminated soil, and their performance was compared to uncontaminated and untreated controls. Total petroleum hydrocarbon (TPH) degradation was quantified using GC-FID, and the soil toxicity was assessed using Eisenia fetida toxicity test and higher plant germination assays. As the experiment demonstrated, the multi-strain bacterial consortium (BT3) achieved the highest TPH degradation (78.3%) and demonstrated significant reduction in long-chain hydrocarbon fractions (C14-C28). Toxicity measurements showed that all three bioremediation treatments, especially BT3, significantly increased earthworm survival, body weight change and plant germination rate after the bioremediation. Microbial community analysis based on 16S rRNA sequencing revealed significant shifts in the dominant bacterial genera over time, accompanied by a noticeable reduction in alpha diversity. In particular, BT3 showed a significant decrease in Shannon diversity index values from 9.4 at S1 to 6.9 at S3 (p < 0.01), whereas BT1 and BT2 remained relatively stable (p > 0.05). Overall, the results demonstrated that all three bacterial treatments significantly enhanced diesel degradation and reduced soil toxicity under outdoor conditions, highlighting their potential for future large-scale applications in sustainable soil remediation. Importantly, this study combines constructed microbial consortia with multi-level toxicity assessments, providing a comprehensive framework to guide future bioremediation strategies.