Integrated thermal and biostimulant enhanced bioremediation of PAHs and arsenic co-contaminated soil by an indigenous microbial consortium: Performance, mechanisms and limitations

Polycyclic aromatic hydrocarbons (PAHs) and arsenic (As) co-contaminated soil has emerged as a significant environmental concern. In this study, the performance and underlying mechanisms of integrated thermal and biostimulant enhanced bioremediation (ITBEB) of PAHs and As co-contaminated soil by an indigenous microbial consortium were explored. The results demonstrated that thermal treatment with temperatures elevated from 25°C to 55°C, in combination with biostimulants of rhamnolipids or yeast extract, improved the bioremediation efficiency of both PAHs and As. The highest bioremediation efficiency, 69.03% for total PAHs and 17.69% for As, were achieved at 55°C with the addition of yeast extract, compared to 39.85% and 8.69%, respectively, at 25°C without biostimulants. During the ITBEB process, the indigenous microbial consortium was capable of simultaneously degrading PAHs and transforming inorganic As into less toxic volatile forms via methylation. Notably, the abundance of functional bacteria, such as Bacillus , increased substantially from 8.29% initially to 63.71% at 55°C with yeast extract, contributing significantly to the enhanced bioremediation efficiency. Furthermore, the highest abundances of functional genes PAH-RHDα and arsM were observed at 35°C with biostimulants, whereas their expression declined at higher temperatures of 45°C and 55°C. This observation, combined with the results of correlation analyses, indicated that the effectiveness of bioremediation was strongly influenced by the presence of functional bacteria and their associated genes, as well as environmental factors such as iron content, pH, and soil organic matter. Overall, this study provides valuable insights into the synergistic effects of thermal treatment and biostimulants in the bioremediation of PAHs and As co-contaminated soils, offering a foundation for the development of more effective and sustainable remediation strategies.