Biochar assisted bioremediation of soils with combined contamination of petroleum hydrocarbons and heavy metals: A review

Contaminants in soils tend to be complex, with the combination of petroleum hydrocarbons (PHs) and heavy metals (HMs) being of particular concern. Bioremediation, using plants and associated microorganisms, is considered one of the most promising technologies for the removal of PHs and HMs from soils. However, the remediation efficiency of bioremediation is limited by microbial activity, plant growth behavior and soil property. Fortunately, biochar, as a cost-effective and environmentally friendly soil amendment, shows great promise in the removal of PHs and the immobilization of HMs. This study first reviewed the current situation of combined pollutions of PHs and HMs in soils. It then reviewed the application of biochar enhanced the bioremediation efficiency in the remediation of PHs-HMs co-contaminated soils, and highlighted the key genes involved in the remediation of these two pollutants and revealed the mechanism of remediation of soil co-contaminated with PHs and HMs at the molecular biology level. In addition, the current research results of biochar-assisted bioremediation were summarized and the reasonable mechanisms of biochar-assisted bioremediation of PHs-HMs contamination were illustrated. Finally, the challenges and future perspectives of biochar in enhancing bioremediation were discussed, and the remediation strategies of PHs-HMs co-contaminated soils through integration of phytoremediation, degrading microorganisms and biochar were proposed. This research has positive implications for improving soil health and managing combined contaminated soils.