Co-application of phytoremediation with iron-loaded biochar in petroleum and zinc co-contaminated soil

Phytoremediation, a proven technique widely used in soil remediation, encounters challenges in addressing the synergistic effect of petroleum and heavy metals in co-contaminated soils. Enhancing phytoremediation with modified biochar could improve its effectiveness, but the remediation mechanism of pollutants and the structure of microbial communities in soil aggregates have rarely been studied. Ferrate-modified biochar (FeBC) was used in this study to promote the phytoremediation of petroleum and zinc co-contaminated soils. Results showed that ferrate significantly enhanced the microstructure, elemental composition, and surface crystal composition of pristine biochar. The co-remediation by FeBC and ryegrass significantly improved the removal of petroleum hydrocarbons in soil, especially in meso-aggregates. Simultaneously, the bioavailability of zinc in the soil was reduced by FeBC, contributing to the less accumulation of zinc in ryegrass. The interactions among FeBC, soil aggregates and ryegrass indicated that FeBC enhanced the plant resistance by the formation of iron membranes on the surface of ryegrass roots, and enriched dissolved organic matters in meso- and micro-aggregates. The addition of FeBC resulted in the increase of urease and alkaline phosphatase activities in the rhizosphere soil of ryegrass. Furthermore, the application of FeBC led to a notable increase in the content of phospholipid fatty acids in the ryegrass rhizosphere soil, particularly in bacterial populations within the soil meso- and micro-aggregates fractions. The bacterial communities with more cooperative relationship and greater stability were reshaped in different soil aggregate structures by the FeBC addition. This study delves into the potential mechanism of co-remediation by exploring the interactions among ferrate-modified biochar, rhizosphere microbial community and soil aggregates, providing innovative insights into the phytoremediation of soil contaminated by petroleum and zinc.