Ferrihydrite redox enhanced biodegradation of petroleum hydrocarbons coupling with conversion of soil multi-elements by electron transfer.

In the soil microbial electrochemical remediation, iron transformations commonly govern electron transfer, bioelectricity generation and pollutant degradation. In this study, the conversion of ferrihydrite to goethite (cathode) and hematite (anode) increased electronic circulation channels, with a 67 % increase in charge output and 74 % improvement in petroleum hydrocarbon removal. Simultaneously, ferrihydrite-mediated processes facilitated the activation of recalcitrant organic carbon, resulting in 9 % lignin and 30 % unsaturated hydrocarbon degradation. This transformation shifted organic matter composition toward lower aromaticity and higher reduction potential. Concurrently, introduced-ferrihydrite significantly restructured the microbial community by enriching Desulfuromonas and Pseudomonas, leading to a more complex co-occurrence network, improving the coupled electron transfer and pollutant degradation. Furthermore, ferrihydrite played a regulatory role in the iron cycle with transforming genes upregulating by 171 %, driving coupled biogeochemical transformations. Consequently, processes of denitrification, sulfate reduction and inorganic phosphorus release were enhanced in terms of corresponding genes upregulated by 90 %, 15 % and 40 %, respectively. All these processes were synergistically associated with carbon metabolism with functional genes upregulating by 50 %. In conclusion, ferrihydrite exhibits both electron-mediated and carbon-activated functionalities, thereby providing a support for the remediation of organic contaminated soil as well as the directional regulation of nutrient elements transformation.