Quantitative contribution of iron-char composites mediating enhanced abatement on p-nitrophenol through extracellular electron transfer

The coupling application of carbonaceous material provides an innovative strategy to improve anaerobic bioreaction in wastewater treatment. This study synthesized biomass-waste-derived iron-char composites via a co-pyrolysis to explore the role on the biotransformation of p-nitrophenol (PNP) in anaerobic systems. With the increasing temperature, the proportion of crystalline magnetite was enhanced in iron-char composites. The transformation of Fe species from inorganic to organic combined states were evidenced by C − O − Fe bond formation as per XPS spectra, which improved the electron transfer performance of carbon matrix. Quantitative calculation demonstrated that iron-char composites significantly boosted microbial PNP degradation by 34.1–55.3%, especially for iron-chars of high temperature. The mediated electron transfer capacity of iron-char composites was a critical factor enhancing anaerobic PNP degradation with increasing pyrolysis temperature. In addition, the Fe(II) released from hematite/magnetite in iron-chars was observed, which was significantly responsible for PNP degradation. This study quantified the contributions of microbial metabolism, mediated electron transfer, and interfacial reactivity to microbial transformation of nitrophenol contaminant through establishing a structure-application relationship of iron-char composites. This work provides critical scientific insights and practical guidance for the bio-augmentation treatment of nitro-phenolic industrial wastewater.