Biochar mediates activation of aged nanoscale ZVI by Shewanella putrefaciens CN32 to enhance the degradation of Pentachlorophenol

The bioreduction of aged nanoscale zero valent iron (NZVI) by Shewanella putrefaciens CN32 (CN32) in the presence of different biochar materials was conducted to understand how biochars mediated the activation of aged NZVI to enhance the removal efficiency of contaminants. The results indicated that the prepared biochars contained different oxygen-containing functional groups (such as -O-C=O, -COOH, C=O, C-O, C-C, C-H and C=C). The biochars significantly enhance electron transfer from CN32 to aged NZVI, thus accelerating reductive dechlorination of Pentachlorophenol (PCP). The maximum PCP degradation rate (k(max)) was 2.45 mg.L-1.d(-1), which was 2.6 times greater than that of the biochar-free control (0.94 mg.L-1.d(-1)). The intermediates of phenol were detected after 30 days, likely indicating that reductive dechlorination was the dechlorination pathway of PCP. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis showed that vivianite, as a secondary mineral, was formed during the bioreduction aged NZVI-BC600 (Biochar prepared at 600 degrees C with NZVI activation) by CN32. Vivianite was formed mainly through the reaction of Fe(II) and PO43-. The combined electrochemical and electron paramagnetic resonance analysis might suggest that biochar associated semiquinone radical (C=O) were likely involved in the bioreduction of aged NZVI. This study provided some theoretical support for further research on biochar mediated bioreduction activation of aged NZVI to enhance the degradation of contaminants.