Microbial degradation of nondesorbable organic compounds on biochars by extracellular reactive oxygen species

Knowledge of microbial degradation of biochar-adsorbed organic pollutants is essential for recovering adsorption performance of biochars and reducing secondary pollution in soil remediation. In previous study, desorption of organic compounds from biochars was perceived as a prerequisite for the microbial degradation. However, microbial degradation of the nondesorbable organic compounds on biochars has not been studied. Therefore, degradation of nondesorbable naphthalene (NAPH), phenanthrene (PHEN) and pyrene (PYR) on a wood chip-derived biochar (WBC700) by Sphingobium yanoikuyae B1 was investigated. Significant microbial degradations of nondesorbable organic compounds were observed and followed the order of NAPH < PHEN < PYR. It was newly observed in this study that the microbial degradation of nondesorbable organic compounds on WBC700 was mainly attributed to the •OH in extracellular fluid of Sphingobium yanoikuyae B1. The extracellular •OH was produced through a Fenton-like reaction involved siderophore, H₂O₂ and iron ions, which could be significantly enhanced by WBC700. Microbial degradation was higher for larger organic compound (e.g., PYR), because larger molecules were adsorbed in relatively larger micropores of WBC700 and thus could be accessible to more extracellular •OH for degradation. The obtained results could provide a new insight into the microbial degradation of biochar-adsorbed organic pollutants in soil remediation.