Sulfurized bimetallic biochar as adsorbent and catalyst for selective co-removal of cadmium and PAHs from soil washing effluents

Although biosurfactant enhanced soil washing is effective to remediate Polycyclic Aromatic Hydrocarbons (PAHs)-Heavy metals (HMs) co-contaminated soil, the treatment of soil washing effluents containing pollutant and biosurfactant remains a critical challenge. In this study, the sulfurized Fe-Mn bimetallic biochar, named FMSBC was prepared, which exhibited excellent performance in activating sodium percarbonate (SPC) to degrade phenanthrene and the good adsorption capacity of cadmium. A simple system using FMSBC adsorption and SPC oxidation (FMSBC/SPC) is thus developed to remove phenanthrene and cadmium from soil washing effluents. Although there was antagonistic behavior between PAHs and HMs in the FMSBC/SPC system, over 80% phenanthrene and cadmium can be simultaneously removed from soil washing effluents. Adsorption of cadmium was mainly driven by complexation and precipitation. Free radical quenching studies and electron paramagnetic resonance (EPR) analyses verified that the dominant radical in the FMSBC/SPC system was hydroxyl radical (·OH). The performances of adsorption and catalyst were stable across a wide pH range and in the presence of competitive metal ions or natural organic matters. The recovered biosurfactants could be further reused for three washing cycles. This study has suggested biosurfactant enhanced soil washing coupled with FMSBC/SPC system is a promising method for remediation of HMs-PAHs co-contaminated soil.