Enhanced Heavy Metal Removal from Synthetic Stormwater Using Nanoscale Zerovalent Iron-Modified Biochar

The use of biochar for removal of heavy metals from stormwater is limited due to large area requirements and inadequate removal of nutrients and heavy metals at higher initial concentrations. In this study, biochar-supported nanoscale zerovalent iron (BC-nZVI) was effectively utilized for removing heavy metals from synthetic stormwater. We performed batch adsorption and laboratory-scale column experiments to demonstrate the exceptional ability of BC-nZVI to remove heavy metals (Cu, Cd, and Zn) at varying higher initial concentration range (2.5 to 60 mg L-1) compared with typical urban stormwater runoff. The batch experiment results suggested that the metal removal efficiency of BC-nZVI compared with biochar was enhanced by 43% and 57% in individual metal solution and 50% and 42% in the mixed metal solution for Cd and Zn, respectively. The maximum adsorption capacities of BC-nZVI for individual metal ions increased by 97% and 40% for Cd2+ and Zn2+, respectively, compared with original biochar. A series of characterization studies based on scanning electron microscopy, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller revealed the chemical and morphological features of BC-nZVI, which are responsible for the enhanced metal removal. A laboratory-scale column study mimicking the field scale revealed the metal removal efficiencies of BC-nZVI increased by 115% and 123% for Cd2+ and Zn2+, respectively, compared with unmodified biochar. The higher removal efficiencies and adsorption capacities demonstrate the potential use of BC-nZVI as a media for attenuating heavy metals in current stormwater management practices.