Assessment of biochar supported sulfidized iron-based nanoparticles for immobilization of cadmium in sediment: Effectiveness, contribution of iron reducing bacteria, and mechanism insight.

Biochar supported sulfidized nanoscale zerovalent iron (S-nZVI-BC) has shown great potential for environmental remediation. However, the feasibility of S-nZVI-BC for the immobilization of cadmium (Cd) in sediment and concomitant ecological consequences remains unclear. Herein, this study systematically investigated the effectiveness, environmental impacts and mechanisms of S-nZVI-BC for remediating of Cd polluted sediment and evaluated the contribution of iron reducing bacteria (IRB) for Cd immobilization. The Cd immobilization by S-nZVI-BC was superior to nZVI, BC, nZVI-BC and S-nZVI, with a maximum residual percentage increasing by 56.93%, the leachability decreasing by 94.48% and the availability reducing by 88.25%. The sediment pH, Eh, dissolved organic carbon (DOC) and leaching Fe2+ played a vital role in Cd immobilization. Three enzyme activities (urease, sucrase, and cellulase) were enhanced after S-nZVI-BC treatment, suggesting an improvement in sediment quality. However, catalase activity decreased, possibly because of the influence of Fe2+ from S-nZVI-BC. The microbial community structure was changed and the abundance of some IRB was improved by S-nZVI-BC. The RT-qPCR results indicated that the absolute abundance of Clostridium (a typical IRB) increased by 1.66 log, which enhanced the iron cycle and Cd re-immobilization. The characterization results confirmed that Cd immobilization by S-nZVI-BC was achieved via adsorption, surface adsorption-complexation and precipitation. Therefore, S-nZVI-BC showed excellent Cd immobilization performance and long-term stability, being well adapted for the treatment of Cd polluted sediment. [Display omitted] • S-nZVI-BC maintained high efficiency for Cd immobilization even after 90 days. • The sediment properties played a vital role in Cd immobilization by S-nZVI-BC. • S-nZVI-BC enhanced the enzymatic activities (urease, sucrase and cellulase). • The iron reducing bacteria (Clostridium) promoted Cd immobilization by S-nZVI-BC. • Adsorption, complexation and precipitation dominated Cd immobilization. [ABSTRACT FROM AUTHOR]