Efficacy and microbial responses of biochar-nanoscale zero-valent during in-situ remediation of Cd-contaminated sediment

In situ immobilization of heavy metals in sediments has been considered as a low-cost and eco-friendly remediation method. In this study, biochar (BC) and BC-nanoscale zero-valent iron composite (nZVI/BC) treatments with different doses were conducted to immobilize Cd in sediments in situ. The performance of BC and nZVI/BC in changing Cd mobility and bacterial community in sediment was investigated, and their remediation efficiencies at various pH values were also explored. After 140 d of remediation, the results showed that the application of BC and nZVI/BC reduced the released Cd concentrations in the overlying water and porewater by 31-69% and 26-73%, respectively. Compared to the control, the labile Cd in treated sediments was transformed to a stable fraction, and the TCLP (toxicity characteristic leaching produce) extracted Cd decreased by 7-29%. The reduction in Cd mobility was closely related to the additional dose of BC or nZVI/BC, and the presence of nZVI greatly enhanced the ability of nZVI/BC to stabilize Cd. Notably, nZVI/BC presented a higher restriction for Cd release from sediment than BC at various pH values, and both BC and nZVI/BC showed the highest remediation effects under alkaline condition. Bacterial community analysis indicated that the richness and diversity of bacterial communities with the low-dose treatments were enhanced, while inhibition was observed at high dose treatments due to changes in the pH and toxicity of BC and nZVI/BC. This study supplies new insights into the potential effects of BC and nZVI/BC application on Cd in situ immobilization in contaminated sediments. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

In this study, biochar and BC-nanoscale zero-valent iron composite were used to immobilize Cd in sediments, showing significant reductions in Cd release in water and porewater. The treatments were most effective under alkaline conditions, with nanoscale zero-valent iron composite displaying a higher restriction on Cd release compared to biochar. Bacterial community richness was enhanced with low-dose treatments, while inhibition was observed at high doses.