Exploring efficient reductive dechlorination in nitrate-containing groundwater: Does sulfidated microscale zero-valent iron coupled with anaerobic bacteria increase sustainability?

Coupling microscale zero-valent iron (mZVI) and anaerobic bacteria (AB) for removal of chlorinated aliphatic hydrocarbon (CAHs) in groundwater is challenging due to decreased efficiency and undesirable products caused by the coexisting nitrate (NO3-). Therefore, in this study, mZVI is modified using three methods (sulfidation, carbon modification, and Fe2+ dosing) and combined with AB to construct coupled systems to investigate the removal performance of trichloroethylene (TCE) in the presence of NO3-. Among all the treatments, sulfidated mZVI coupled with AB (S-mZVIbm/AB) yields the highest TCE removal efficiency, removal rate, electron efficiency, and complete dechlorination ratio, as well as improved N2 selectivity. Sustainability evaluation, which considers both technical and environmental indicators, show that S-mZVIbm/AB is the best remediation strategy with the lowest combined utility function value. The reaction kinetics, material characterization as well as bacterial community analysis in S-mZVIbm/AB prove that the sulfidation of mZVI enhances chemical dechlorination, which consequently weakens the chemical reduction of NO3- by mZVI and facilitates biodenitrification. These findings highlight the potential of S-mZVIbm/AB as a sustainable solution for groundwater remediation at CAHs-contaminated sites where NO3- coexists and provide some suggestions for its practical application.