Performance Enhancement of Biogenetic Dulfidated Zero-Valent Iron for Trichloroethylene Degradation: Role of Extracellular Polymeric Substances

Chemical sulfidation has been considered as an effective strategy to improve the reactivity of zero-valent iron (S-ZVI). However, sulfidation is a widespread biogeochemical process in nature, which inspired us to explore the biogenetic sulfidation of ZVI (BS-ZVI) with sulfate-reducing bacteria (SRB). BS-ZVI could degrade 96.3% of trichloroethylene (TCE) to acetylene, ethene, ethane, and dichloroethene, comparable to S-ZVI (97.0%) with the same S/Fe ratio (i.e., 0.1). However, S-ZVI (0.21 d-1) exhibited a faster degradation rate than BS-ZVI (0.17 d-1) based on pseudo -first-order kinetic fitting due to extracellular polymeric substances (EPSs) excreted from SRB. Organic components of EPSs, including polysaccharides, humic acid-like substances, and proteins in BS-ZVI, were detected with 3D-EEM spectroscopy and FT-IR analysis. The hemiacetal groups and redox-activated protein in EPS did not affect TCE degradation, while the acetylation degree of EPS increased with the concentration of ZVI and S/Fe, thus inhibiting the TCE degradation. A low concentration of HA -like substances attached to BS-ZVI materials promoted electron transport. However, EPS formed a protective layer on the surface of BS-ZVI materials, reducing its TCE reaction rate. Overall, this study showed a comparable performance enhancement of ZVI toward TCE degradation through biogenetic sulfidation and provided a new alternative method for the sulfidation of ZVI.

Automated summary

Chemical sulfidation is effective in improving the reactivity of zero-valent iron (S-ZVI). Inspired by the biogeochemical process of sulfidation in nature, researchers explored the biogenetic sulfidation of ZVI (BS-ZVI) using sulfate-reducing bacteria (SRB). BS-ZVI showed a degradation rate of 96.3% for trichloroethylene (TCE), comparable to S-ZVI (97.0%), but with a slower degradation rate due to extracellular polymeric substances (EPS) excreted by SRB. Organic components of EPS, including polysaccharides, humic acid-like substances, and proteins, were detected in BS-ZVI. The acetylation degree of EPS increased with ZVI and S/Fe concentration, inhibiting TCE degradation. Overall, this study demonstrated the potential of biogenetic sulfidation as an alternative method for improving the reactivity of ZVI.