The role of nitrate in simultaneous removal of nitrate and trichloroethylene by sulfidated zero-valent Iron

Sulfidated zero-valent iron (S-ZVI) is commonly used to degrade trichloroethylene (TCE). The reactivity of S-ZVI is related to not only the properties of S-ZVI but also the geochemical conditions in groundwater, such as coexisted NO3-. Therefore, the effect of NO3- on TCE degradation by S-ZVI and its mechanism were systematically studied. 95.17% of TCE was degraded to acetylene, dichloroethene, ethene, ethane and multi-carbon products via beta-elimination by fresh S-ZVI that contained 85.31% Fe0 and 14.69% FeS in the presence of NO3-, demonstrating that NO3- did not affect the degradation pathway of TCE. While high concentration of NO3-(> 10 mg/L) competed for electrons at the Fe/FeO(x )interface with degradation products, leading to a continuous rising of acetylene. Moreover, the rapid reduction of NO3- to NH4+ (89.79%) at the Fe0 interface contributed to the release of 5.08 mM Fe2+ from S-ZVI, which promoted the formation of Fe3O4 with excellent electron conduction properties on the surface of S-ZVI. Accordingly, NO3- improved the degradation and electron selectivity of TCE by 51.07% and 2.79 fold, respectively. This study demonstrated that S-ZVI could remediate the contamination of NO3- and TCE simultaneously and the presence of NO3- could effectively enhance the degradation of TCE in groundwater.

Automated summary

This study systematically investigated the effect of NO3- on the degradation of TCE by S-ZVI and its mechanism. The results showed that NO3- did not affect the degradation pathway of TCE, but at high concentrations, it competed for electrons and led to an increase in the production of acetylene. Additionally, the presence of NO3- promoted the formation of Fe3O4, which improved the degradation efficiency of TCE.