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 NO. Therefore, the effect of NO 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 β-elimination by fresh S-ZVI that contained 85.31% Fe and 14.69% FeS in the presence of NO, demonstrating that NO did not affect the degradation pathway of TCE. While high concentration of NO (> 10 mg/L) competed for electrons at the Fe/FeO interface with degradation products, leading to a continuous rising of acetylene. Moreover, the rapid reduction of NO to NH (89.79%) at the Fe interface contributed to the release of 5.08 mM Fe from S-ZVI, which promoted the formation of FeO with excellent electron conduction properties on the surface of S-ZVI. Accordingly, NO 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 NO and TCE simultaneously and the presence of NO could effectively enhance the degradation of TCE in groundwater.