Factors Influencing Removal of Trichloroethylene in a Zero-Valent Iron Fenton System

Abstract

Trichloroethylene (TCE), a volatile organic compound commonly used as a solvent, is frequently detected in contaminated groundwater. In the zero-valent iron (ZVI) Fenton process, TCE can be eventually dechlorinated into non-toxic products, which is mainly caused by hydroxyl radicals derived from H₂O₂. However, some key factors in the dechlorination of TCE in the zero-valent iron Fenton process have not been studied clearly. In the present study, the effects of the initial TCE concentration, initial H₂O₂ concentration, dosage of ZVI, initial pH, and temperature on TCE degradation in the ZVI Fenton process were studied. In addition, the structure and surface morphology of the ZVI used in this study were analyzed through scanning electron microscopy (SEM), N₂ adsorption-desorption, and X-ray diffractometry (XRD). The experimental results demonstrated that the dosage of ZVI and initial H₂O₂ concentration had obvious impacts on TCE degradation. At a ZVI dosage of 2 g/L and an initial H₂O₂ concentration of 0.53 mol/L, more than 97% of TCE could be degraded within 24 h at 25 °C. We found that the ZVI Fenton process could efficiently degrade TCE at a broad pH range and room temperature, making it applicable to groundwater remediation. TCE degradation was associated with Fe²⁺ concentration. Spectroscopic analyses indicated that the oxide film formed on the ZVI surface was associated with Fe²⁺ concentration in enhanced TCE dechlorination. The ZVI Fenton process could work at a wide range of TCE concentrations (0-200 mg/L).

Keywords: Fenton process; groundwater; trichloroethylene (TCE); zero-valent iron (ZVI).

Figure 1

SEM diagrams of zero-valent iron (A) before reaction and of zero-valent iron (B) after reaction (enlarged 50,000 times).

Figure 2

N₂ adsorption–desorption isotherm of zero-valent iron (A) and pore size distribution of zero-valent iron (B).

Figure 3

XRD diagram of ZVI before and after Reaction.

Figure 4

The effects of initial TCE on TCE degradation (A) and dechlorination (B). Concentration profile of aqueous Fe(II) released from ZVI surface (C). (ZVI = 2 g/L, pH = 3, H₂O₂ = 0.53 mol/L, T = 25 °C).

Figure 5

The effects of dosage of ZVI on TCE degradation (A) and dechlorination (B). Concentration profile of aqueous Fe(II) released from ZVI surface (C). (TCE = 20 mg/L, pH = 3, H₂O₂ = 0.53 mol/L, T = 25 °C).

Figure 6

The effects of hydrogen peroxide concentration on TCE degradation (A) and dechlorination (B). Concentration profile of aqueous Fe(II) released from ZVI surface (C). (TCE = 20 mg/L, ZVI = 2g/L, pH = 3, T = 25 °C).

Figure 7

Effects of temperature on TCE degradation (A) and dechlorination (B). Concentration profile of aqueous Fe(II) released from the ZVI surface (C). Variation in kinetic constants of different temperature contents (D) (TCE = 20 mg/L, ZVI = 2 g/L, pH = 3, H₂O₂ = 0.53 mol/L).

Figure 8

The effects of initial pH on TCE degradation (A) and dechlorination (B), Concentration profile of aqueous Fe(II) released from ZVI surface (C), Heterogeneity tests (D) (TCE = 20 mg/L, ZVI = 2 g/L, H₂O₂ = 0.53 mol/L, T = 25 °C).

Figure 9

Effect of different addition materials on TCE degradation ratio. (TCE = 20 mg/L, ZVI = 2 g/L, H₂O₂ = 0.53 mol/L, pH = 7, T = 25 °C).