Combined removal of chlorinated ethenes and heavy metals by zerovalent iron in batch and continuous flow column systems

The combined removal of chlorinated ethenes and heavy metals from a simulated groundwater matrix by zerovalent iron (ZVI) was investigated. In batch, Ni (5-100 mg L-1) enhanced trichloroethene (TCE, 10 mg L-1) reduction by ZVI (100 g L-1) due to catalytic hydrodechlorination by bimetallic Fe-0/Ni-0. Cr(VI) or Zn (5-100 mg L-1) lowered TCE degradation rates by a factor of 2 to 13. Cr(VI) (100 mg L-1) in combination with Zn or Ni (50-100 mg L-1) inhibited TCE degradation. Addition of 20% H-2(g) in the headspace, or of Zn (50-100 mg L-1), enhanced TCE removal in the presence of Ni and Cr(VI). Sorption of Zn to ZVI alleviated the Cr(VI) induced inhibition of bimetallic Fe-0/ Ni-0 apparently due to release of protons necessary for TCE hydrodechlorination. In continuous ZVI columns treating tetrachloroethene (PCE, 1-2 mg L-1) and TCE (10 mg L-1), and a mixture of the metals Cr(VI), Zn(II), and Ni(II) (5 mg L-1), the PCE removal efficiency decreased from 100% to 90% in columns operated without heavy metals. The PCE degradation efficiency remained above 99% in columns receiving heavy metals as long as Ni was present. The findings of this study indicate the feasibility and limitations of the combined treatment of mixtures of organic and inorganic pollutants by ZVI.