Removal of chlorinated solvents from carbonate-buffered water by zero-valent iron

The performance of a ground level reactive cell, filled with Fe⁰, designed for the treatment of water contaminated by chlorinated solvents, having a total input concentration of approximately 2 mg 1⁻¹ of the principal contaminants trichloroethene and perchloroethene, was tested at the Milovice site in the Czech Republic. A residence time of 1.62 days in the box was sufficient to reduce concentrations to a fraction less than 0.015 of the initial concentration. However, incomplete degradation of cis-1,2-DCE was observed. Reactions approximated first-order kinetics. The principal changes of concentrations of inorganic dissolved species in the reactive cell occurred for Ca²⁺, HCO ₃ ⁻ , NO ₃ ⁻ (decreased) and for Fe (initially increased, then decreased). Changes for Ca²⁺ and HCO ₃ ⁻ were caused by the precipitation of secondary carbonate mineral phases such as aragonite and siderite with the minor presence of green rust-CO₃. Concentration changes were gradual, along the complete length of the cell with a maximum at the inlet zone. The observations were attributed to minor increases of pH and slow kinetics of precipitation in the carbonate-buffered system. The average porosity loss was estimated to be approximately 2.7 % of the initial porosity per year, suggesting the long-term function of the permeable reactive barrier.