Degradation and Transformation of Trichloroethylene in Miscible-Displacement Experiments through Zerovalent Metals

Fate and transport of chlorinated solvents flowing through reactive barriers containing zerovalent metals are influenced by advection, dispersion, adsorption, and transformation reactions. Batch experiments or resident concentration column experiments have been used extensively to study reactions of zerovalent metals and for the design of in situ flow-through reactive barriers. However, extending results from batch or resident concentration column experiments to zerovalent metal flow-through systems may be challenging because sorption and degradation are indistinguishable, and nonequilibrium adsorption−desorption may occur. This study presents the first reported miscible-displacement experiments to study the fate and transport of chlorinated solvents flowing through zerovalent metals. The miscible-displacement experiments resulted in simultaneous breakthrough curves of trichloroethylene (TCE) and its reduction daughter product, ethylene. Pulses of dissolved TCE were introduced, at three different flow rates, into columns filled with sand, iron filings, or copper-plated iron filings (Cu−Fe). Column effluent was directed through a high performance liquid chromatography diode-array detector that determined concentrations of TCE and its degradation daughter products. Trichloroethylene did not degrade in the presence of sand. Slightly less TCE was observed with the Cu−Fe breakthrough curve than for the iron breakthrough curve. The simultaneous TCE and ethylene breakthrough curves were described with an equilibrium sorption/degradation model and a two-site partial nonequilibrium sorption model with degradation and production. Results of the experiments indicate that sorption is an important process to be considered when TCE is flowing through zerovalent metal systems.