Characterization and Performance of Granular Iron as Reactive Media for TCE degradation by Permeable Reactive Barriers

Abstract

The application of Permeable Reactive Barriers (PRBs), an innovative clean-up technology for in-situ groundwater remediation, represents an effective alternative to traditional pump-and-treat systems and has raised strong interest during recent years. From recent statistics of the Italian Water Research Institute (IRSA), trichloroethylene (TCE) from industrial activities is the most widespread contaminant in groundwater. The goal of the research was to test the suitability and performance of a high purity granular iron reactive medium for TCE degradation by PRBs. The suitability was evaluated based on chemical and physical characteristics of the material and the performance of the granular iron, in terms of TCE removal efficiency, was evaluated by column tests.The experimental results showed that the characteristics of the granular iron are suitable for application as a reactive medium, since the hydraulic conductivity values were fully consistent with those reported in the literature, and the leaching tests indicated a reduced release of heavy metals. The overall removal efficiency of TCE was higher than 97% in all the tests performed at the flow rate of 0.25 cm3 min-1 (corresponding to a groundwater flow velocity of 0.37 m d-1) both for the 100% iron and the iron-sand columns. Moreover, TCE degradation around 60% was observed even in the first section of the columns fortypical groundwater flow velocity. The TCE reduction in the outlet stream was confirmed by the assessment of chlorine mass balance and by the absence of any reaction intermediate detected by GC-MS.Finally, the concentration profiles in the columns were not in agreement with those expected for a chemistry-controlled kinetic regime. This suggests that TCE degradation rate may have been limited by precipitation phenomena, hindering the contaminant transport to the iron surface.