Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface OxidesEPA Grant Number: R827117
Title: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface Oxides
Investigators: Tratnyek, Paul G. , Westall, John C.
Institution: Oregon Graduate Institute of Science & Technology , Oregon State University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1998 through September 30, 2001 (Extended to November 30, 2002)
Project Amount: $374,252
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Sustainability , Land and Waste Management , Engineering and Environmental Chemistry
Recent work on the remediation of chlorinated solvents with permeable reactive barriers (PRBs) containing zero-valent iron has shown that remediation performance is strongly affected by the layers of precipitates that form on the iron surface over time. The goal of this study is to explore the extent to which long-term performance of PRBs can be predicted and enhanced through a mechanistic understanding of the role of precipitates in the treatment zone. The major hypotheses to be tested are (i) ferrous iron in authigenic precipitates provides the population of Oactive sitesO that mediates reduction of chlorinated solvents by Fe0, (ii) the rate of chlorinated solvent degradation can be explained and predicted from the rate at which contaminants access these active sites, and (iii) remediation performance can be inhibited or enhanced by non-target substances depending on their interaction with surface sites.
The hypotheses will be investigated through two complementary types of experiments: (i) Controlled cells will be used to investigate the role of precipitates and adsorbates on remediation performance using a range of standard and advanced electrochemical techniques. (ii) Column experiments will be done to investigate the temporal changes in PRBs using embedded Fe0-wire electrodes that allow in situ characterization of treatment efficiency (and removal for further study in controlled electrochemical cells). Precipitates from both types of experiments will be characterized in detail. Both experimental systems will be used to investigate the effects of OtreatmentsO such as inorganic anions found in groundwater (naturally or as co-contaminants) and surfactants used in soil washing and DNAPL mobilization.
The study will provide a kinetic and mechanistic model of how oxides and other precipitates affect the long-term performance of PRBs containing zero-valent iron. It will also explain how variations in solution chemistry are linked to changes in the oxide surface coatings, which then enhance or inhibit remediation performance. This project will assist regulators and engineers by providing a realistic quantitative basis for predicting long-term performance of PRBs, explaining modes of failure, and identifying promising methods for enhancement.