Contamination of groundwater by energetic compounds such as TNT and RDX is of significant concern at Department of Defense (DoD) facilities. Application of currently available technologies to address this concern has, in some cases, involved high cost and limited efficacy.
The objective of this project was to evaluate sequential electrolytic transformation of the aqueous phase energetic compounds, TNT and RDX.
Recent collaboration between Colorado State University and the Environmental Security Technology Certification Program (ESTCP project ER-200112) has demonstrated the potential utility of electrolytic degradation of organic compounds in a permeable reactive barrier format (i.e., e-barrier). The concept of an e-barrier involves a panel of closely spaced permeable electrodes installed in a trench that intercepts a plume of contaminated groundwater. Application of an electrical potential to the electrodes imposes oxidizing conditions at the positive electrode and reducing conditions at the negative electrode. Contaminated groundwater flowing through the e-barrier is subject to sequential oxidation and reduction.
This project was conducted in two phases, each involving batch and flow-through reactor experiments. The first phase of the project was intended to provide basic information regarding electrolytic transformation of energetic compounds and to provide proof-of concept data regarding the application of e-barriers to dissolved energetic compounds. The second phase involved experiments designed to identify reaction products and to provide information regarding transformation pathways.
This project provides insight into the electrolytic transformation of aqueous-phase energetic compounds. Results provide the basis for application of a novel approach to the in situ treatment of groundwater. The e-barrier approach for energetic compounds has transitioned to ESTCP for full-scale demonstration and validation at the Pueblo Chemical Depot under ESTCP project ER-200519. If successful, this approach has the potential to replace a high cost pump-and-treat system.
Proof-of-concept experiments indicated that TNT and RDX can be treated to high levels (90-97%) using the e-barrier approach. In Phase 2, experiments indicated that cathodic reduction was the primary mechanism for the observed transformation of TNT and RDX. Products of TNT transformation included nitrite, azoxynitrotoluene, and compounds of MW 78, 96, 98. Products identified during electrolytic transformation of RDX indicated that MNX, DNX, and nitramide are likely intermediates. MNX and DNX were detected at very low concentration, suggesting that they are short-lived intermediates. For both contaminants, multiple sequences of oxidation-reduction may be required to achieve target concentrations at some sites. (Project Completed – 2004)