The manufacture of munitions and load/assemble/pack (LAP) operations produce wastewaters that contain ppm-levels of various organic munitions constituents and inorganic oxyanions (i.e., nitrate (NO₃^-), perchlorate (ClO₄^-)). Munitions manufacturing facilities commonly use anaerobic/aerobic biological treatment, and LAP facilities use adsorbent-based treatment strategies. Due to stricter discharge limits and the manufacture of more water-soluble compounds, these current treatment practices are not sufficient. In addition, adsorbent-based treatment creates a concentrated waste that requires further treatment or disposal.

The overall objective of this project is to utilize a cost-effective reactive electrochemical membrane (REM) for the simultaneous degradation of various munitions constituents and IHEs from manufacturing wastewaters. Specific technical objectives include: 1) development of efficient, robust, and low-cost electrocatalysts for contaminant removal; 2) optimization of operating conditions for cost effective treatment; and 3) calculation of capital, operating, and maintenance costs for remediation using the REM and compare it to those determined for biological and adsorbent-based treatment strategies using cost and life cycle assessments.

This project will investigate the technical and economical feasibility of using REMs for treating wastewaters containing munitions constituents. The REM is a novel electroactive membrane made of porous Ti₄O₇ with micron-sized pores. Anodic polarization of the REM results in degradation of organic munitions constituents through a combination of direct electron transfer reactions and reactions with OH^• that are generated from water electrolysis, and perchlorate and nitrate are reduced on the REM cathode. The small pore size and operation in flow-through mode allows for very fast mass transfer, and thus complete elimination of compounds in a single pass through the REM.

The plan consists of REM and catalyst synthesis, a series of bench-scale experimental studies that will determine optimal operating conditions for removal of munitions constituents from wastewater samples, and a preliminary cost assessment. Experimental parameters that will be explored include: 1) adsorption capacity; 2) necessary residence time in the reactor; 3) needed membrane surface area per groundwater volume treated; and 4) energy usage (kWh/m³ water treated). The work is projected to end with proof of concept data that will determine if the REM is suitable for treatment of wastewater generated from the manufacture of munitions and at LAP operations.

The successful completion of this project will have numerous benefits to the Department of Defense (DoD) and the scientific community; these include 1) a better understanding of the use of electrochemical technologies for wastewater treatment of DoD priority contaminants; 2) the generation of proof of concept data that can be used to develop a prototype REM system for the remediation of wastewaters containing diverse munitions constituents; and 3) an energy cost assessment for using the REM technology at manufacturing sites, which can be used by practitioners to assess the REM technology as a viable treatment option. (Anticipated Project Completion - 2024)

Almassi, S., C. Ren, J. Liu, and B. Chaplin. 2022. Electrocatalytic Perchlorate Reduction Using an Oxorhenium Complex Supported on a Ti₄O₇ Reactive Electrochemical Membrane. Environmental Science and Technology, 56(5):3267–3276. doi.org/10.1021/acs.est.1c08220.

Ren, C. and J. Liu. 2021. Bioinspired Catalytic Reduction of Aqueous Perchlorate by One Single-Metal Site with High Stability Against Oxidative Deactivation. American Chemical Society Catalysis, 11(11):6715–6725. doi.org/10.1021/acscatal.0c05276.