High Rate Degradation of 3-Nitro-1,2,4-triazol-5-one (NTO) to Environmentally Benign End Products in Sequential Reducing-Oxidizing Reactive Mineral Packed Bed Reactors

Dr. Jim A. Field | University of Arizona

ER19-1075

Objective

The Department of Defense (DoD) is establishing the environmental and public health impacts of newly deployed insensitive high explosive (IHE) compounds. In particular, the IHE constituent, 3-nitro-1,2,4-triazol-5-one (NTO), is a concern due to its very high aqueous solubility (16,640 mg L-1) and low hydrophobicity. These properties are expected to provide conditions for elevated concentrations of NTO in munitions manufacturing wastewater. Likewise, NTO is very mobile in soil and aquifers creating the potential threat of surface water and groundwater contamination. Thus, there is a need to develop a cost-effective method that can target NTO as the predominant explosive in munitions wastewater or contaminated groundwater. The objectives of this project are to demonstrate that reactive minerals in a sequence of reducing and oxidizing packed bed reactors can rapidly degrade NTO to safe end-products. Additionally, the project will demonstrate whether the packed bed reactors can operate robustly over extended time periods, confirming their feasibility as a technological option.

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Technical Approach

The basis of this project's method is to utilize redox-active minerals with reactive surfaces to sequentially (i) reduce and (ii) oxidize the NTO molecule. In the first step, NTO will be reduced by zero-valent iron (ZVI) or green rust (a mixed-valent II/III iron mineral) to its daughter product, 3-amino-1,2,4-triazol-5-one (ATO), which is susceptible to surface-catalyzed oxidation. In the next step, ATO will be oxidized by birnessite (MnO2) to environmentally safe endproducts (urea, N2(g) and CO2(g)). In order for this technology to be a significant game changer, the project aims to accomplish each step with a hydraulic retention time of 5 min or less.

The overarching aim of the project is to demonstrate the feasibility of the sequential reactive mineral packed bed reactors system. The tasks are arranged around: 1) optimizing each of the sequential reactions; 2) assessing the longevity of the reactive minerals and developing methods to prevent surface passivation; 3) evaluating and controlling the solid phase mineralogy over time in the packed bed reactors; and 4) demonstrate the effectiveness of the process to treat simulated- and real wastewater. in bench-scale packed bed reactors.

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Benefits

The project will develop a high-rate packed bed reactor for the abiotic conversion of NTO to environmentally benign end-products (urea, CO2 and N2). This technology will rely on minerals like zerovalent iron that already are used in cost effective treatment systems targeting chlorinated solvents (e.g. perchloroethene). Both the rate at which ZVI reduces NTO and the rate at which birnessite oxidizes ATO are very high, allowing the application of cost-effective reactor systems with a small foot print and very short hydraulic retention times (in the order of minutes). The technology is particularly well suited for NTO and matches SERDP's previous identification of this new IHE compound as a potential problem in munitions wastewater due to its high aqueous solubility. This technology could be deployed for treatment of wastewater at munitions constituents manufacturing plants and load/assemble/pack operations. This technology could also be utilized in permeable reactive barriers (PRB) to treat NTO in groundwater or captured storm runoff water at DoD training/test ranges and, thus the project is also applicable to prevent the spread of NTO to surface water and groundwater. The sequential reactive mineral packed bed technology is also potentially applicable to other contaminants. Nitrate, RDX, 2,4-dinitroanisole (DNAN) are all known to be reduced by ZVI, and the reduced products of DNAN (2-amino-4-nitroanisole, and 2,4-diaminoanisole) are known to be oxidized by birnessite. 

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Points of Contact

Principal Investigator

Dr. Jim Field

University of Arizona

Phone: 520-621-0704

Program Manager

Environmental Restoration

SERDP and ESTCP

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