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6CCVD Research

Efficient removal of 2,4,6-trinitrotoluene (TNT) from industrial/military wastewater using anodic oxidation on boron-doped diamond electrodes

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-02-27
JournalScientific Reports
AuthorsMaƂgorzata SzopiƄska, Piotr PrasuƂa, Piotr Baran, Iwona Kaczmarzyk, Mattia Pierpaoli
InstitutionsMilitary Institute of Armament Technology, Military University of Technology in Warsaw
Citations5
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research demonstrates the highly efficient removal of the explosive compound 2,4,6-trinitrotoluene (TNT) from complex aquatic environments using Anodic Oxidation (AO) on Boron-Doped Diamond (BDD) electrodes.

  • High Removal Efficiency: The AO process achieved >92% TNT removal within two hours and >99.9% removal within six hours when treating real-life environmental matrices (Treated Wastewater and Marine Water).
  • BDD Anode Superiority: BDD electrodes facilitate the direct production of the highly potent hydroxyl radical (·OH) via water oxidation, enabling the mineralization of persistent organic pollutants (POPs) like TNT without external chemical dosing.
  • Matrix Enhancement: The presence of chloride ions (saline environment) significantly enhanced the degradation rate, attributed to the formation of active chlorine species (Cl2,aq, HClO, ClO-).
  • Kinetic Performance: TNT degradation followed first-order kinetics (Ct/C0 = e(-At)), with the highest reaction rate constant (A = 1.70 h-1) observed in the high-conductivity marine water matrix.
  • Scalability and Robustness: The method is robust, operates under galvanostatic conditions (50 mA cm-2), and is proposed for full-scale, modular application in industrial and military sectors, supporting water circular economy initiatives.
  • By-product Management: While the process effectively reduces TNT concentration below 0.1 mg L-1, it generates intermediate oxidation products (e.g., TNB, DNB) and reduction products (amino-DNTs) at the stainless-steel cathode, necessitating further optimization (e.g., membrane separation or cathode material selection).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Anode MaterialBoron-Doped Diamond (BDD)N/AFabricated via MPCVD on Nb substrate.
Boron Doping Level ([B]/[C])2000ppmIn the gas phase during BDD deposition.
Substrate Temperature (Deposition)700°CBDD fabrication condition.
Microwave Power (Deposition)1300WBDD fabrication condition.
Anode Geometric Area (A)10.5cm2Undivided electrolytic cell setup.
Current Density (j)50mA cm-2Galvanostatic AO operating condition.
Initial TNT Concentration (C0)50mg L-1Spiked concentration in all matrices.
TNT Removal Efficiency (6 h)>99.9%Achieved in Treated Wastewater (TWW) and Marine Water (MW).
TNT Concentration (8 h, PBS)86”g L-1Measured via GC-MS/MS.
Highest Reaction Rate Constant (A)1.70h-1Observed in Marine Water (MW) matrix (1st order kinetics).
Energy Consumption (ECon)68.0 to 84.8kWh m-3High conductivity matrices (excluding TWW).
Conductivity (TWW)<2mS cm-1Low conductivity matrix.
Conductivity (MW)>10mS cm-1High conductivity matrix.
LOD (HPLC-PDA)2.9”g L-1Limit of Detection for TNT analysis.

Key Methodologies

Section titled “Key Methodologies”

The AO experiments utilized BDD electrodes fabricated via Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD) and tested in a 500-mL undivided electrolytic cell under galvanostatic control.

  1. BDD Electrode Fabrication:

    • Substrate Preparation: Nb substrates were sandblasted for surface roughening, cleaned (acetone/isopropanol), and seeded with a water-based nanodiamond slurry.
    • Growth Parameters: Substrate temperature was 700 °C, microwave power was 1300 W, and the process duration was 12 h.
    • Doping: Boron doping level was 2000 ppm ([B]/[C] ratio) in the gas phase.

  2. Anodic Oxidation (AO) Setup:

    • Reactor: Undivided electrolytic cell (500 mL volume) with a BDD anode (10.5 cm2) and a stainless-steel mesh cathode (2.5 cm separation).
    • Conditions: Galvanostatic operation maintained at a constant current density of 50 mA cm-2. Temperature was controlled at 20 ± 3 °C.

  3. Sample Preparation:

    • All matrices were spiked to an initial TNT concentration (C0) of 50 mg L-1.
    • Matrices: 0.1 M Phosphate Buffer Solution (PBS), Treated Wastewater (TWW), Baltic Sea Marine Water (MW), and PBS artificially spiked with 100 mg L-1 or 200 mg L-1 Cl-.

  4. Analytical Control:

    • TNT/Kinetics: High-Performance Liquid Chromatography with Photodiode Array (HPLC-PDA) was used for primary TNT concentration monitoring and kinetic analysis.
    • By-products: Gas Chromatography-Tandem Mass Spectrometry (GC-MS/MS) was employed to identify oxidation intermediates (e.g., TNB, DNB) and reduction products (e.g., amino-DNTs).
    • Electrochemical Sensing: Differential Pulse Voltammetry (DPV) using sp2-rich BDD/graphene nanowall electrodes provided real-time monitoring of TNT and its by-products.

Commercial Applications

Section titled “Commercial Applications”

The BDD-based AO technology is highly relevant for environmental remediation and industrial water management, particularly in sectors dealing with nitro-aromatic compounds.

  • Military and Defense Industry:
    • Treatment of “pinkwater” or “redwater” effluents generated during the manufacturing, processing, and demilitarization of TNT and other explosives.
    • Remediation of contaminated groundwater and soil leachates at military bases and production facilities.
  • Water Circular Economy (WCE):
    • Implementation as a modular, integrated treatment step for industrial wastewater streams, enabling water reuse and decoupling industrial growth from resource consumption, aligning with EU Green Deal objectives.
  • Saline Water Remediation:
    • Purification of highly conductive saline water (e.g., backwash streams, marine water) contaminated with explosives, leveraging the enhanced degradation kinetics observed in chloride-rich environments.
  • Advanced Oxidation Processes (AOPs):
    • Use as a robust tertiary treatment method for mineralizing persistent organic micropollutants (POPs) in complex matrices where traditional methods (biological, filtration) are ineffective or generate secondary waste.
  • Electrode Technology:
    • The BDD electrode material, known for its extreme chemical stability and high overpotential for oxygen evolution, is ideal for harsh electrochemical environments required for full mineralization.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1990 - Toxicity and Metabolism of Explosives [Crossref]

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