Using Electrochemical Oxidation to Remove PFAS in Simulated Investigation-Derived Waste (IDW) - Laboratory and Pilot-Scale Experiments

At a Glance

Metadata	Details
Publication Date	2022-08-31
Journal	Water
Authors	Amy Yanagida, Elise Webb, Clifford E. Harris, Mark Christenson, S. D. Comfort
Institutions	University of Nebraska–Lincoln, AirLift Environmental (United States)
Citations	22
Analysis	Full AI Review Included

Technical Documentation & Analysis: Electrochemical PFAS Destruction using BDD Electrodes

Executive Summary

This research validates the efficacy of electrochemical oxidation using Boron-Doped Diamond (BDD) electrodes for the destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Investigation-Derived Waste (IDW). 6CCVD specializes in providing the high-performance BDD materials required for scaling this critical environmental remediation technology.

Core Achievement: Demonstrated near-complete transformation of PFOA and rapid destruction of PFOS in simulated IDW using EC-BDD technology.
Material Validation: Confirmed that BDD anodes, due to their high oxygen overpotential (up to 2.5 V), are ideal for generating the hydroxyl radicals necessary for direct anodic oxidation of recalcitrant organic contaminants like PFAS.
Kinetic Optimization: Degradation kinetics were successfully controlled by adjusting current density, shifting the reaction from current-controlled (zero-order) to mass-transfer controlled (first-order), achieving a maximum PFOA rate constant of $k = 0.946 \text{ h}^{-1}$.
Defluorination Success: Achieved up to 60% defluorination of PFOA, confirming the mineralization of the parent compound and subsequent shorter-chain degradation products (C3, C4, C6).
Scalability Demonstrated: A low-cost, custom 3D-printed reactor utilizing four BDD electrodes successfully treated 189 L of simulated IDW, validating the technology for pilot-scale deployment.
Electrode Lifespan Management: Polarity switching (every 30 seconds) was shown to improve degradation rates ($k = 1.256 \text{ h}^{-1}$) and mitigate anodic wear and salt buildup, enhancing BDD operational longevity.

Technical Specifications

The following hard data points were extracted from the laboratory and pilot-scale experiments detailing the EC-BDD system performance for PFAS degradation.

Parameter	Value	Unit	Context
Electrode Material	Boron-Doped Diamond (BDD)	N/A	Polycrystalline coating on Niobium mesh
BDD Coating Thickness	5	µm	Nominal thickness used by NeoCoat®
Boron Doping Level	2500	ppm B	Doping concentration for high overpotential
Electrode Dimensions	$25 \times 100 \times 1.4$	mm	Standard plate size used in reactors
Current Density Range	8 to 40	mA cm^-2	Corresponds to 0.2 A to 1.0 A (on 25 cm² area)
Optimal Operating pH	2.5	N/A	Acidified condition using $\text{H}{2}\text{SO}{4}$
Max PFOA Degradation Rate	0.946	h^-1	First-order kinetics at 40 mA cm^-2
Pilot PFOS Degradation Rate	0.0336	h^-1	208 L barrel experiment
Pilot PFOA Degradation Rate	0.0100	h^-1	208 L barrel experiment
Maximum Defluorination	60	%	Observed for PFOA after 3 hours
Pilot Volume Treated	189	L	Simulated IDW
Polarity Switching Frequency	Every 30	seconds	Used to improve kinetics and lifespan

Key Methodologies

The electrochemical oxidation process relied on precise control of material properties and operating parameters to achieve efficient PFAS destruction.

Electrode Fabrication: Polycrystalline BDD (PCD structure) was deposited as a 5 µm thick coating with 2500 ppm Boron doping onto a Niobium mesh substrate.
Reactor Configuration: Experiments utilized either 600 mL stirred batch reactors or a custom 3D-printed flow-through reactor designed to hold 2 or 4 BDD electrodes with a fixed 5 mm spacing.
Power Application: Direct Current (DC) power supplies (30 V/20 A) were used to maintain constant current densities ranging from 8 to 40 mA cm^-2.
Electrolyte Management: Sodium sulfate ($\text{Na}{2}\text{SO}{4}$) was the primary electrolyte, typically maintained at $10 \text{ mM}$ concentration to ensure adequate electro-conductivity and minimize voltage drop.
pH Control: Solutions were typically acidified to pH 2.5 using diluted sulfuric acid ($\text{H}{2}\text{SO}{4}$) to optimize degradation kinetics, although the effect was mixed depending on the electrode setup.
Kinetic Analysis: Degradation rates were quantified using ${}^{14}\text{C}$-labeled PFOA tracked via Liquid Scintillation Counting (LSC) and fit to first-order rate expressions ($C = C_{0}e^{-kt}$).
Defluorination Measurement: Temporal release of fluoride ions ($\text{F}^{-}$) was monitored using Ion Chromatography (IC) to confirm the breaking of the C-F bonds and mineralization.
Pilot Optimization: The pilot system incorporated polarity switching relays to reverse DC flow every 30 seconds, demonstrating a method to enhance performance and manage salt buildup on the electrode surface.

6CCVD Solutions & Capabilities

The successful implementation of EC-BDD technology for PFAS remediation hinges on the quality, customization, and reliability of the diamond electrodes. 6CCVD is uniquely positioned to supply the materials and engineering support necessary to replicate and scale this research.

Applicable Materials

The research utilized high-quality polycrystalline BDD electrodes on a Niobium mesh. 6CCVD provides equivalent or superior materials tailored for high-power electrochemical applications:

Heavy Boron-Doped Polycrystalline Diamond (BDD-PCD): We offer BDD films with doping concentrations optimized for high oxygen overpotential, ideal for generating the hydroxyl radicals required for PFAS destruction. Our standard BDD films are available on various conductive substrates, including Niobium (Nb), Titanium (Ti), or Silicon (Si).
Custom Doping and Thickness: While the paper used a 5 µm film, 6CCVD offers BDD films up to 500 µm thick, providing extended operational lifespan and robustness crucial for industrial IDW treatment systems.
SCD for Research Extension: For fundamental studies requiring ultra-high purity and precise surface control (e.g., investigating anodic wear or radical generation mechanisms), 6CCVD supplies Single Crystal Diamond (SCD) substrates, which can be custom doped with Boron.

Customization Potential

The research highlighted the need for custom electrode geometries (e.g., $25 \times 100 \text{ mm}$ plates) and specific reactor designs (3D printed flow-through cells). 6CCVD’s in-house capabilities directly address these requirements:

Custom Dimensions and Shapes: We provide BDD plates and wafers up to 125 mm in diameter (PCD). We offer precision laser cutting services to match the exact $25 \times 100 \text{ mm}$ dimensions used in the study, or to create complex geometries required for optimized flow-through reactors.
Integrated Metalization: The study utilized $\text{Pt}/\text{Ti}$ wire cathodes. 6CCVD offers internal metalization services (Au, Pt, Pd, Ti, W, Cu) for creating robust electrical contacts, counter electrodes, or multi-layer adhesion layers directly on the diamond or substrate material, ensuring reliable performance under high current loads.
Surface Finish: While the paper focused on chemical activity, surface quality impacts flow dynamics and fouling. We offer polishing down to $\text{Ra} < 5 \text{ nm}$ for inch-size PCD, ensuring consistent surface characteristics across large electrode areas.

Engineering Support

The paper noted challenges related to optimizing kinetics, managing current density transitions (zero-order to first-order), and mitigating salt buildup/anodic wear.

Application Expertise: 6CCVD’s in-house PhD engineering team specializes in diamond electrochemistry and can provide consultation on material selection, doping optimization, and system design for EC-BDD PFAS Remediation projects.
Process Optimization: We assist clients in defining the optimal BDD specifications (doping level, thickness, substrate choice) based on target current density and expected contaminant load, ensuring maximum efficiency and electrode lifespan.
Global Supply Chain: We ensure reliable, global shipping (DDU default, DDP available) of custom BDD electrodes, supporting pilot and full-scale remediation projects worldwide.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Repeated use of aqueous firefighting foams at military aircraft training centers has contaminated groundwater with per and polyfluorinated alkyl substances (PFAS). To delineate the extent of PFAS contamination, numerous site investigations have occurred, which have generated large quantities of investigation-derived wastes (IDW). The commonly used treatment of incinerating PFAS-tainted IDW is costly, and was recently suspended by the Department of Defense. Given long-term IDW storage in warehouses is not sustainable, our objective was to use electrochemical oxidation to degrade PFAS in contaminated water and then scale the technology toward IDW treatment. This was accomplished by conducting a series of laboratory and pilot-scale experiments that electrochemically oxidized PFAS using direct current with boron-doped diamond (BDD) electrodes. To improve destruction efficiency, and understand factors influencing degradation rates, we quantified the treatment effects of current density, pH, electrolyte and PFAS chain length. By using 14C-labeled perfluorooctanoic acid (PFOA) and tracking temporal changes in both 14C-activity and fluoride concentrations, we showed that oxidation of the carboxylic head (-14COOH → 14CO2) was possible and up to 60% of the bonded fluorine was released into solution. We also reported the efficacy of a low-cost, 3D printed, four-electrode BDD reactor that was used to treat 189 L of PFOA and PFOS-contaminated water (Co ≤ 10 µg L−1). Temporal monitoring of PFAS with LC/MS/MS in this pilot study showed that PFOS concentrations decreased from 9.62 µg L−1 to non-detectable (<0.05 µg L−1) while PFOA dropped from a concentration of 8.16 to 0.114 µg L−1. Efforts to improve reaction kinetics are ongoing, but current laboratory and pilot-scale results support electrochemical oxidation with BDD electrodes as a potential treatment for PFAS-tainted IDW.

Tech Support

Original Source

DOI: https://doi.org/10.3390/w14172708

References

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