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6CCVD Research

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

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-08-31
JournalWater
AuthorsAmy Yanagida, Elise Webb, Clifford E. Harris, Mark Christenson, S. D. Comfort
InstitutionsUniversity of Nebraska–Lincoln, AirLift Environmental (United States)
Citations22
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”
  • Core Value Proposition: Demonstrated the efficacy and scalability of electrochemical oxidation (EC) using Boron-Doped Diamond (BDD) electrodes as a cost-effective, chemical-free alternative to incineration for treating Per- and Polyfluoroalkyl Substances (PFAS) in contaminated water (simulated Investigation-Derived Waste, IDW).
  • Pilot-Scale Achievement: Successfully treated 189 L of simulated IDW (initial concentrations <10 ”g L-1 PFOA/PFOS) using a custom-designed, low-cost, 3D-printed, four-electrode flow-through reactor.
  • Performance Metrics: PFOS concentrations were reduced from 9.62 ”g L-1 to non-detectable (<0.05 ”g L-1) in less than 200 hours. PFOA was reduced from 8.16 ”g L-1 to 0.114 ”g L-1 over 450 hours.
  • Mechanism Confirmation: Using 14C-labeled PFOA, the study confirmed direct anodic oxidation of the carboxylic head (-14COOH → 14CO2) and achieved up to 60% defluorination (release of bonded fluorine).
  • Kinetic Control: Increasing current density shifts the reaction kinetics from current-controlled (zero-order) to mass-transfer controlled (first-order), indicating that the rate becomes limited by PFAS transfer to the BDD surface at higher power inputs.
  • Optimization for Longevity: Polarity switching (reversing every 30 seconds) and increasing the number of electrodes (4 vs. 2) significantly improved degradation kinetics and are expected to extend BDD electrode lifespan by mitigating mineral deposits.
  • Chain Length Effect: Longer chain perfluorinated carboxylates (C8) exhibited faster defluorination rates than shorter chain compounds (C3, C4, C6), confirming that the degradation products (shorter chains) are also mineralized by the EC-BDD process.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Anode MaterialBoron-Doped Diamond (BDD)N/ANeoCoatÂź mesh niobium substrate
BDD Coating Thickness5”mBoron concentration: 2500 ppm
BDD Oxygen OverpotentialUp to 2.5VRequired for direct anodic oxidation
Electrode Dimensions25 x 100 x 1.4mmDimensions of BDD mesh electrodes
Standard Current Density (Lab)8 to 40mA cm-2Corresponds to 0.2 A to 1.0 A
Standard Electrolyte10mMNa2SO4 background matrix
Standard pH (Acidified)2.5N/AAdjusted using H2SO4
Maximum Lab PFOA Rate (k)1.577h-14 BDD, 2 power sources, polarity switching
Pilot Volume Treated189LSimulated IDW in a 208 L barrel
Pilot Flow Rate2.33L min-181-minute cycle time for 189 L
Pilot Current1AUsed for 189 L treatment
Pilot PFOS Reduction9.62 to <0.05”g L-1Achieved in <200 hours
Pilot PFOA Reduction8.16 to 0.114”g L-1Final concentration after 450 hours
Pilot PFOS Rate Constant (k)0.0336h-1First-order rate constant
Pilot PFOA Rate Constant (k)0.0100h-1First-order rate constant
3D Reactor Housing CostLess than 100USDMaterial cost for custom printed parts

Key Methodologies

Section titled “Key Methodologies”
  1. Batch Reactor Setup: Experiments were conducted in a stirred 600 mL Erlenmeyer flask containing 500 mL of PFAS solution (8 ”g L-1 to 100 mg L-1), spiked with 14C-PFOA for kinetic tracking.
  2. Electrolyte and pH Control: Solutions were standardized with 10 mM Na2SO4 electrolyte. For most kinetic studies, the pH was adjusted to 2.5 using H2SO4 to ensure accurate measurement of 14CO2 evolution via LSC.
  3. Electrode Configuration: BDD electrodes (25 x 100 mm mesh) were used as anodes, paired either with a Pt/Ti wire cathode or a second BDD electrode acting as the cathode, maintaining a 5 mm electrode spacing.
  4. Current Density Variation: Electrical current was varied (0.2 A, 0.4 A, 1.0 A) to achieve current densities ranging from 8 to 40 mA cm-2, allowing quantification of the shift between current-controlled (zero-order) and mass-transport controlled (first-order) kinetics.
  5. Defluorination Measurement: Fluoride release was monitored temporally using a Dionex DX-120 ion chromatograph (IC) to quantify the extent of C-F bond cleavage and mineralization.
  6. Pilot Reactor Fabrication: A custom, four-electrode, flow-through reactor was designed using SOILDWORKS and 3D printed using MakerBot filament plastic, ensuring forced contact between the solution and the BDD electrodes (1 cm spacing).
  7. Pilot Operation Parameters: The 189 L simulated IDW was circulated continuously. The system utilized a custom DC power supply (500 W rheostat) set at 1 A, with polarity switching implemented every 30 seconds to enhance performance and reduce salt fouling on the electrodes.

Commercial Applications

Section titled “Commercial Applications”

The research supports the deployment of electrochemical oxidation technology for environmental remediation, particularly focusing on matrices contaminated with persistent organic pollutants.

  • PFAS Remediation in IDW: Direct application for treating Investigation-Derived Waste (IDW) water generated during site investigations at military bases, airports, and industrial facilities, offering a scalable, non-incineration disposal method.
  • Aqueous Film Forming Foam (AFFF) Site Cleanup: Treatment of groundwater and surface water contaminated by historical use of AFFF, targeting both PFOA and PFOS.
  • Concentrate Treatment: High-efficiency destruction of PFAS in concentrated waste streams, such as spent granular activated carbon (GAC) regenerant or brine from reverse osmosis (RO) systems, where high current densities are most effective.
  • Modular Water Treatment Systems: Development of low-cost, field-deployable, modular electrochemical reactors utilizing 3D printing techniques for housing and flow control, suitable for remote or temporary remediation sites.
  • Advanced Oxidation Processes (AOPs): Integration of BDD electrode technology into industrial wastewater treatment plants requiring the mineralization of highly recalcitrant organic compounds beyond standard biological or chemical methods.
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 ”g L−1). Temporal monitoring of PFAS with LC/MS/MS in this pilot study showed that PFOS concentrations decreased from 9.62 ”g L−1 to non-detectable (<0.05 ”g L−1) while PFOA dropped from a concentration of 8.16 to 0.114 ”g 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

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1999 - Determination of perfluorocarboxylates in groundwater impacted by fire-fighting activity [Crossref]
  2. 2003 - Occurrence and persistence of perfluorooctanesulfonate and other perfluorinated surfactants in groundwater at a fire-training area at Wurtsmith Air Force Base, Michigan, USA [Crossref]
  3. 2004 - Quantitative determination of fluorotelomer sulfonates in groundwater by LC MS/MS [Crossref]
  4. 2016 - Responding to emerging contaminant impacts: Situational management
  5. 1997 - Fluorinated organics in the biosphere [Crossref]
  6. 2008 - Understanding organofluorine chemistry. An introduction to the C-F bond [Crossref]
  7. 2008 - Are PFCAs Bioaccumulative? A critical review and comparison with regulatory criteria and persistent lipophilic compounds [Crossref]
  8. 2007 - Perfluoroalkyl acids: A review of monitoring and toxicological findings [Crossref]
  9. 2009 - Neonatal exposure to PFOS and PFOA in mice results in changes in proteins which are important for neuronal growth and synaptogenesis in the developing brain [Crossref]

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