A flow-through cell for the electrochemical oxidation of perfluoroalkyl substances in landfill leachates

doi:10.1016/j.jwpe.2021.102210

Journal of Water Process Engineering

Volume 43, October 2021, 102210

https://doi.org/10.1016/j.jwpe.2021.102210 Get rights and content

Highlights

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A novel boron-doped diamond (BDD) flow-through cell was used for electrochemical treatment of landfill leachates.
•
Individual PFAAs concentrations were in the range of 10² − 10⁴ ng/L in six landfill leachates treated.
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Non-detect levels for PFOS and removal > 97 % for PFOA were reached for all leachates treated.
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The flow-through cell allows for a lower energy consumption than the traditional parallel-plate cell.

Abstract

A novel boron-doped diamond (BDD) flow-through cell was used to evaluate the electrochemical oxidation of perfluoroalkyl acids (PFAAs) in landfill leachates. Six different leachates with a concentration of individual PFAAs in the range of 10² − 10⁴ ng/L were treated. The performance of the flow-through cell was assessed and compared with synthetic solutions for the oxidation of two representative PFAAs: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Subsequently, the effect of current density and the variability of leachates composition was investigated for the electrochemical oxidation of PFAAs in real landfill leachates. Non-detect levels and >90% degradation was reached for PFOS and PFOA after 2 h of treatment for all leachates tested. Decreasing trends for perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), and perfluorohexanesulphonic acid (PFHxS), and increasing trends for perfluoropentanoic (PFPeA), perfluorobutanoic (PFBA), and perfluorobutanesulphonic acid (PFBS) were observed. The total PFAAs removal ranged from −138.6 to 73.5%. Correlations between the composition of the leachates and PFAAs removal percentages were determined. Overall, the results show the potential of electrochemical oxidation to oxidize PFAAs present in high strength water such as landfill leachates.

Graphical abstract

Introduction

Per-and polyfluoroalkyl substances (PFASs) are a group of synthetic chemicals widely used in multiple consumer products (e.g., tapestry, outdoor clothing, cleaning agents, non-stick cookware) and industrial processes (e.g., metal plating, fire-fighting foams, coatings, electronics) due to their unique surface-active properties and high chemical and thermal stability [1,2]. An estimate of 3000 PFASs have been identified, from which perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are two of the most studied compounds [3].

PFASs have triggered attention due to their recalcitrant nature and bioaccumulative potential that leads to their accumulation in water, sediments, soils, wildlife, and the human body [3]. Their exposure and accumulation in the human body have been associated with multiple health effects (e.g., inmunotoxicity, neurotoxicity, testicular and kidney cancer) [4,5]. As a result, the United States Environmental Protection Agency (USEPA) established a health advisory level (HAL) of 0.07 μg/L for the combined concentration of PFOA and PFOS in drinking water [6,7].

Multiple PFASs end their life cycle in landfills as municipal solid waste, and their presence has been reported in landfill leachates in a wide range of concentrations [8,9]. In 2013, for example, a range of 0.15–9.2 μg/L of PFOA was detected in 13 landfill leachate sites in the U.S [8]. A more recent study (2019), performed in Michigan U.S., estimated a daily flow of leachates from 32 landfills of over 1 million gallons with concentrations in the range of 16–3200 ng/L for PFOA and 9–960 ng/L for PFOS [10]. The concentration of PFASs in leachates is affected by various factors, including the heterogeneity of the waste disposed, climate, waste age, and seasonal variability in infiltration [8,9]. According to Lang et al., the most common PFASs present in landfill leachates in the U.S. are 5:3 fluorotelomer carboxylic acid (5:3 FTCA), perfluorohexanoic acid (PFHxA), perfluorobutanoic acid (PFBA), PFOA, 6:2 fluorotelomer carboxylic acid (6:2 FTCA), and perfluoropentanoic acid (PFPeA) [8]. Overall, PFASs ranging from C4-C8 chain length dominate the distribution profiles [11].

Wastewater treatment plants (WWTPs) receive landfill leachates as influents to be treated conventionally. Masoner et al. estimated that although landfill leachates accounted for only 1.7% of the total daily flow that goes into the studied WWTPs, the contribution of total PFASs corresponded to 18% of the total PFASs present in the influent of WWTPs [12]. In addition, previous studies have shown higher concentrations of PFASs in the effluent compared to the influent [8,13]. This observation has been attributed to: 1) the non-biodegradability of PFAS; and 2) the fact that multiple polyfluoroalkyl substances (i.e., precursor compounds) can be further oxidized to perfluoroalkyl substances during biological treatment [8,14]. Some of the precursors include fluorotelomer based substances (FTCAs), perfluoroalkyl sulfonamide derivatives (FASAAs), and polyfluoroalkyl phospahate esters (PAPs) [15,16].

Additional treatment technologies, including adsorption with granular activated carbon (GAC) and membrane processes, i.e., nanofiltration (NF) and reverse osmosis (RO), have been proposed to treat PFASs in landfill leachates [3]. However, the complex composition of a landfill leachate makes GAC inefficient, while for the case of membrane processes, the concentrate containing PFASs require further treatment. Therefore, there is an urgent need for a destructive technology to degrade PFASs and break the accumulation cycle generated by other technologies.

Electrochemical oxidation has shown to be a versatile destructive technology due to its capability to degrade a wide range of contaminants, operation at ambient temperature and pressure, and robust performance [17,18]. Additionally, it does not require auxiliary chemicals and can be operated as a decentralized treatment option [18].

Multiple studies have been conducted to explore the electrochemical oxidation of PFASs in synthetic solutions and groundwater, showing promising results [19,20,21]. However, the effectiveness of the process in complex matrices, e.g., landfill leachate, membrane concentrates, and ion exchange regenerate solutions has been scarcely reported. Although the electrochemical oxidation of PFOA and PFOS in landfill leachates has recently been reported [17], multiple other PFAAs, commonly present in leachates, have only been identified but their oxidation has yet to be addressed.

This study explores, for the first time, the electrochemical oxidation of multiple PFAAs in real landfill leachates using a boron-doped diamond (BDD) flow-through cell. The objectives of this work were to: i) evaluate and compare the degradation kinetics and energy consumption for the electrochemical oxidation of two commonly studied PFASs (PFOA and PFOS) in a synthetic solution with a BDD flow-through cell; ii) assess the electrochemical oxidation of PFAAs in landfill leachates; and iii) determine the influence of leachate composition in the electrochemical oxidation of PFAAs in landfill leachates.

Section snippets

Materials

Perfluorooctanoic acid (PFOA, >97%), heptadecafluorooctanesulfonic acid potassium salt (CF₃(CF₂)7SO₃K, >98%), perfluorobutanoic acid (PFBA, >98%), sodium sulfate (Na₂SO₄) and sodium chloride (NaCl) were purchased from Sigma Aldrich.

Landfill leachates

Six leachate samples were collected from August 2019 to February 2020 from three different landfills in Michigan, USA. To maintain the confidentiality of sample locations, in this study, leachates were labeled as L1, L2, L3, L4, L5, and L6. The physico-chemical

Performance of the BDD flow-through cell

The electrochemical oxidation of two common PFAAs: PFOA and PFOS in a synthetic solution was evaluated with the flow-through cell. The solution consisted of 70 μg/L of PFOA and 70 μg/L of PFOS dissolved in a 10 mM sodium sulfate (Na₂SO4) electrolyte. A current density of 50 mA/cm² was applied during electrochemical treatment. Fig. 2a shows the decrease in concentration of both PFOA and PFOS over time. Both species followed a pseudo-first order degradation kinetics (r² = 0.9672 for PFOA and r²

Conclusions

The results presented herein introduced a higher performance cell (flow-through) for the electrochemical oxidation of PFAAs, allowing for lower energy consumption and enhanced mass transfer than a conventional parallel-plate cell.

With the A/V ratio used, current densities equal to or greater than 150 mA/cm² were necessary to guarantee total PFAAs degradation and avoid a faster generation rate from precursors transformation.

Non-detect levels and degradation > 97% for the electrochemical

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research project was funded by the City of Grand Rapids (Michigan, U.S.) and Michigan Department of Environment, Great Lakes, and Energy (EGLE). The authors thank Dr. Sibel Uludag-Demirer, Emma Davis, and Marius Ebert for their help with various parts of this research. The authors also thank to Dr. Qi Hua Fan, Dr. Greg Swain, and Dr. Volodomyr Tarabara for their helpful discussions.

References (43)

A. Urtiaga et al.
Kinetics of the electrochemical mineralization of perfluorooctanoic acid on ultrananocrystalline boron doped conductive diamond electrodes
Chemosphere
(2015)
E.F. Houtz et al.
Poly-and perfluoroalkyl substances in wastewater: Significance of unknown precursors, manufacturing shifts, and likely AFFF impacts
Water Research
(2016)
H. Yan et al.
Perfluoroalkyl acids in municipal landfill leachates from China: occurrence, fate during leachate treatment and potential impact on groundwater
Sci. Total Environ.
(2015)
R.C. Buck et al.
Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins
Integr. Environ. Assess. Manag.
(2011)
Z. Wei et al.
Treatment of per- and polyfluoroalkyl substances in landfill leachate: status, chemistry and prospects
Environ. Sci. Water Res. Technol.
(2019)
L. Ahrens et al.
Fate and effects of poly- and perfluoroalkyl substances in the aquatic environment: a review
Environ. Toxicol. Chem.
(2014)
J.L. Butenhoff et al.
Human Health Risk Assessment of Perfluoroalkyl Acids
(2015)
U.S. EPA
Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA). EPA Document Number: 822-R-16-005
(2016)
U.S. EPA
Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS). EPA Document Number: 822-R-16-004
(2016)
J.R. Lang et al.
National estimate of per- and polyfluoroalkyl substance (PFAS) release to U.S. municipal landfill leachate
Environ. Sci. Technol.
(2017)

H. Hamid et al.

Review of the fate and transformation of per- and polyfluoroalkyl substances (PFASs) in landfills

Environ. Pollut.

(2018)

Statewide Study on Lanfill Leachate PFOA and PFOS Impact on Water Resource Recovery Facility Influent, Technical Report

(2019)

I. Fuertes et al.

Perfluorinated alkyl substances (PFASs) in northern Spain municipal solid waste landfill leachates

Chemosphere

(2017)

J.R. Masoner et al.

Landfill leachate contributes per-/poly-fluoroalkyl substances (PFAS) and pharmaceuticals to municipal wastewater

Environ. Sci. Water Res. Technol.

(2020)

J. Busch et al.

Polyfluoroalkyl compounds in landfill leachates

Environ. Pollut.

(2010)

L. Ahrens et al.

Wastewater treatment plant and landfills as sources of polyfluoroalkyl compounds to the atmosphere

Environ. Sci. Technol.

(2011)

H. Hamid et al.

Review of the fate and transformation of per- and poly fl uoroalkyl substances (PFASs)

Z. Wang et al.

A never-ending story of per- and polyfluoroalkyl substances (PFASs)?

Environmental Science & Technology

(2017)

M. Pierpaoli et al.

Electrochemical oxidation of PFOA and PFOS in landfill leachates at low and highly boron-doped diamond electrodes

J. Hazard. Mater.

(2020)

J. Radjenovic et al.

Challenges and opportunities for electrochemical processes as next-generation technologies for the treatment of contaminated water

Environ. Sci. Technol.

(2015)

Q. Zhuo et al.

Degradation of perfluorinated compounds on a boron-doped diamond electrode

Electrochim. Acta

(2012)

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¹: Present address: Geosyntec Consultants, Milwaukee, WI 53202, USA.

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A flow-through cell for the electrochemical oxidation of perfluoroalkyl substances in landfill leachates

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Landfill leachates

Performance of the BDD flow-through cell

Conclusions

Declaration of competing interest

Acknowledgements

Chemosphere

Water Research

Perfluoroalkyl acids in municipal landfill leachates from China: occurrence, fate during leachate treatment and potential impact on groundwater

Sci. Total Environ.

Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins

Integr. Environ. Assess. Manag.

Treatment of per- and polyfluoroalkyl substances in landfill leachate: status, chemistry and prospects

Environ. Sci. Water Res. Technol.

Fate and effects of poly- and perfluoroalkyl substances in the aquatic environment: a review

Environ. Toxicol. Chem.

Human Health Risk Assessment of Perfluoroalkyl Acids

Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA). EPA Document Number: 822-R-16-005

Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS). EPA Document Number: 822-R-16-004

National estimate of per- and polyfluoroalkyl substance (PFAS) release to U.S. municipal landfill leachate

Environ. Sci. Technol.

Review of the fate and transformation of per- and polyfluoroalkyl substances (PFASs) in landfills

Environ. Pollut.

Statewide Study on Lanfill Leachate PFOA and PFOS Impact on Water Resource Recovery Facility Influent, Technical Report

Perfluorinated alkyl substances (PFASs) in northern Spain municipal solid waste landfill leachates

Chemosphere

Landfill leachate contributes per-/poly-fluoroalkyl substances (PFAS) and pharmaceuticals to municipal wastewater

Environ. Sci. Water Res. Technol.

Polyfluoroalkyl compounds in landfill leachates

Environ. Pollut.

Wastewater treatment plant and landfills as sources of polyfluoroalkyl compounds to the atmosphere

Environ. Sci. Technol.

Review of the fate and transformation of per- and poly fl uoroalkyl substances (PFASs)

A never-ending story of per- and polyfluoroalkyl substances (PFASs)?

Environmental Science & Technology

Electrochemical oxidation of PFOA and PFOS in landfill leachates at low and highly boron-doped diamond electrodes

J. Hazard. Mater.

Challenges and opportunities for electrochemical processes as next-generation technologies for the treatment of contaminated water

Environ. Sci. Technol.

Degradation of perfluorinated compounds on a boron-doped diamond electrode

Electrochim. Acta