Grantee Research Project Results
Final Report: The BOHP/UV Process for Destruction of PFAS in Leachate and Groundwater: Tandem mechanistic advancement and pilot demonstration
EPA Grant Number: R839630Title: The BOHP/UV Process for Destruction of PFAS in Leachate and Groundwater: Tandem mechanistic advancement and pilot demonstration
Investigators: Cates, Ezra L
Institution: Clemson University
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2019 through July 31, 2022 (Extended to July 31, 2023)
Project Amount: $458,469
RFA: Practical Methods to Analyze and Treat Emerging Contaminants (PFAS) in Solid Waste, Landfills, Wastewater/Leachates, Soils, and Groundwater to Protect Human Health and the Environment (2018) RFA Text | Recipients Lists
Research Category: Human Health , Water Quality , Drinking Water , Water , PFAS Treatment
Objective:
Original Objectives. This work investigated the application of a semiconductor photocatalytic and VUV photolytic treatment methods and reactor systems to the destruction of poly-/perfluoroalkyl substances (PFAS) present in landfill leachate. The original objectives of the 3-year project were stated as:
1. Assess degradation kinetics of leachate-relevant poly/perfluorocarboxylic acids (PFCAs) by Bi3O(OH)(PO4)2/ultraviolet process (BOHP/UV) using catalyst particles prepared in the PI’s lab
2. Test hypothesized process modification for photocatalytic mineralization of perfluorosulfonates (PFSAs)
3. Conduct trials of leachate treatment in an integrated BOHP/UV commercial photocatalytic reactor (Purifics Photo-cat), with potential pretreatment via TiO2/UV for removal of dissolved organic carbon (DOC)
Revised Objectives. Work within the first year resulted in no-go decisions involving two components of the original plan. The decisions and associated results are explained in further detail in Section 4. First, the use of BOHP as a photocatalyst for PFAS destruction in raw leachate matrices was deemed ineffective; as a result, project tasks evolved to include more robust pretreatment for removal of DOC and improvement of UV transmittance (UVT254) and to focus on optimization of PFAS destruction via noncatalytic vacuum UV (VUV) photolysis. Advancements in photocatalytic treatment employing hBN particles were also made, though were limited by expiration of the work period and budget. Additionally, as part of a separate PFAS-related project funded by the Department of Defense (SERDP ER-18-1599), the commercial annular photocatalytic reactor originally proposed for use herein was determined to be inefficient for PFAS applications, with respect to photon/energy use. Therefore, simpler and more efficient stirred-tank batch reactors were incorporated into the project tasks. Preliminary findings ultimately led to pursuance and completion of the following objectives:
1. Identify common leachate constituents that cause quenching effects or otherwise detract from photocatalytic degradation efficiency of BOHP.
2. Optimize ferric iron coagulation of leachate for maximal DOC removal and UVT254 improvement via coagulation-ceramic membrane ultrafiltration pretreatment.
3. Assess the efficiency of VUV photolysis in degrading PFAS and PFAS precursors in both raw and pretreated leachate matrices.
4. Assess the efficiency of PFAS degradation in pretreated leachate by a hBN+UV photocatalytic process.
In pursuing both the original and revised objectives additional incidental findings about process aspects with relevance to addressing PFAS contamination in leachate were also revealed and reported herein.
Summary/Accomplishments (Outputs/Outcomes):
Photocatalytic Degradation of PFAS. Photocatalytic water treatment typically uses suspended semiconductor nanoparticles in combination with UV irradiation to drive heterogeneous redox reactions. Photons having energies greater than the semiconductor’s band gap energy (Eg) are absorbed to excite a valence band electron into the conduction band, resulting in a pair of charge carriers in the form of conduction band electrons (e–cb) and valence band holes (h+vb); these may react with water or dissolved molecules at the particle surface to result in reduction and oxidation, respectively. Conventional photocatalysts, such as TiO2, are ineffective treatment options for waters contaminated by poly-/perfluoroalkyl substances (PFAS), as the valence band holes are depleted quickly by reaction with chemisorbed water.1-4 Semiconductors comprising trivalent post-transition metal cations, however, have shown much greater activity in degrading perfluorocarboxylic acids (PFCAs), including β-Ga2O3, In2O3, BiPO4, and Bi3O(OH)(PO4)2 (BOHP; developed by the PI’s group).5 And beyond PFCA degradation, only one photocatalyst has been reported that degrades perfluorosulfonates (PFSAs) with reasonal energy input and timescales – hexagonal boron nitride (hBN).6 This discovery was reported by the PI’s group near the end of this project’s performance period.
Of the many media for which concerning levels of PFAS have been reported, contamination of landfill leachate presents considerable challenges to the solid waste sector. Considering the future regulatory environment surrounding PFAS, the presence of these contaminants is likely to severely limit leachate treatment and disposal options. The abovementioned PFAS-active photocatalysts have all been previously studied in relatively pure matrices, with no reports on application to landfill leachate. Leachate typically contains exceedingly high levels of chemical oxygen demand (COD) ranging up to 104 mg/L.7 Accordingly, UV-based processes are often considered untenable such waters, as the COD contents impart negligible UV transmittance (UVT254). Nonetheless, both UVC photocatalytic processes and vacuum UV (VUV) photolytic techniques cannot rely on long UV penetration depths anyway, since in these cases UV penetration is hampered by the suspended catalyst particles and water molecules, respectively. In addition to applying pretreatment techniques for reducing dissolved organic carbon (DOC) levels and increasing UVT, process design must incorporate photoreactors with vigorous mixing that rapidly cycles fluid elements to within direct contact with the lamps.
Methods:
1. Experimental methods pertaining to typical photocatalytic reactor setup and equipment, instrumental analyses, as well as data in Section 4.1 can be found Qanbarzadeh et al. (2021).8 Methods pertaining to hBN+UVC/VUV were published in Qanbarzadeh et al. (2023).6
2. Pretreatment methods. Leachate pretreatment was performed by sequential coagulation and ultrafiltration. Reagent grade ferric chloride hexahydrate (FeCl3·6H2O) from Ward’s Scientific (470301-380) was crushed to a powder prior to chemical dosing.
1000 mL borosilicate glass beakers purchased from Laboratory Product Sales (BK0112) were used as mixing vessels with a Phipps & Bird PB-700 Jartester. After slow and rapid mix periods were complete, 500 mL of coagulated leachate was transferred directly to 800 mL volume Amicon Stirred Cell Reservoir (Millipore Sigma 6028, RC-800). For low dose coagulation, 0.4 g/L FeCl3·6H2O was dosed to leachate previously adjusted to pH 4.00 by HCl, and rapid mixing at 300 RPM for 60 seconds was followed by slow mixing at 50 RPM for 19 minutes. For high dose coagulation, 10.0 g/L FeCl3·6H2O was dosed to leachate without pH adjustment and rapid mix at 200 RPM for 5 minutes was followed by slow mixing at 60 RPM for 25 minutes.
Bench-scale ultrafiltration was performed using 800 mL volume Amicon Stirred Cell Reservoir (Millipore Sigma 6028, RC-800) connected by polyethylene tubing to N2 gas to provide 24 PSI trans-membrane pressure and to a 10 mL volume Amicon Stirred Ultrafiltration Cell (Model 8010, Millipore Sigma 5121) containing one 25 mm diameter, 0.02 μm aluminum oxide Whatman Anodisc membrane (Millipore Sigma WHA68096002). A new 0.02 μm aluminum oxide Whatman Anodisc membrane was used to process each 500 mL volume (i.e., no membranes disc was used for ultrafiltration more than once and each was discarded after use). The 10 mL Amicon Stirred Ultrafiltration Cell was placed on a magnetic stir plate to provide internal stirring to simulate crossflow conditions although the configuration provides dead-end flow to the membrane disc. 250 mL polypropylene bottles were used to collect 300 mL of permeate produced by ultrafiltration and the 300 mL permeate volumes were stored in the dark at 4°C until later processing for VUV photolysis.
A photoreactor was constructed using a 2.5" diameter, 10” height glass tube adhered to a 2.8" diameter ceramic air diffuser (diameter of diffuser area = 2”) using Lord 7150A/B urethane adhesive. Air connections were provided using polyethylene tubing. An air flow meter was used to control the flow rate of compressed air provided during air bubbling experiments, with an air flow rate of 2.0 sL/min used in pretreated leachate and an air flow rate of 1.0 sL/min used in raw leachate. A lower air flow rate was used during air bubbling of raw leachate due to significant formation of a foam layer, which dissipated over time during irradiation. Control tests of DDI in the constructed photoreactor under VUV irradiation confirmed no increase in dissolved organic carbon (DOC) over time under VUV irradiation, suggesting no degradation of polyethylene tube, plastic components of the ceramic air diffuser, or the urethane adhesive over time due to VUV irradiation.
VUV/UVC and UVC-only emitting lamps and quartz sleeves were purchased from Atlantic Ultraviolet. Ballasts were purchased from Aqua Ultraviolet (57 W, 120 V, 60 Hz, 0.85 amps). During photolysis experiments, one UV lamp housed within a quartz sleeve was submerged in the center of the constructed photoreactor. During dark control experiments, the same submerged quartz sleeve configuration was utilized, but without a UV lamp inserted. Stirring was provided by a magnetic stir bar and stir plate during all photolysis and dark control experiments.
3. Other Materials. Polypropylene syringes (3 mL, HENKE-JECT®) and polypropylene syringe filters (EZFlow®, 13 mm diameter, 0.22 μm pore size) were procured from VWR. Deionized distilled water (DDI) was supplied from an in-house system. Hydrochloric acid (6N) and methanol (LCMS grade, ≥99.9%) were received from VWR. Standards for ion chromatography were created using calcium chloride (ACS grade), magnesium sulfate (ACS grade), potassium phosphate (ACS grade) and sodium nitrate (ACS grade) from VWR and sodium fluoride (99%) from Beantown Chemical. Potassium hydrogen phthalate (≥99.5%) from Acros Organics was used for preparation of dissolved organic carbon standards. Analytical standards for ICP-OES were purchased from Inorganic Ventures and high purity nitric acid (Aristar® Plus) was purchased from VWR. LCMS standards containing a mixture of 24 PFAS were obtained from Wellington Laboratories (PFAC-24PAR). LC-MS grade acetonitrile was purchased from EMD Millipore. Ammonium acetate (≥99.99%) was purchased from Sigma Aldrich. Ammonium hydroxide (ACS grade, 28-30% in water) was purchased from Thermo Scientific.
4. Leachate sample collection and storage. Leachate was collected in SC in two 5-gallon HDPE totes from Twin Chimneys landfill in Greenville County in September 2021 and stored at in the dark at 4°C. All glassware and laboratory implements (e.g. graduated cylinder for liquid measurement, metal spatula for dry chemical mass measurement) were washed before and after each use with methanol, and Liquinox detergent (Fischer Scientific 16-000-126) and DDI and dried by passive evaporation.
All experimental samples were collected via pipette extraction into 50 mL polypropylene centrifuge tubes (Laboratory Product Sales, L226021), 15 mL polypropylene centrifuge tubes (Laboratory Product Sales, L226001), or 6.5 mL polypropylene scintillation vials (Laboratory Product Sales, L212070). All experimental samples were stored in the dark at 4°C until analysis by all methods excluding IC. Samples were frozen prior to IC analysis, after all other analyses were performed, to prevent evaporation.
5. Analytical sample preparation. All samples were left on benchtop for 24 hours ahead of any experimental procedures or analysis to bring to room temperature from 4°C or 0°C storage temperature. Sample dilutions in preparation for analytical methods were performed in 50 mL polypropylene centrifuge tubes (Laboratory Product Sales, L226021), 15 mL polypropylene centrifuge tubes (Laboratory Product Sales, L226001), or 6.5 mL polypropylene scintillation vials (Laboratory Product Sales, L212070).
Samples for analysis of COD and UVA254 were unfiltered and diluted in DDI to appropriate concentration ranges (COD samples diluted 1:5 in DDI to prevent interference from Cl-, UVA254 diluted 1:20 in DDI to provide measurement within range of 0.0045 - 1.0 cm-1 per EPA method 415.3 recommendation). Samples for analysis of pH, turbidity, and color were unfiltered and undiluted. For all other analyses (DOC, TN, IC, ICP-OES, LC-MS) samples were filtered with 0.2 um PES syringe filters or 0.2 um PP syringe filters prior to dilution and analysis. DOC samples were diluted 1:100 for raw leachate and 1:20 for pretreated leachate in DDI, TN samples were diluted 1:100 in DDI for raw leachate and pretreated leachate, all IC samples were diluted 1:100 in DDI, ICP-OES samples were diluted 1:1 in 4% HNO3 to provide 2% HNO3 concentration and LC-MS samples were diluted 1:1 in LCMS-grade methanol.
After analytical sample preparation, excess volumes were stored in the dark at 4°C in case of need for remeasurement, excepting LC-MS samples which were not remeasured due to potential for evaporation of methanol.
6. Instruments
• UVA254: Varian Cary 50 Bio UV-Visible Spectrophotometer
• pH: Thermo Scientific Orion Star A211 pH meter
• Turbidity: Hach 2100 N Turbidimeter
• COD: Hach DRB 200 and DR 3900 with Hach TNT 822 HR COD vials
• Color: Hach DR 900 Multiparameter colorimeter
• DOC and TN: Shimadzu TOC-L Total Organic Carbon Analyzer (CSH/CSN with TNM-L)
• IC: Dionex Aquion Ion Chromatography System and Dionex IonPacAS9-HC column
• ICP-OES: Thermo Scientific iCAP 7400 Duo
• LC-MS: Shimadzu LCMS 8040
Conclusions:
The results of this study provide significant new insight on both the capabilities of semiconductor photocatalysis and photolysis, with respect to challenging water matrices, as well as some broadly applicable technological advancements toward addressing PFAS contamination from landfill leachates.
First, VUV photolytic degradation of PFCAs proved to be fairly robust, though of low efficiency. Despite both water and solutes heavily attenuating VUV and resulting in minimal penetration into the photoreactor, rapid mixing allowed observable photolysis, indicative of a pseudo-heterogeneous reaction with photons near the lamp surface. With respect to BOHP photocatalysis, two aspects were found to be critical in maintaining efficient treatment in high-strength matrices such as leachate:
(1) Oxidation/UV quenching species. Not only the total concentration of DOC, but also the nature of the DOC must be within certain limits in order to avoid quenching of the photocatalytic and photolytic PFAS degradation. To that end, pretreatment via coagulation and UF proved indispensable in lowering the DOC of the leachate from 930 to 402; more unexpected, however, was a disproportionate improvement in the UV transmittance of the matrix, indicating that more reduced forms of carbon (humic/fulvic substances, aromatics, etc.) were removed preferentially, leaving behind organics with less propensity to rapidly quench photo-generated oxidants or attenuate UVC. Furthermore, at pH values below 4, carboxylic acids become protonated and neutral, thus interacting minimally with the positively-charged BOHP surface. As a result, elevated VFA concentrations were less of a concern than anticipated. Lastly, elevated Fe2+ in raw leachate or from added FeCl3 was not problematic, as most iron was precipitated and filtered out during pretreatment, with the residual Fe2+ likely being rapidly oxidized during irradiation.
(2) Interference with PFAS adsorption. Since BOHP degrades PFCAs through direct heterogeneous reaction with hvb+, adsorption of the target compound is a crucial prerequisite to electron transfer. Importantly, degradation of short-chain PFCAs, which have low surface affinity, is not achieved by BOHP, and relied on VUV photolysis herein. Because of the oxidation of precursors and degradation of long-chain PFCAs, however, no removal of short-chain compounds was observed in leachate experiments, and instead concentrations increased during BOHP+UVC/VUV treatment during the timescales studied. Some removal of longer-chain PFCAs (PFOA and PFDA) was accomplished in pretreated leachate but was attributed solely to VUV photolysis. The concentrations of Cl– and SO42– (and other likely other anions) in both raw and acidified pretreated leachate were inevitably too high for efficient photocatalysis by BOHP, resulting from (1) potential for Cl– to quench hvb+, (2) catalyst surface charge neutralization by SO42–, and (3) a dampening of electrostatic attraction between the catalyst and PFCAs by double layer compression in the general presence of high ionic strength.8 Since elevated anion concentrations and high alkalinity are universal attributes of landfill leachate, the BOHP+UVC/VUV process is likely unsuitable for this matrix.
While most efforts herein were dedicated to utilization of BOHP particles, experiments toward the end of the project period indicated that hBN is substantially more effective in degrading PFAS in pretreated leachate, in agreement with recent work using groundwater matrices.6 Because PFAS adsorb to hBN via hydrophobic interaction, rather than electrostatic, elevated anions concentrations do not disrupt photocatalytic efficiency, and can even aid the process through salting-out effects.8 And while BOHP is incapable of degrading PFSAs, our data suggest that hBN+UVC/VUV is surprisingly efficient at degrading PFOS (but not the non-adsorbing PFBS). Experiments performed as part of a separate project also showed the hBN photocatalysis is less chain-length dependent than BOHP, though the generation rate of short-chain PFCA intermediates still exceeded the degradation rate of native compounds in the hBN/pretreated leachate experiments herein. Further research on the application of the hBN+UVC/VUV toward address PFAS in landfill leachate is warranted, as is further advancement and improvement of the hBN process and materials themselves.
References:
1. Li, X.; Zhang, P.; Jin, L.; Shao, T.; Li, Z.; Cao, J., Efficient Photocatalytic Decomposition of Perfluorooctanoic Acid by Indium Oxide and Its Mechanism. Environmental Science & Technology 2012, 46, (10), 5528-5534.
2. Shao, T.; Zhang, P.; Jin, L.; Li, Z., Photocatalytic decomposition of perfluorooctanoic acid in pure water and sewage water by nanostructured gallium oxide. Applied Catalysis B:
Environmental 2013, 142–143, 654-661.
3. Merino, N.; Qu, Y.; Deeb, R. A.; Hawley, E. L.; Hoffmann, M. R.; Mahendra, S., Degradation and Removal Methods for Perfluoroalkyl and Polyfluoroalkyl Substances in Water.
Environmental Engineering Science 2016, 33, (9), 615-649.
4. Lin, H.; Niu, J.; Ding, S.; Zhang, L., Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2–Sb, Ti/SnO2–Sb/PbO2 and Ti/SnO2–Sb/MnO2 anodes. Water Research 2012, 46, (7), 2281-2289.
5. Sahu, S. P.; Qanbarzadeh, M.; Ateia, M.; Torkzadeh, H.; Maroli, A. S.; Cates, E. L.,
Rapid Degradation and Mineralization of Perfluorooctanoic Acid by a New Petitjeanite Bi3O(OH)(PO4)2 Microparticle Ultraviolet Photocatalyst. Environmental Science & Technology Letters 2018, 5, (8), 533-538.
6. Qanbarzadeh, M.; DiGiacomo, L.; Bouteh, E.; Alhamdan, E. Z.; Mason, M. M.; Wang, B.;
Wong, M. S.; Cates, E. L., An Ultraviolet/Boron Nitride Photocatalytic Process Efficiently Degrades Poly-/Perfluoroalkyl Substances in Complex Water Matrices. Environmental Science & Technology Letters 2023, 10, (8), 705-710.
7. Renou, S.; Givaudan, J. G.; Poulain, S.; Dirassouyan, F.; Moulin, P., Landfill leachate treatment: Review and opportunity. Journal of Hazardous Materials 2008, 150, (3), 468-493.
8. Qanbarzadeh, M.; Wang, D.; Ateia, M.; Sahu, S. P.; Cates, E. L., Impacts of Reactor
Configuration, Degradation Mechanisms, and Water Matrices on Perfluorocarboxylic Acid Treatment Efficiency by the UV/Bi3O(OH)(PO4)2 Photocatalytic Process. ACS ES&T Engineering 2021, 1, (2), 239-248.
9. Lang, J. R.; Allred, B. M.; Field, J. A.; Levis, J. W.; Barlaz, M. A., National Estimate of Per- and Polyfluoroalkyl Substance (PFAS) Release to U.S. Municipal Landfill Leachate. Environmental Science & Technology 2017, 51, (4), 2197-2205.
10. Jin, L.; Zhang, P.; Shao, T.; Zhao, S., Ferric ion mediated photodecomposition of aqueous perfluorooctane sulfonate (PFOS) under UV irradiation and its mechanism. Journal of Hazardous Materials 2014, 271, 9-15.
11. Aziz, H. A.; Alias, S.; Assari, F.; Adlan, M. N., The use of alum, ferric chloride and ferrous sulphate as coagulants in removing suspended solids, colour and COD from semiaerobic landfill leachate at controlled pH. Waste Management & Research 2007, 25, (6), 556565.
12. Han, M.; Jafarikojour, M.; Mohseni, M., The impact of chloride and chlorine radical on nitrite formation during vacuum UV photolysis of water. Science of The Total Environment 2021, 760, 143325.
13. Cao, Y.; Lee, C.; Davis, E. T. J.; Si, W.; Wang, F.; Trimpin, S.; Luo, L., 1000-Fold Preconcentration of Per- and Polyfluorinated Alkyl Substances within 10 Minutes via Electrochemical Aerosol Formation. Analytical Chemistry 2019, 91, (22), 14352-14358.
14. Ebersbach, I.; Ludwig, S. M.; Constapel, M.; Kling, H.-W., An alternative treatment method for fluorosurfactant-containing wastewater by aerosol-mediated separation. Water Research 2016, 101, 333-340.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 9 publications | 2 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Qanbarzadeh M, DiGiacomo L, Bouteh E, Alhamdan EZ, Mason MM, Wang B, Wong MS, Cates EL. An ultraviolet/boron nitride photocatalytic process efficiently degrades poly-/perfluoroalkyl substances in complex water matrices. Environmental Science & Technology Letters 2023;10(8):705-710. |
R839630 (Final) |
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Qanbarzadeh M, Wang D, Ateia M, Sahu SP, Cates EL. Impacts of reactor configuration, degradation mechanisms, and water matrices on perfluorocarboxylic acid treatment efficiency by the UV/Bi3O(OH)(PO4)2 photocatalytic process. ACS ES&T Engineering 2020;1(2):239-248. |
R839630 (2021) R839630 (Final) |
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Supplemental Keywords:
hazardous waste remediation; water purification technologies; photocatalytic reduction, groundwater remediation; photocatalyst water disinfectionRelevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.