Grantee Research Project Results

Final Report: Electron Beam Technology for Destruction of Short-Chain and Perfluoroalkyl Substances in Groundwater, Wastewater, Sewage Sludges, and Soils

EPA Grant Number: R839650
Title: Electron Beam Technology for Destruction of Short-Chain and Perfluoroalkyl Substances in Groundwater, Wastewater, Sewage Sludges, and Soils
Investigators: Pillai, Suresh D , Staack, David , Sharma, Virender , Houtz, Erica , Juriasingani, Purshotam
Institution: Texas A&M Agricultural Research and Extension Center , Arcadis U.S. Inc. , Tetra Tech Inc.
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2019 through August 31, 2022 (Extended to February 29, 2024)
Project Amount: $899,164
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: PFAS Treatment , Drinking Water , Water Quality , Water , Human Health

Objective:

The specific objectives are:

1. To characterize and quantify the effectiveness of eBeam technology at degrading short-chain and perfluoroalkyl substances in PFAS-contaminated groundwater, wastewater, sewage sludges and soils

2. To develop a mechanistic understanding of eBeam-mediated breakdown of short chain PFAS eg., perfluoroheptanoate (PFHpA) in a groundwater and drinking water matrix

3. To perform an economic and technology feasibility analyses for a transportable eBeam treatment technology platform for ex-situ PFAS remediation

Summary/Accomplishments (Outputs/Outcomes):

The main goal of this EPA Science to Achieve Results (STAR) research project was to gain a comprehensive understanding of the effectiveness and economic viability of using eBeam as an ex-situ treatment technology for breaking down and eliminating PFAS compounds in groundwater, wastewater, biosolids, sludges, and soils. Additionally, the project aimed to advance our knowledge of utilizing eBeam technology for environmental PFAS remediation. The study employed a 10 MeV, 15 kW eBeam linear accelerator, and the alanine dosimetry system was utilized to measure the delivered eBeam doses.

We collected biosolid samples, composted biosolid samples, soil samples, groundwater samples, and landfill leachate samples from various locations across the United States. A significant feature of these studies is the use of authentic environmental samples to showcase the technology. Another noteworthy aspect is the substantial increase in the volume of environmental media compared to our earlier research. In these studies, we scaled up from using 50g of material to approximately 200g of solid media, representing a considerable expansion in scale.

In prior investigations, we established the necessity of high eBeam doses for meaningful PFAS degradation in environmental media. In treatments involving high eBeam doses (2000 kGy), sample temperatures could surpass 400°C, leading to rapid water evaporation and condensation. The design of the treatment vessel emerged as a crucial element in high eBeam dose experiments. Upon exposure to 2000 kGy, the PFOS concentrations in composted biosolid samples decreased from 59.3 ng/g in untreated samples to 2.01 ng/g in eBeam treated samples, showcasing a 94% total PFOS degradation. In non-composted biosolid samples, PFOS concentration decreased from 20.5 ng/g to 0.98 ng/g (93.6% reduction), and PFOA concentration in residual solids fell below analytical detection limits.

While the initial composted biosolid samples revealed detectable levels of 24 PFAS, 10 of them experienced complete degradation, and 11 exhibited degradation ranging between 77-98%. The treated material showed an accumulation of two precursor molecules, EtFOSE and MeFOSE. In contrast, non-composted sludge samples inherently featured a lower number of PFAS, with only 13 different PFAS present. Among these, 10 PFAS underwent complete breakdown, and 2 PFAS displayed breakdown percentages between 95-98% in eBeam treated samples. There was an observed accumulation of one precursor, namely EtFOSAA, after the treatment. We hypothesize that these accumulation products are probably degradation products of unknown (untargeted) precursors that accumulated in the sample during eBeam treatment.

We were interested in understanding the significance of elevated sample temperatures during high dose eBeam degradation. Therefore, we devised experiments to investigate the impact of temperature increase during a 2000 kGy treatment on PFAS degradation. To elucidate the temperature effects, we focused on incremental low eBeam doses (25 kGy) applied to PFAS-impacted biosolid samples and non-composted biosolid samples until reaching a total of 2000 kGy. This experimental approach allowed for the analysis of samples at 500 kGy, 1000 kGy, and 2000 kGy without the concurrent temperature increase.

A distinct difference emerged in the results obtained when the biosolid samples were directly exposed to 2000 kGy compared to sludge samples exposed to 2000 kGy incrementally (without concurrent temperature effects). In the composted biosolid samples, the reduction of PFOS was 14% at 500 kGy, 25% at 1000 kGy, and 47% at 2000 kGy, in contrast to the 97% reduction observed when the same biosolid samples were directly exposed to 2000 kGy. Therefore, approximately 50% of the observed PFOS reduction at high eBeam doses can be attributed to temperature effects, while the remaining 50% can be attributed to the involvement of radiation/ionization chemistry. This discovery represents an original finding derived from the outcomes of this project. The increase in PFOA concentration with an escalating dose further supports our earlier reports indicating that PFOA is a breakdown product of PFOS. Overall, when the samples underwent a 2000 kGy treatment without temperature involvement, the targeted PFAS exhibited degradation ranging from 27% to 100%. It is crucial to note that not all PFAS degradation is influenced by temperature, as some PFAS degraded by 100% even with incremental dosing. The PFAA precursors consistently decreased with an increasing dose, even without temperature involvement. Short-chain PFCAs and PFNA appear to accumulate in the samples with increasing eBeam doses, except for PFHpA (treated at 1000 kGy and 2000 kGy) and PFOS (treated at 2000 kGy). PFBS appeared to accumulate without temperature involvement in eBeam dosing.

In leachate, groundwater, and wastewater samples as well, the PFAS degradation increases with increasing eBeam doses between 500 kGy and 2000 kGy during incremental eBeam dosing. In leachate samples, compared to the eBeam treatment at 500 kGy, the decomposition efficiencies of PFOA increase 21% at 1000 kGy and 52% at 2000 kGy respectively. In general, the degradation of PFAS in the leachate samples increases as the eBeam dose is increased from 500 kGy to 2000 kGy even without the influence of elevated temperatures. Similar results were observed in the groundwater samples as well with increasing PFAS degradation as the eBeam dose was incrementally increased from 500 kGy to 2000 kGy. Since these studies were performed using actual PFAS-impacted environmental matrices, traditional mass balance calculations were not possible. However, we utilized PFOS-spiked buffer solutions to demonstrate the mass balance of total fluorine (6.34±0.86 µg) before eBeam treatment and total fluorine (7.30 ± 2.45 µg) after eBeam treatment. There was no dependance on matrix pH for PFAS degradation suggesting that at very high doses temperature is an extremely important factor. These experiments have unveiled previously unknown processes occurring in the samples during eBeam treatment. These results suggest that during high dose eBeam treatment of environmental matrices, PFAS is degraded by several mechanisms including

1. Decomposition of PFAS directly through the action of energetic electrons

2. Indirect degradation of PFAS through the formation of radiolytic species resulting from energetic electrons.

3. Degradation of PFAS caused due to the elevated temperatures resulting from exposure to high doses of electron beam irradiation

4. Degradation of PFAS resulting from the synergism between the direct and indirect impacts of energetic electrons at elevated temperatures experienced during high doses of electron beam exposure

We gained a mechanistic understanding of the eBeam-mediated degradation of short-chain PFAS (PFHpA) in distilled water. The results unequivocally demonstrate that aqueous electrons are accountable for the degradation of this molecule within eBeam doses ranging from 10 kGy to 80 kGy. PFHpA exhibited less than 10% degradation at pH 6.0. Defluorination and decarboxylation pathways predominated at these eBeam doses, and the eBeam degradation remained unaffected by the presence of bicarbonate, nitrate ions, or natural organic matter.

A transportable eBeam treatment platform was designed in silico. A truck mounted linear accelerator capable of delivering 2000 kGy to solid media could be developed if needed. This platform could be transported to various locations (waste water treatment plants) to demonstrate the utility of eBeam to degrade PFAS as well as other pollutants. The project has advanced our understanding of the technical and economic feasibility of the transportable eBeam platform.

Conclusions:

Overall, the project has provided conclusive evidence that high (2000 kGy) eBeam dose can achieve significant PFAS degradation in biosolids, composted biosolids, landfill leachates, wastewater effluent and groundwater. In addition to uncovering a previously unrecognized element of high eBeam dosing, namely the synergistic effect of high temperature and eBeam doses on PFAS degradation, this project has also advanced our understanding of the technical and economic feasibility of a transportable eBeam technology platform for demonstration purposes. Optimization of the dose and the design of a suitable treatment vessel to withstand the high temperature and resulting pressure will have significant commercial implications.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Publications Views
Other project views:	All 10 publications	4 publications in selected types	All 3 journal articles

Publications
Type	Citation	Project	Document Sources
Journal Article	Lassalle J, Gao R, Rodi R, Kowald C, Feng M, Sharma VK, Hoelen T, Bireta P, Houtz EF, Staack D, Pillai SD. Degradation of PFOS and PFOA in soil and groundwater samples by high dose electron beam technology. Radiation Physics and Chemistry 2021;189:109705.	R839650 (2023) R839650 (Final)	Full-text: ScienceDirect HTML Exit
Journal Article	Feng M, Gao R, Staack D, Pillai SD, Sharma VK. Degradation of perfluoroheptanoic acid in water by electron beam irradiation. Environmental Chemistry Letters 2021;19:2689-2694.	R839650 (2023) R839650 (Final)	Full-text: Springer - Full Text HTML Exit

Supplemental Keywords:

ionizing irradiation, electron beam, eBeam, PFAS, PFOS, PFOA, PFHpA, degradation, high energy, high dose, 2000 kGy, 500 kGy, 1000 kGy, linear accelerator, transportable, platform, temperature-enhanced PFAS degradation, eBeam dose

Relevant Websites:

National Center for Electron Beam Research TAMU Exit

Progress and Final Reports:

Original Abstract

The 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.