Grantee Research Project Results

Final Report: Plasma-driven Destruction of PFAS in Complex Water Matrices

EPA Contract Number: 68HERC24C0010
Title: Plasma-driven Destruction of PFAS in Complex Water Matrices
Investigators: Groele, Joseph
Small Business: Fourth State LLC
EPA Contact: Richards, April
Phase: I
Project Period: December 1, 2023 through May 30, 2024
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2024) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , PFAS Treatment , Water Treatment

Description:

The evidence linking per- and polyfluoroalkyl substance (PFAS) exposure to adverse health consequences has continued to accumulate over the years, and with the National Primary Drinking Water Regulation released by the EPA in April 2024, actionable regulations have been finalized. In response, the market interest in technologies that can remove PFAS from waters is higher than ever. Technologies that can destroy PFAS rather than simply moving them into different media are desired to avoid the generation of secondary waste streams and management of PFAS-laden materials associated with absorptive/separative treatment processes. Direct destruction of PFAS in waters also mitigates the risk of reintroducing PFAS into the environment.

Plasmas have been demonstrated to be highly effective at destroying PFAS, but as with all emerging PFAS destruction technologies, scaling up the process to cost-effectively treat commercially significant flow rates remains a challenge. Furthermore, due to the surface-process nature of plasma-based treatments, destruction of short-chain PFAS which have less affinity for the gas-liquid interface presents another challenge. Fourth State is developing a plasma-based approach that features an innovative geometric configuration to optimize the plasma-liquid interface and leverage turbulent flow to effectively destroy both long- and short-chain PFAS without the use of chemical consumables—only electricity is needed. The patented Fourth State plasma reactor technology offers an environmentally friendly approach to destroy PFAS with competitive energy costs and with no secondary waste streams. The technology demonstrated effective PFAS decomposition in a range of different waters, including spiked samples, groundwaters, and landfill leachates.

This SBIR Phase I project focuses on the destruction of PFAS in complex water matrices. Here, landfill leachate is selected as the complex water matrix for study, as it contains a range of co-occurring contaminants, including PFAS, in addition to high concentrations of organic compounds, heavy metals, ammonia, humic substances, and other emerging contaminants that may act as scavengers of plasma-derived reactive species which drive the destruction of PFAS. By improving our understanding of plasma treatment in such complex water matrices, the markets to which this technology may be applied significantly expand to include landfill leachates, groundwaters, industrial wastewaters, and concentrates from separative treatment processes (e.g., reverse osmosis). Meanwhile, the challenge of scale-up is being addressed by a separate, but parallel and synergistic research activity, which will use kinetics information from the batch-mode PFAS destruction experiments to inform the reactor scale-up to process throughputs exceeding 50 gallons per minute.

The overall objective of this Phase I activity is to demonstrate that the plasma reactor is capable of decomposing both long- and short-chain PFAS in landfill leachate, a real-world complex water matrix containing a range of co-contaminants and scavenger species. In the process, PFAS removal rates will be evaluated and used to inform the scale-up to larger treatment volumes. First, a new plasma reactor was constructed based on the design of an existing bench-top research reactor but with a larger reservoir for handling larger process volumes and a larger pump for achieving higher recirculation flow rates.

Summary/Accomplishments (Outputs/Outcomes):

Initially, methylene blue was tested as a model contaminant to ensure that the plasma generated in the new reactor was producing reactive species for driving contaminant decomposition, and the impact of recirculation flow rate was assessed. For a given treatment time, higher recirculation flow rates provide a faster decay of methylene blue, but it is not completely clear whether this effect is primarily related to the increased number of times that the volume of water passes through the plasma discharge region, if it is related to the water jet structure becoming more turbulent in the discharge region, or a combination of both. The effects of recirculation flow rate and Reynolds number in the plasma region will continue to be investigated in subsequent research activities.

Next, water samples spiked with perfluorooctanesulfonic acid (PFOS) at two different concentrations (40 ppb and 140 ppt) were processed with the plasma reactor. At a recirculation flow rate of 11.3 L/min, rapid decomposition of PFOS was observed before leveling off at approximately 75% removal after six minutes of treatment. This leveling off behavior was not expected since previous experiments have resulted in PFOS removal to below 1 ppt (below detection limit). The cause is still being investigated, but it is suspected that localized flow stagnation introduced by the new baffle system may have been limiting the ultimate PFOS removal percentage, and the baffle system is being redesigned to address this. Regardless, the energy efficiency for PFOS removal in this test is competitive with an electrical energy per order (EE/O) value of 21 kWh/m3.

A sample of landfill leachate was collected from a confidential site and processed by the plasma reactor. Overall, the results are promising, indicating significant reductions in PFAS concentrations for both long- and short-chains. Thus, the plasma reactor demonstrated the capability to decompose PFAS in the complex water matrix of the landfill leachate. Notably, 48% of the long-chain and highly ubiquitous perfluorooctanoic acid (PFOA) was removed, as well as 62% of perfluorohexane sulfonate (PFHxS). As for short-chains, 24% of perfluorobutane sulfonate (PFBS), 70% of perfluorohexanoic acid (PFHxA), 70% of perfluoroheptanoic acid (PFHpA), and 63% of perfluoropentane sulfonic acid (PFPeS) were removed. With approximately 130 W of power deposited into the plasma, the total energy deposited into the plasma was estimated at 0.39 kWh over the 3 h treatment duration. PFAS precursors, although not present at high concentrations in the leachate, were also removed, including 100% of 4:2 fluorotelomer sulfonic acid (4:2 FTSA), 68% of 6:2 fluorotelomer sulfonic acid (6:2 FTSA), 68% of 8:2 fluorotelomer sulfonic acid (8:2 FTSA), and 100% of n-ethyl perfluorooctane sulfonamidoacetic acid (EtFOSAA). Therefore, the plasma technology being developed by Fourth State not only addresses the compounds currently included in EPA’s National Primary Drinking Water Regulation, but also addresses the various short-chain PFAS and precursors that are not currently included in this regulatory criteria that could transform into long-chains and which may later be linked to adverse health consequences themselves.

Conclusions:

Overall, we consider the leachate test to be a successful demonstration of feasibility and a promising Phase I result, but there is still work to be done to optimize the treatment process to reach EPA’s National Primary Drinking Water Regulation maximum contaminant levels and improve the energy efficiency. Moving forward, we will be engaging with landfill owners and operators to acquire additional samples for testing to better understand the removal rates for PFAS in the range of different water matrices encountered in the field. Simultaneously, we will continue to scale-up the treatment process to accommodate commercially significant throughputs. We plan to collaborate with engineering consultancies to set up a pilot-scale demonstration system and ultimately integrate our technology into full-scale treatment systems.

SBIR Phase II:

Plasma-driven Destruction of PFAS in Complex Water Matrices: Pilot-scale Demonstration