The purpose of this pilot-scale investigation was to validate the effectiveness and develop scale-up criteria for integrating a per- and polyfluoroalkyl substance (PFAS) treatment and destruction technology into existing groundwater treatment systems. This pilot study evaluated the effectiveness of the PFAS treatment train: ion exchange resin, resin regeneration, distillation of spent regenerant, and low energy plasma destruction of concentrated PFAS waste.

The goal of this project was to demonstrate the effectiveness of the proposed PFAS treatment train and provide guidance on how to integrate the treatment train into existing co-occurring chemical treatment systems. Specific technical objectives included:

• Measuring the effectiveness of PFAS and co-occurring chemical treatment during each step of the treatment train.
• Validating the technical approach at the demonstration-scale.
• Verifying waste minimization via resin reuse, regenerant reuse, PFAS concentration, and PFAS destruction.
• Based on field performance, developing guidance for applicability and limitations, anticipated performance, design considerations, and costing for integrating the investigated PFAS treatment train into existing co-occurring chemical treatment systems.

The pilot-scale PFAS treatment train consisted of four technologies that complemented each other to remove PFAS from treated water with reusable media, reduce the volume of the PFAS-impacted waste stream, and destroy that waste stream on-site:

• Ion exchange (IX) resin: PFAS removal from groundwater utilizing Sorbix HC1 regenerable ion exchange resin (HC1) resin.
• Regeneration: solvent solution using isopropyl alcohol (IPA) and sodium chloride used for removal of PFAS from IX resin to regenerate it for multiple groundwater treatment cycles.
• Distillation: recovery of used IPA solvent to be reused in future regenerations.
• Low-energy plasma destruction: PFAS destruction in the still bottoms, closing the loop for on-site removal, treatment, and destruction of PFAS.

Operation of a PFAS Treatment System: Pilot-Scale DMAX Plasma

The first performance objective for the pilot test was to demonstrate that the HC1 IX resin was able to consistently treat the incoming groundwater to levels at or below the EPA Lifetime Health Advisory (2016). The sum of analyzed PFAS remained at greater than 95% removal efficiency. The second performance objective for the pilot test was to demonstrate the successful reuse of regenerated IX resin over multiple loading cycles and recovery of the regenerant solution using distillation. The original HC1 resin loaded at the start of the pilot test remained in use for the duration of the test and continued to provide PFAS treatment effectively, meeting PFAS removal performance objectives. The performance objective for plasma destruction of the still bottoms was that all identified PFAS be below 70 ppt on an individual compound’s basis. All measured PFAS were below detection limits at the conclusion of treatment, exceeding the performance objective, except for PFBA.

The need for pre-treatment of influent water was understood at the outset of this pilot study as a requirement to effectively operate the system. As influent water quality and co-occurring chemicals will vary for each site, an appropriate pre-treatment design, bench testing, and operational optimization may be required. This PFAS Treatment Train can be integrated into existing groundwater treatment systems with co-occurring chemicals, typically after the existing treatment processes, as long as there is appropriate pre-treatment of the influent water prior to the PFAS Treatment Train.

The findings from the pilot study have been used to develop a cost model for regenerable IX/distillation/plasma scenario to be used as a comparison to other currently available technologies. While each of the PFAS treatment technologies has its advantages and disadvantages, and while it remains true that site specific conditions will generally determine which treatment alternative is selected, some key takeaways from this project can be made that will help in the decision framework:

• Regenerable IX with onsite destruction will be most attractive in high groundwater concentration PFAS source areas with long treatment horizons.
• Single pass media will be most effective and practical in low to moderate PFAS concentration groundwater plumes or wellhead treatment for water supply.
• Whether regenerable IX will have lowest life cycle cost depends on the relative O&M costs, which can vary significantly based on the site conditions and location. If the O&M for regenerable IX is higher than single pass, regenerable IX will be the most expensive option throughout the project life cycle. In these cases, regenerable IX still represents the lowest waste and liability technology and may be preferred for that reason.

In general, this technology appears to have good performance and can be cost competitive with other currently available technologies depending on individual site-specific requirements.

The following issues are presented to help with additional design considerations:

• Pretreatment for co-occurring chemicals. Based on the site-specific co-occurring chemicals, pretreatment requirements can add to increased building size and larger pretreatment vessels footprint. These need to be carefully evaluated prior to design of any full-scale system.
• Down-flow versus up-flow operation of the resin beds and the ability to backwash as required. Any full-scale system should be down-flow to allow backwashing to remove fouling from the media. Based on the pilot- and full-scale observations, the treatment system should be fitted with down-flow and up-flow valving to reduce operations and maintenance costs.
• Biofouling can be observed in any IX/granular activated carbon (GAC) system, especially during long periods of down time required by maintenance activities, leading to pressure drop. Treatment equipment should include provisions for addressing these issues (backwashing and/or biocide addition) that could possibly negatively affect the resin/GAC performance.
• Consider the use of single pass IX after regenerable IX if the influent stream has short-chain PFAS that require removal to meet regulatory requirements. Alternatively, the regeneration cycle length can be reduced to accommodate enhanced removal of short chain PFAS.
• Waste minimization may be reduced if pretreatment before regenerable IX and tertiary treatment after plasma destruction are required. These wastes could potentially include spent filters, sludge, and spent media requiring disposal as PFAS containing wastes.
• If regeneration and distillation cannot be performed outside (dependent on geographical system location) the equipment building, equipment, and appurtenances must be explosion proof.

(Project Completion - 2023)

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