Grantee Research Project Results

Final Report: In Situ Remediation Technology (InSRT) for Remediation of PFAS Contaminated Groundwater

EPA Contract Number: 68HERC20C0021
Title: In Situ Remediation Technology (InSRT) for Remediation of PFAS Contaminated Groundwater
Investigators: Laramay, Fiona
Small Business: RemWell, LLC
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2020 through August 31, 2020
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2020) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Clean and Safe Water

Description:

Per- and polyfluoroalkyl substances (PFAS) are a group of 5,000 (or more) fluorinated organic contaminants. PFAS have been used in consumer products and in fire-fighting foams which have been used globally, contaminating air, water, and soil. The potential for widespread exposure is a concern because PFAS may cause multiple cancers, as well as other diseases, even at part-per-trillion concentrations. To date, remediation of PFAS contaminated groundwater has occurred ex situ because of availability of remediation methods for PFAS. In situ remediation is desirable because contaminants remain in place, reducing risk, and energy is not expended to pump contaminated water in and out of the aquifer.

RemWell's in situ Reactor Technology (InSRT) operates in situ and uses sonolysis to break down PFAS molecules. A horizontal remediation well is used to capture contaminated groundwater. Water preferentially flows through the well rather than the aquifer, thus channeling water into the well. Once in the well, the water flows through InSRT where it is treated by ultrasound (sonolysis). When applied to liquids, ultrasound creates cavities which rapidly collapse, creating high-temperature and pressure conditions. PFAS partition to the cavity interface, prior to collapse, and are exposed to the extreme collapse conditions, causing the PFAS molecules to break down.

The Phase I project focused on developing a functional design for InSRT for field demonstration and use. Previous work focused on evaluating the effectiveness of the reactor for PFAS degradation in spiked samples and groundwater, and theoretical assessments of feasibility and sustainability. The results of the previous work were helpful to determine if the InSRT reactor was a promising technology. In Phase I, the objectives in the table (below) were addressed to prepare InSRT for field demonstration.

Table 1. Shows the five objectives addressed to prepare InSRT for field demonstration

Questions	Objectives
Can InSRT's ultrasond transducer be effectively isolated from sources of water and moisture?	1. Develop final design for in situ reactor housing 2. Perform comprehensive reactor leak testing
Can InSRT be readily and simply be deployed and operated?	3. Field test InSRT deployment and evaluate ease of implementation
Can water flow through the reactor be controlled to allow for a specified reactor retention time?	4. Conduct in-well operational testing 5. Conduct in-well flow control testing

The following tasks were completed to support the objectives described in the table:Table 1. Shows the five objectives addressed to prepare InSRT for field demonstration.

Task One. Develop final design for in situ reactor housing.

Task Two. Perform comprehensive reactor leak testing

Task Three. Field test InSRT deployment and ease of implementation

Task Four. Conduct in-well operational testing

Task Five. Conduct flow-control testing

In Task One the laboratory design was extended for field use which included identification of a reactor housing material, leak-free seals, and design and testing of flow funnels. The latter are used to connect the reactor tank to the housing cylinder and control flow of water into the tank. Leak testing was completed in Task Two on the design resulting from Task One. In Task Three, the ease and repeatability of assembly and insertion of the reactor were completed, and an assembly manual written to document the process. In Task Four the reactor was installed in a test pit to evaluate operation of the transducer underground. Finally, in Task Five, flow control tests were proposed. The hydraulic retention time will vary between sites and the ability to control the velocity of water through the reactor will be necessary.

Summary/Accomplishments (Outputs/Outcomes):

Task One: In Task One, a reactor assembly was designed around the reactor tank and specifications for a 12-inch diameter well. The design goals included: (1) all seals do not leak, and (2) excess weight is minimized, using as few parts as possible and using commercially available components wherever possible. The final assembly (shown in Figure 1) consisted of a 12-L (approximately) tank where the contaminated water is treated.

Figure 1. Complete reactor assembly prior to insertion into housing cylinder. A) Tank B) transducer cover C) funnels.

On one face of the tank, an ultrasonic transducer plate is attached which is connected to a generator. The tank is open on each end and a funnel is attached at either end, extending from the tank opening to the housing cylinder. The cylinder is a PVC or HDPE tube in which the assembly is contained. A cover is placed over the transducer board and has one hole for the RF cable to extend through.

The final design included updates from versions early on in Phase I by creating a curved cover and tank base to better utilize space in the well. The cover design can also be modified to accommodate different RF cable configurations, if needed. Seal materials were also identified that would be viable for the reactor, particularly a high temperature silicone rubber that was also used in laboratory operational tests. The project schedule was subject to Covid-19 interruptions and many tasks reshuffled as needed to continue making progress. Some interim designs from Task One went through Task Two leak tests to identify areas of weakness in the overall design.

Task Two: Leak tests were completed in Task Two on one or more parts of the assembly, depending on the specific question to answer. For example, when testing new gasket materials on the tank, the rest of the reactor was not assembled. Complete assembly leak tests were also performed over the course of the project with variable results. Many sealing mechanisms were eliminated included commercial tapes, glues, and caulking products. The best alternative was a gasket bolted down at an interface. Alternatively, future iterations could weld more parts together to reduce the number of seals, though that might minimize potential for reuse. An interim design used in Task Four was later found to have leaks around the outside of the tank which resulted in additional design changes. The design in Task One was completed when all water leaks were fixed.

Task Three: Task Three was completed three times; once to identify initial issues in the process (e.g. where the RF should pass through, which components did not seal well together), the second while preparing for field installation, and the third with the final design. The first trial revealed that sealing the housing cylinder to the well casing would be challenging because any seal could only be semi-permanent for eventual removal and replacement of the reactors. The reactor would be slid down into the well before the gap could be sealed and therefore would not be directly accessible for sealing. An inflatable ring meant for sealing a similar gap was ordered and tested but was not viable. However, an expandable mechanism would be valuable during installation and removal, but a different product is needed. A semi-rigid rubberized material is proposed to interface the housing cylinder and well casing. The design will be best realized in a well with separate entry and exit points. The next assembly test identified that the angle proposed in the funnel design was crucial to successful installation because of the cover height which makes the total diameter of the assembly unevenly split across the total height of the assembly components. The final test was successful, which can be attributed to design ideas from a single manufacturer of the assembly who we are now working with and will continue to work with moving forward (previously multiple manufacturers were involved). Each component was readily assembled with common hardware and interfaced well with the housing cylinder.

Task Four: In-well operational testing was attempted in Task Four but two key challenges were encountered and are explained first, followed by lessons learned and adaptations made. The task was to be completed in a preexisting test aquifer composed of gravel influent and effluent and packed in between with a clean sand media. The volume was approximately 2,000 gallons, lined with a pond liner. Old material from the pit was excavated with care to prevent damage to the liner. Nonetheless, after several attempts and tests to fill the pit and maintain the water level, it was concluded that the liner was ripped. For example, at one point in just 12 hours more than 2 feet of the water depth was lost at the effluent end. The water loss did not eliminate the possibility of continuing Tasks Four or Five but added complications. Before attempting any flow control or pumping tests for Task Five, it was decided the reactor should simply be turned on in situ in order to verify it was working before continuing to modify the setup for pumping tests. At that point it was discovered that, while the reactor was successfully turning on, the power levels could not be maintained during multiple tests. The changing levels either meant one or more wires was poorly connected, or water had leaked onto the electrical components. After multiple attempts to complete the tests and thoroughly checking the external setup, the reactor was dug up and disassembled. After inspection it was determined that the last-minute changes to the flow funnel attachments had caused water leakage. The flow funnels used were constructed from waterproofed foam and duct work. In the lab tests the simple prototype was viable but the design, however, did not allow for the cover height such that the funnels were subsequently adjusted and resealed at the last minute. The end result was that the water circumvented either the funnels or the tank gaskets and leaked onto the board, interrupting the flow of electricity during testing. The tests did demonstrate that the reactor can operate in situ but did not demonstrate the outcome of operation for more than 2 minutes at a time. At this point the remainder of Tasks Four and Five were not pursued in favor of having a fully developed assembly (described above) for use in additional field demonstrations (i.e., additional design and leak-testing iterations).

Conclusions:

Many important lessons were learned along the way that lead to a promising design for field implementation for Phase II. Individually, the tasks completed during Phase 1 were important opportunities for further technical development, and the small-scale field testing completed was an important interim step before pilot testing. Despite experiencing several unanticipated challenges during Phase I, the overall purpose of the design was supported. The funnels bridged the gap from reactor housing to the well casing while funneling water into the tank. The cover was updated to provide protection to the transducer while maximizing the use of space in the assembly. The final updated, leak-free assembly to be used in future field demonstrations is successful because the electronics will not be in contact with water. The assembly also achieves the purpose of flowing PFAS-contaminated water into the reactor in a controlled manner. Additional work proposed for Phase II will include extensive field tests, which will further accelerate RemWell toward the first reactor sale.

No sales have resulted from Phase I. Instead, RemWell has co-proposed an Environmental Security Technology Certification Program (ESTCP) project to the U.S. Department of Defense and is proposing an EPA Phase II SBIR project. The combination will get RemWell through field testing and to be ready for the first customer. Some of Phase I was spent developing a marketing plan, a business plan, and beginning to assemble due diligence documentation should venture capital be sought in the future.

Supplemental Keywords:

 

SBIR Phase II:

In Situ Remediation Technology (InSRT) for Remediation of PFAS Contaminated Groundwater  | Final Report