2024 Excellence in Environmental Engineering and Science™ Awards Competition Winner

Superior Achievement

Category Entered: Research

From the Laboratory to the Field - STAR Treatment of PFAS in Soils

Entrant: Savron, a division of Geosyntec Consultants International, Inc.
Engineer in Charge: n/a
Location: Cambridge, Ontario, Canada
Media Contact: David Major, Ph.D., BCES

Entrant Profile

Savron is an operating division of Geosyntec Consultants International, Inc., and is a multi- national provider of sustainable waste management and remediation solutions specializing in the safe, energy-efficient, environmentally responsible treatment of a broad range of hazardous materials. Savron helps oil and gas, waste management, chemical manufacturing, and federal clients manage their environmental liabilities and comply with regulatory requirements.

The STAR process is based on an energy-efficient, self-sustaining smoldering combustion process that captures and recycles the energy released from organic contaminants to destroy them effectively, controllably, and safely. A broad range of hazardous materials, including petroleum hydrocarbons, coal tar, and creosote can be treated by our technology.

Savron, the University of Western Ontario, Royal Military College of Canada, Brown University, and the University ofNotre Dame explored how to use STAR to destroy polyfluoroalkyl substance (PFAS) in soils. As PFAS are not contaminants that can support smoldering combustion in and of themselves, a surrogate fuel is required. Numerous fuel surrogates are viable; however, low concentrations of spent or fresh granular activated carbon (GAC) can be used to generate the high temperatures required for PFAS destruction. When spent GAC is used then two problems can betreated concurrently: waste GAC and PFAS-contaminated soils. Laboratory studies were used to verify the destruction of PFAS and fluorine mass balance and to optimize PFAS mineralization with minimal production of by-products. A fieldprogram using Savron’s 10 m3 pilot HottPad™ system demonstrated successful treatment of PFAS-impacted soils at a Canadian Forces Base located in Ontario.

Project Description

Background

Smoldering is a flameless, heterogeneous, exothermic oxidation reaction that occurs on the surface of a solid or liquid fuel that oxygen penetrates. Smoldering can be self-sustaining after a one-time, local ignition event, provided that the heat generated by oxidation overcomes heat losses to the surrounding environment. After ignition, the smoldering reaction front propagates from the ignition point through the porous medium in the direction of convective airflow.

Smoldering combustion to treat hydrocarbon contamination has been applied at full scale to treat contaminated sites. For hydrocarbon-contaminated materials, the contaminant acts as fuel. Generally, liquid hydrocarbons (e.g., crude oil) will achieve smoldering temperatures ~500°C. Although PFAS can be volatilized and partially broken down to form shorter-chain length PFAS and volatile organic fluorine (VOF) compounds at relatively low temperatures (400-500°C), and be partially defluorinated at 700°C, a higher degree of destruction and mineralization require temperatures greater than 900°C. However, treating PFAS by smoldering requires adding a supplementary fuel as typical PFAS concentrations in soils (ng to μg per kg) are too low to serve as a smoldering fuel.

Our laboratory column studies demonstrated:

1. Adding GAC at low concentrations (35 g GAC/ kg soil) supported temperatures greater than 900˚C
2. Essentially all the PFAS mass ( >99.9%) was removed from the soil, based on PFAS analysis and tracking the fate of fluorine (as hydrogen fluoride [HF] or as shorter chain VOF).
3. Adding calcium oxide (CaO) at low concentrations enhanced the mineralization of PFAS and the formation of calcium fluoride (CaF2), thereby removing HF from the emissions.

Our field demonstration involved treating two 10 m3 batches of contaminated field soil with unknown PFAS species and concentrations at a Canadian Forces Base in Ontario. The soils were treated in a pilot HottPad™ system consisting of a walls, a swing door, a retractable emissions capture hood, and a trafficable base equipped with a series of heaters and an air distribution system to support the smoldering combustion reaction. Soils were mixed with GAC and CaO and placed within the HottPad. After ignition, the smoldering process was monitored through thermocouples placed vertically in the soil pile and the production of combustion gasses (carbon dioxide and carbon monoxide). The emissions were extracted under vacuum and directed to vapor-phase GAC vessels. The emissions were also sampled for HF and VOF. The pre and post-treatment soils were sampled for PFAS and presence of CaF2. The field pilot demonstrated the same results as the columns studies, namely:

1. Greater than 99.9% reduction in PFAS concentrations and below regulatory criteria
2. ~ 0.2% of the fluorine mass was detected in the emissions (as organic fluorine), with the fluorine being associated with CaF2 trapped on the treated soil.
3. Targeted and Non-Targeted analysis of gas samples demonstrated that any VOFs that emitted could be trapped by vapor phase GAC treatment.

Integrated Approach to Environmental Media

The results of the study demonstrated that along with treating PFAS in soil below current advisory levels, there was no or minimal release of VOF or HF into the air. Treated soils can be reused for fill and can still support plant growth with minimal manipulation. The technology can also be used to treat waste GAC and, therefore, treat waste that is produced by water treatment technologies. Furthermore, any VOF or PFAS emitted during smoldering can be captured by vapor phase GAC, which could be used as fuel to smolder other PFAS-impacted soils.

Quality

This project was conducted under the U.S. Department of Defense Strategic Environmental Research and Development Program (SERDP), Project ER18-1593. This project and team received the SERP-ESTCP project of the year award for environmental restoration (https://demo.serdp-estcp.mil/newsitems/details/00857592-b81a-4080-b63a-29a4d5ab0bf5/demonstration-of-smoldering-combustion-treatment-of-pfas-impacted-investigation-derived-waste). This prestigious award speaks the impact and quality of this project.

Contributions to Social and Economic Advancement

Our technology addresses one of the most pressing and emerging contaminants; the “forever chemicals” that are increasingly found in the environment. PFAS has attracted considerable attention in the industry and community. The US Congress passed recent legislation (H.R. 2497) that directs the US Environmental Protection Agency (EPA) to designate two PFAS compounds - perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and to determine if the remaining PFAS should also be designated as hazardous substances. There are few available technologies that can treat PFAS in soils. Incineration is expensive, requires transporting the soils to fixed facilities, and has a large carbon footprint. Landfills are increasingly refusing acceptance of PFAS-contaminated soils and does not offer a permanent solution. Our solution has a lower carbon footprint, allows on site treatment, and its effective destruction of PFAS further removes the risk of the release of PFAS into the environment, eliminating future liability.

Originality and Innovation

Creativity and innovation are required to conduct laboratory studies that lead to a clear understanding of the smoldering process on the fate of PFAS, and then translate that knowledge to conducting a practical field demonstration that proves out the technology and collects key design and operational information.

Our work resulted in groundbreaking understanding of PFAS destruction through smoldering processes. This includes fully understanding the fate of fluorine to demonstrate mass balance of destruction (where did the PFAS go?). This work produced two Master theses, peer-reviewed publications, and presentations at several technical conferences as shown below:

Duchesne, A.L., Brown, J.K., Patch, D.J., Major, D., Weber, K.P., and Gerhard, J.I. 2020. Remediation of PFAS-Contaminated Soil and Granular Activated Carbon by Smoldering Remediation. Environmental Science & Technology. 54(19), 12631-12640.

Kinsman, L., Major, D., Grant, G., Duchesne, A., Harrison, B., Brown, J., Gerhard, J., Patch, D., Weber, K. 2021. Smouldering Remediation of PFAS-Contaminated Soils. SMART Remediation, Virtual Event, 18 February.

Kinsman, L., Major, D., Grant, G., Scholes, G., Duchesne, A., Brown, J., Harrison, B., Gerhard, J., Patch, D., Weber, K., McRae, C., Tam, A. 2021. STAR and STARx – Smouldering Remediation of PFAS-Impacted Soils. RemTech: Remediation Technologies Symposium, Banff, Alberta, Canada, 13-15 October.

Kinsman, L., Major, D., Grant, G., Scholes, G., Harrison, B., Brown, J., Gerhard, J., Patch, D., Weber, K., McRae, C., Tam, A. 2022. STAR and STARx – A Smouldering Solution to PFAS from Laboratory to Field Scale Application. RemTech: Remediation Technologies Symposium, Banff, Alberta, Canada, 12-14 October.

Kinsman, L., Major, D., Grant, G., Harrison, B., Gabayet, J., Brown, J., Gerhard, J., Patch, D., Weber, K. 2023. STAR and STARx: A Smouldering Solution to PFAS from Laboratory to Field Scale Application. RemTech Europe, Virtual Presentation to Ferrara, Italy, 18-22 September.

Kinsman, L., Major, D., Grant, G., Scholes, G., Harrison, B., Brown, J., Gerhard, J., Patch, D., Weber, K., McRae, C., Tam, A. 2023. STAR and STARx – A Smoldering Solution to PFAS from Laboratory to Field Scale Application. RemTEC & Emerging Contaminants Summit, Westminster, Colorado, 3-5 October.

Liefl, D., Major, D., Grant, G., Scholes, G., Ferguson, W., Kinsman, L., Harrison, B., Brown, J., Gerhard, J., Patch, D., Weber, K., McRae, C., Tam, A. 2023. STAR and STARx – A Smouldering Solution to PFAS from Laboratory to Field Scale Applications. International In-Situ Thermal Treatment (i2t2) Symposium: Remediation & Recovery, Banff, Alberta, Canada, 17-18 May.

Major, D., Duchesne, A., Brown, J., Gerhard, J., Patch, D., Weber, K., Reynolds, D., and Grant,

G. 2019. PFAS Destruction in Soil and Investigation Derived Wastes through SmolderingCombustion. RemTEC & Emerging Contaminants Summit, Denver, Colorado, 26-28 February.

Major, D., Gerhard, J.I., Duchesne, A.L., Reynolds, D.A., Brown, J. Grant, G.G., Weber, K., Patch,

D. 2019. PFAS Destruction through Smoldering Combustion. RPIC Federal Contaminated Sites Regional Workshop, Halifax, Nova Scotia, Canada, 4 June.

Major, D. 2019. PFAS Destruction through Smoldering Combustion (STARx). SERDP & ESTCP Webinar Series, Webinar #103, 7 November.

Major, D., Duchesne, A., Brown, J., Gerhard, J., Patch, D., Weber, K., Reynolds, D., and Grant,

G. 2020. A Smoldering Solution to PFAS. RemTEC & Emerging Contaminants Summit, Westminster, Colorado, 10-11 March.

Major, D. 2020. A Smouldering Solution to PFAS. EcoForum, Virtual Event, 18 September.

Major, D. 2021. Closing the PFAS Mass Balance for Smoldering. RemTEC & Emerging Contaminants Summit, Virtual Event, 9-11 March.

Major, D., Duchesne, A., Brown, J., Gerhard, J., Patch, D., Weber, K., Reynolds, D., Grant, G., 2021. PFAS Destruction through Smoldering Combustion (STARx). RPIC Federal Contaminated Sites Regional Workshop, Virtual Event, 15-18 November.

Scholes, G., Grant, G., Major, D., Gerhard, J., Duchesne, A., Brown, J., Weber, K., and Patch, D. 2019. Smouldering Combustion for the Management of PFAS-Impacted Soils at Brownfields Redevelopment Sites in Canada. RemTech: Remediation Technologies Symposium, Banff, Alberta, Canada, 16-18 October.

Complexity

Since the field demonstration, we have improved the pilot HottPad system to make it larger but even simpler to construct, ship, and operate on-site. The Department of Defense Innovation Unit (DUI) has selected our new system for demonstration in Alaska at Joint Base Elmendorf- Richardson. Our design allowed delivering the entire HottPads and ancillary / control equipment by truck or rail, with minimal site preparation to set up.

Contaminated soil can be excavated and mixed with GAC/CaO by a backhoe before placement in the HottPad. Thermocouples monitored temperatures in the soil piles and HottPad plenum space. The retractable roof is cantilevered to allow single-person opening and closing. Combustion gases are collected via an extraction pipe and continuously monitored and treated before discharge through vapor GAC treatment. Treated soils were easily removed via backhoe/bobcat before being reloaded with the next batch.

Click images to enlarge in separate window.

Column Experiments Small columns were used to demonstrate the mineralization of PFAS under differing smoldering conditions and in the presence of CaO and to obtain a mass balance of organic fluorine (a measure of the fate of PFAS) CaO enhances the thermal decomposition of PFAS to HF and CO2. 100% of the gas was captured and directed to an HF trap (EPA Method 26) and to a PFAS/VOF trap (as per Duchesne et al 2021). In addition to analytical measurement of PFAS in soil and in the PFAS/VOF traps, the higher concentrations of PFAS used in the column tests allowed use of PIGE (particle induced gamma emission) spectroscopy to quantify fluorine.
Intermediate Scale Reactor (ISR) ISR was used to demonstrate scaling of the small scale column experiments to account for soil heterogeneity. Field soils from the Canadian Forces Base were used. A convective heater is used to inject hot air in a plenum space located at the base of the ISR. Site soils were mixed with GAC and CaO and added to the ISR. After a short heating period to initiate smoldering, the heater is turned off while air supply is maintained. The energy from smoldering GAC provided all the energy needed to maintain a self-sustaining combustion reaction. Separate sampling streams were used to capture any released HF and VOF.	PFAS Contaminated Soils Soils that were excavated from a Fire Training Area and contaminated with PFAS were stored in piles that were placed on and covered with geotextile liners. The liners were opened and soils excavated for the Pilot Tests
HottPad™ Pilot Test This figure shows the set-up of the pilot test. The Pilot HottPad™ is on the right showing the extraction hood pulled back. The extraction lines passed through a knockout tank before entering the trailer that contains the control and monitoring equipment (temperature and combustion gasses)	Soil Mixing This figure shows batches of excavated soil being mixed with GAC and CaO using a bobcat and excavator. The white stain on the soil is CaO. The soils were mixed until visual observation indicated that the GAC and CaO were uniformly mixed. Soil samples were collected for PFAS analysis prior to adding the GAC and CaO
HottPad Loading This figure shows loading of the mixed soils into the HottPad This map shows the regions in the nation which are not meeting the standards for ozone, and there are only two regions which are in extreme nonattainment, and they are both located in California which are the South Coast Air Basin and San Joaquin Valley. And Tulare Lake Compost is located right in the middle of one of them. What this means is the local air district must closely regulate emissions to reduce pollutant levels.
HottPad Loading This figure shows the final loading of the HottPad™. A limestone cap (~12 inch) was placed on top of the loaded soil as a protective layer to absorb HF if it was released. Beneath the limestone cap was the sampling lines for HF and VOF/PFAS emissions collection. Thermocouples were installed vertically through the soil pile and within the cap.	HottPad Operation This figure shows the HottPad™ with an additional cover to ensure vapor capture. Temperature and combustion gasses were continuously monitored. Emissions were collected beneath the cap and directed to HF and VOF/PFAS traps. Gas was also collected into a Silonite canister for targeted and non-targeted PFAS analysis.
Post Treatment This figure shows the soils after treatment. The soils are dry and show reddish color associated with oxidation of the iron in the soil. Soils were sampled for PFAS analysis, and for the presence of CaF2
Post Treatment Results This figure shows the concentration of PFAS pre and post treatment for both pilot tests. The concentration of individual PFAS post-treatment were below regulatory criteria. Converting the individual PFAS to organic fluorine equivalent and correcting for the mass of soil in each pilot test yields ~21,000 mg and 19,000 mg of organic fluorine in the first and second pilot tests, respectively. Approximately 0.2% of the initial total organic fluorine was found on the VOF/PFAS traps for each pilot test. Similarly, only ~0.5 mg of the total organic fluorine mass was found associated with trapped HF. The total organic fluorine mass remaining on the treated soils was ~16 and 0.2 mg for each test. The total organic fluorine associated with emissions or still present on the soil was ~2% of the initial organic fluorine mass. The other 98% of organic fluorine is associated with the formation of CaF2 that is an inert mineral phase on the treated soils.

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