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==PFAS Toxicology and Risk Assessment==  
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==Thermal In Situ Sustainable Remediation to Enhance Biotic and Abiotic Reactions and Accelerate Remediation Timeframes==  
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This article presents an overview of current practices for human health and ecological risk assessment related to [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and poly-fluoroalkyl substances (PFAS)]] exposures at [[Wikipedia: Firefighting foam | aqueous film-forming foam (AFFF)]] impacted sites.
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Thermal In Situ Sustainable Remediation (TISR<sup>®</sup>; US Pat. Nos. 10,384,246 and 10,688,545) is a cost-effective and adaptable low temperature thermal remediation technology that accelerates contaminant treatment. It achieves this by enhancing biotic and abiotic contaminant degradation rates through a modest increase in subsurface temperature. TISR<sup>®</sup> is suitable for a wide range of hydrogeologic settings. It also offers reduced operational costs, a lower carbon footprint, and possibly shorter remedial timeframes than more conventional methods.
 
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'''Related Article(s):'''
 
'''Related Article(s):'''
  
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*[[Thermal Remediation]]
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*[[PFAS Sources]]
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*[[Thermal Remediation - Electrical Resistance Heating | Electrical Resistance Heating]]
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*[[PFAS Transport and Fate]]
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*[[Thermal Conduction Heating (TCH)]]
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*[[Thermal Remediation - Combined Remedies | Combined Remedies]]
  
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'''Contributors:''' Jennifer Arblaster, Jason Conder, Jean Zodrow and Elizabeth Nichols
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'''Contributors:''' Jonah Munholland, Julia Vidonish, and Craig Divine
  
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'''Key Resource(s):'''
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'''Key Resources:'''
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*State of the Science for Risk Assessment of PFAS at Contaminated Sites<ref name="ZodrowEtAl2021">Zodrow, J., Arblaster, J., Conder, J., 2021. State of the Science for Risk Assessment of PFAS at Contaminated Sites. In: ''Forever Chemicals: Environmental, Economic, and Social Equity Concerns with PFAS in the Environment'', Kempisty, D., Racz, L., (Ed.s). pp. 161-186. CRC Press. [https://doi.org/10.1201/9781003024521 doi: 10.1201/9781003024521]</ref>
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*Thermal In Situ Sustainable Remediation to Enhance Biotic and Abiotic Reactions and Accelerate Remediation Timeframes, Final Report. ESTCP Project ER20-5028<ref>Divine, C., Munholland, J., Zardouzian, E., Justicia-Leon, S., Aspinall, J.V., Randhawa, D., Falta, R., Freedman, D., Becker, M., 2025. Thermal In Situ Sustainable Remediation to Enhance Biotic and Abiotic Reactions and Accelerate Remediation Timeframes, Final Report. Environmental Security Technology Certification Program (ESTCP), Project ER20-5028. [https://serdp-estcp.mil/projects/details/bab4bc87-b4bc-42df-ad0e-11ea0adf27dc/er20-5028-project-overview Project Website]&nbsp; [[Media: ER20-5028 FR DevineEtAl2025.pdf | Final Report.pdf]]</ref>.
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*[https://itrcweb.org/ Interstate Technology Regulatory Council (ITRC)], [https://pfas-1.itrcweb.org/ PFAS – Per- and Polyfluoroalkyl Substances]
 
  
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==PFAS Exposure and Conceptual Site Models==
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*Advances in Low-Temperature Thermal Remediation. Munholland ''et al.'', 2024<ref name="MunhollandEtAl2024">Munholland, J, Rosso, D., Randhawa, D., Devine, C., Pennington, A., 2024. Advances in Low-Temperature Thermal Remediation. In: García-Rincón, J., Gatsios, E., Lenhard, R.J., Atekwana, E.A., Naidu, R. (eds), Advances in the Characterisation and Remediation of Sites Contaminated with Petroleum Hydrocarbons, Chapter 18 pp. 623-653. Environmental Contamination Remediation and Management series, Springer Nature. [https://doi.org/10.1007/978-3-031-34447-3_18 doi: 10.1007/978-3-031-34447-3_18]&nbsp; [[Media: MunhollandEtAl2024.pdf | Open Access Chapter]]</ref>.  
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[[File:ConderFig1.png|thumb|500px|Figure 1. Simplified Conceptual Site Model for Sites Impacted by AFFF or other PFAS Sources. Used with permission<ref name="ConderEtAl2021">Conder, J., Zodrow, J., Arblaster, J., Kelly, B., Gobas, F., Suski, J., Osborn, E., Frenchmeyer, M., Divine, C., Leeson, A., 2021. Strategic resources for assessing PFAS ecological risks at AFFF sites. Integrated Environmental Assessment and Management, 17(4), pp. 746-752. [https://doi.org/10.1002/ieam.4405 doi: 10.1002/ieam.4405]</ref>]]
 
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This article provides a brief overview of the environmental toxicology and risk assessment of per- and polyfluoroalkyl substances (PFAS). The article’s main focus is on the environmental toxicology and risk assessment of PFAS derived from aqueous film-forming foam (AFFF).  
 
  
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The use of AFFF can release PFAS into the environment during fire training, an emergency response, or as a result of leaks or spills from AFFF systems. Following AFFF releases, perfluoroalkyl acids (PFAAs), particularly PFOS, PFOA, and PFHxS, tend to be the most commonly detected PFAS in environmental media. Due to their solubility, sorption, and bioaccumulation properties, perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) can be prevalent in a variety of environmental media, including groundwater, surface water, soil, sediment, biosolids, landfill leachate, plants, fish, invertebrates, and wildlife<ref>Lau, C., 2012. Perfluorinated Compounds. In: ''Molecular, Clinical and Environmental Toxicology, Volume 3: Environmental Toxicology'', A. Luch (Ed.), pp. 47-86. Springer Science and Business Media. [https://doi.org/10.1007/978-3-7643-8340-4_3 doi: 10.1007/978-3-7643-8340-4_3]</ref>.
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*A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers. Ornelles, Falta, and Divine, 2023<ref name="Ornelles">Ornelles, A.D., Falta, R.W., Divine, C.E., 2023. A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers. Ground Water, 61(2), pp. 245-254. [https://doi.org/10.1111/gwat.13265 doi: 10.1111/gwat.13265]&nbsp; [https://ngwa.onlinelibrary.wiley.com/doi/epdf/10.1111/gwat.13265 Free download from NGWA]</ref>.  
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PFAS exhibit a range of physical and chemical properties, with the fate of the PFAAs, particularly the PFCAs and PFSAs, being the most studied PFAS. PFAAs are relatively water-soluble and mobile in the environment, are not volatile (i.e., they do not evaporate to the atmosphere readily<ref>Field, J., Higgins, C., Deeb, R., Conder, J., 2017.  FAQs Regarding PFASs Associated with AFFF Use at U.S. Military Sites. Environmental Security Technology Certification Program (ESTCP) Project ER-201574. [https://serdp-estcp.mil/resources/details/ccf87a8d-f8b2-4fce-bc4a-78c32091f896 Project Website]&nbsp; [[Media: FAQ_ER-201574.pdf | Report.pdf]]</ref>) and can sorb to the organic carbon present in soil or sediment. PFAAs are more soluble and mobile compared to other persistent organic chemicals of concern documented at contaminated sites. PFAS can bioaccumulate in animals and plants, and persistent PFAS, such as PFCAs and PFSAs, do not undergo significant biodegradation or biotransformation once present in a biological system<ref>Conder, J.M., Hoke, R.A., de Wolf, W., Russell, M.H., Buck, R.C., 2008. Are PFCAs Bioaccumulative? A Critical Review and Comparison with Regulatory Criteria and Persistent Lipophilic Compounds. Environmental Science and Technology, 42(4), pp. 995-1003. [https://doi.org/10.1021/es070895g doi: 10.1021/es070895g]</ref>.  
 
  
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The current state of the science and understanding of PFAS fate and transport indicates that the human health issues associated with PFAS AFFF sites are primarily the exposure pathways associated with drinking water ingestion and dietary intake of PFAS<ref name="ZodrowEtAl2021"/>. Incidental soil ingestion and/or dust inhalation are typically of moderate concern and are recommended for inclusion into human health risk assessments, but compared to drinking water and dietary ingestion, generally result in lower exposures for most receptors. Exposures via dermal contact with soils and water, and inhalation of vapors (due to volatilization of PFAS), are generally of even lower concern for most sites with AFFF PFAS sources. Human health conceptual site models (CSMs) for AFFF sites typically reflect common receptors including current or future residents and industrial or commercial workers, depending on the current and reasonable anticipated future land uses at the site, along with potential exposures in offsite areas. Receptors associated with recreation and fishing activities may be incorporated if water resources used for recreational purposes are located near the site. Additional considerations may need to be incorporated into the CSM, such as the source of PFAS release into the environment. Release mechanism can differ based on site uses of PFAS. For example, while AFFF use often resulted in historic releases to ground surfaces, industrial emissions can result in aerial deposition, and biosolids application can  result in widespread releases to soils which result in different exposure pathways that should be considered.    
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*Low-Temperature Thermal Remediation: Gaining Traction as a Green Remedial Alternative. Horst, ''et al.'', 2018<ref name="HorstEtAl2018">Horst, J., Flanders, C., Klemmer, M., Randhawa, D.S., Rosso, D., 2018. Low-Temperature Thermal Remediation: Gaining Traction as a Green Remedial Alternative. Groundwater Monitoring and Remediation, 38(3), pp. 18-27. [https://doi.org/10.1111/gwmr.12295 doi: 10.1111/gwmr.12295]</ref>.
  
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Ecological CSMs generally focus on exposures in areas adjacent to or downgradient of initial AFFF releases which have habitats present which support ecological resources (Figure 1). Most areas at the point of AFFF releases (and many industrial areas where PFAS products are or were used) do not generally feature favorable ecological habitats that make these areas relevant for ecological risk assessment. However, the relatively high solubility of PFAS in water results in a high potential for offsite transport via groundwater, surface water and stormwater, or by erosion of impacted soils and sediment<ref name="ConderEtAl2021"/>.
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==Introduction==
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[[File: MunhollandFig1.png | thumb | 500 px | Figure 1: Components and layout of a TISR<sup>®</sup> system]]
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==Toxicological Effects of PFAS==
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TISR<sup>®</sup> utilizes [[Wikipedia: Downhole heat exchanger | borehole heat exchangers (BHEs)]] to heat target treatment areas in the subsurface. This is achieved through a combination of solar collectors, which harness solar radiation as heat, and the utilization of other heat sources such as waste heat or hybrid heating with heat pumps. That heat is then transferred to the subsurface via a closed loop circulation system connected to the BHEs (Figure 1). By incorporating these additional heat sources, TISR<sup>®</sup> ensures a more robust and constant heat supply, enabling customization of the system to address specific site challenges and facilitate efficient heat transfer.
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The characterization of toxicological effects in human health risk assessments is based on toxicological studies of mammalian exposures to per- and polyfluoroalkyl substances (PFAS), primarily studies involving perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The most sensitive noncancer adverse effects involve the liver and kidney, immune system, and various developmental and reproductive endpoints<ref name="USEPA2024b">United States Environmental Protection Agency (USEPA), 2024. Per- and Polyfluoroalkyl Substances (PFAS) Final PFAS National Primary Drinking Water Regulation. [https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas Website]</ref> Agency for Toxic Substances and Disease Registry (ATSDR) 2021).  
 
  
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The heating of the subsurface through TISR<sup>®</sup> accelerates various processes such as biodegradation, abiotic reactions, and contaminant desorption and dissolution. The technology is also suitable for diverse hydrogeologic environments, including sites with low permeability zones, due to the relatively uniform thermal conductivity of geologic materials, which is unaffected by grain size<ref name="MunhollandEtAl2024"/>. This versatility allows TISR<sup>®</sup> to integrate with conventional remediation technologies, enhancing their performance.
  
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One of the key advantages of TISR<sup>®</sup> is its ability to accelerate treatment processes while minimizing energy consumption. By harnessing renewable and sustainable energy sources such as solar radiation and effectively utilizing waste heat or hybrid heating with heat pumps, TISR<sup>®</sup> delivers an efficient, cost-effective remediation solution. Compatibility with multiple conventional remediation technologies makes it an effective option for addressing a variety of contamination challenges.
  
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==Scientific Principles==
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[[File: MunhollandFig2.png | thumb | 500 px | Figure 2: Effect of temperature on hydrolysis rates for VOCs]]
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During the TISR<sup>®</sup> heating process, thermal conduction and advection play a crucial role in boosting physical, biological, and chemical processes within the treatment zones, leading to enhanced attenuation, degradation, and removal of contaminants from the subsurface<ref>Dettmer, K., 2002. A Discussion of the Effects of Thermal Remediation Treatments on Microbial Degradation Processes. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, Technology Innovation Office, Washington, DC. [[Media: dettmer2002.pdf | free report]]&nbsp; [https://www.clu-in.org/download/techdrct/dettmer.pdf free download from clu-in.org]</ref><ref name="HorstEtAl2018"/>. TISR<sup>®</sup> systems are typically designed to enhance the biological activity and performance of other active technologies, such as [[Wikipedia: Air sparging | air sparge]]/[[Soil Vapor Extraction (SVE) | soil vapor extraction]] (AS/SVE) or [[Chemical Oxidation (In Situ - ISCO) | chemical oxidation]], by increasing the subsurface temperature by approximately 10°C to 20°C. The target groundwater temperature is often set to reach up to about 35°C, which is the optimal temperature for promoting the activity of mesophilic microbial communities responsible for biodegradation of certain contaminants. In cases where the objective is to maximize abiotic hydrolysis mechanisms, such as for some chlorinated alkanes, TISR<sup>®</sup> systems can be designed to reach a final groundwater temperature of up to 60°C.
  
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[[File:RichardsonFig3.png|thumb|470px|Figure 3. Rejection of nine PFAAs by four available membrane products at the pilot-scale. Rejection data shown above was generated from permeate samples collected at 97% recovery.]]
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The effectiveness of TISR<sup>®</sup> in enhancing treatment performance has been demonstrated through several mechanisms, which are discussed below:
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[[File:RichardsonFig4.png|thumb|600px|Figure 4. Mobile high-pressure membrane treatment trailer (left) and pilot-scale closed-circuit membrane filtration system (right).]]
 
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The effectiveness of RO and NF membranes for dissolved solute rejection has led to high-pressure membranes being regarded as one of the best available technologies for PFAS removal for over a decade<ref name="ApplemanEtAl2013"/><ref name="Steinle-DarlingReinhard2008"/>. Several studies have evaluated aspects of PFAS removal by NF and RO membranes including evaluating different membrane products, the impact of operating conditions and water quality, and the influence of physicochemical characteristics of PFAS<ref name="ApplemanEtAl2013"/><ref name="SafulkoEtAl2023"/><ref name="LiuStrathmannBellona2021">Liu, C.J., Strathmann, T.J., Bellona, C., 2021. Rejection of per- and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam by high-pressure membranes. Water Research, 188, Article 116546. [https://doi.org/10.1016/j.watres.2020.116546 doi: 10.1016/j.watres.2020.116546]</ref><ref name="WangEtAl2018">Wang, J., Wang, L., Xu, C., Zhi, R., Miao, R., Liang, T., Yue, X., Lv, Y., Liu, T., 2018. Perfluorooctane sulfonate and perfluorobutane sulfonate removal from water by nanofiltration membrane: The roles of solute concentration, ionic strength, and macromolecular organic foulants. Chemical Engineering Journal, 332, p. 787-797.  [https://doi.org/10.1016/j.cej.2017.09.061 doi: 10.1016/j.cej.2017.09.061]</ref><ref name="ZhaoEtAl2016">Zhao, C., Tang, C.Y., Li, P., Adrian, P., Hu, G., 2016. Perfluorooctane sulfonate removal by nanofiltration membrane—the effect and interaction of magnesium ion / humic acid. Journal of Membrane Science, 503, p. 31-41. [https://doi.org/10.1016/j.memsci.2015.12.049 doi: 10.1016/j.memsci.2015.12.049]</ref><ref name="ZhaoEtAl2013">Zhao, C., Zhang, J., He, G., Wang, T., Hou, D., Luan, Z., 2013. Perfluorooctane sulfonate removal by nanofiltration membrane the role of calcium ions. Chemical Engineering Journal, 233, p. 224-232. [https://doi.org/10.1016/j.cej.2013.08.027 doi: 10.1016/j.cej.2013.08.027]</ref><ref name="Steinle-DarlingEtAl2010">Steinle-Darling, E., Litwiller, E., Reinhard, M., 2010. Effects of Sorption on the Rejection of Trace Organic Contaminants During Nanofiltration. Environmental Science and Technology, 44(7), p. 2592-2598. [https://doi.org/10.1021/es902846m doi: 10.1021/es902846m]</ref>. Most studies have focused on anionic (at neutral pH) [[Perfluoroalkyl_and_Polyfluoroalkyl_Substances_(PFAS)#Nomenclature | perfluoroalkyl acid (PFAA)]] rejection and reported greater than 90% separation of PFAAs by available NF and RO membranes due to electrostatic and steric exclusion from the membrane polymer<ref name="ApplemanEtAl2013"/><ref name="Steinle-DarlingReinhard2008"/><ref name="LiuStrathmannBellona2021"/>. Water quality constituents such as organic matter and cations including calcium and magnesium have been shown to reduce rejection of PFAS<ref name="LiuStrathmannBellona2021"/>. However, little is known about how fouling and membrane aging impact rejection of PFAS by NF and RO membranes and additional data are needed. A recent Department of Defense [https://serdp-estcp.mil/ ESTCP] pilot scale project ([https://serdp-estcp.mil/projects/details/0aa2fb20-b851-4b5b-ac64-e72795986b8a ER20-5369]) conducted at Colorado School of Mines (Mines) systematically evaluated the rejection of nine PFAAs by four available NF and RO products using full scale spiral-wound membrane elements in a high recovery membrane system which achieved up to 97% recovery<ref name="SafulkoEtAl2023"/>. Tight NF and the two RO membranes evaluated exhibited greater than 98% rejection of all PFAAs evaluated even at high recovery conditions (Figure 3). The loose NF membrane product evaluated provided lower than expected (based on literature) rejection of investigated PFAAs particularly at higher recovery values. These findings indicate that tight NF and RO membranes can be effective at separating PFAAs from contaminated source waters regardless of PFAA chain length. Energy requirements modeled from these experiments varied from 0.14 kWh/m<sup>3</sup> for loose NF to 0.57 kWh/m<sup>3</sup> for seawater RO<ref name="SafulkoEtAl2023"/>.
 
  
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Mines researchers have developed a mobile high-recovery closed-circuit membrane filtration system (Figure 4) that has been successfully deployed for treating groundwater at a fire training area of Wright-Patterson Air Force Base ([https://serdp-estcp.mil/projects/details/be0417c9-aaa4-4fd6-9007-7de0cdbffb85 ESTCP ER21-5136]), groundwater at Peterson Space Force Base (AFCEC BAA-031), and firetruck rinsate at Tyndall Air Force Base ([https://serdp-estcp.mil/projects/details/0aa2fb20-b851-4b5b-ac64-e72795986b8a ESTCP ER20-5369]) during recent ESTCP and AFCEC funded research projects. In these projects, NF or RO was implemented to produce a permeate stream containing low concentrations of PFAS and to concentrate PFAS into smaller volumes of retentate for subsequent destructive PFAS treatment. While NF and RO membranes have demonstrated effective rejection of PFAS, PFAS are subsequently concentrated in the membrane concentrate, or retentate stream. This concentrate stream is increasingly paired with PFAS destruction technologies, as PFAS destruction is often considered viable only for concentrated solutions of PFAS. Ongoing ESTCP funded projects include using high-recovery NF and RO to treat and concentrate groundwater leading to PFAS destruction using [[PFAS Treatment by Electrical Discharge Plasma | plasma based treatment]]<ref name="Richardson2021"> Richardson, S., 2021. Nanofiltration Followed by Electrical Discharge Plasma for Destruction of PFAS and Co-occurring Chemicals in Groundwater: A Treatment Train Approach. [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)], [https://serdp-estcp.mil/projects/details/be0417c9-aaa4-4fd6-9007-7de0cdbffb85/er21-5136-project-overview Project ER21-5136]</ref> or [[Hydrothermal Alkaline Treatment (HALT) | hydrothermal alkaline treatment (HALT)]]<ref name="Bellona2023">Bellona, C., 2023. Cradle to Grave PFAS Treatment Using Membrane and Foam Fractionation Concentration Followed by Hydrothermal Alkaline Treatment. [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)], [https://serdp-estcp.mil/projects/details/5cf08cdb-b86a-45d2-98d3-f747ba97d293 Project ER23-8367]</ref>.
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*Primary dechlorinating bacteria, such as [[Wikipedia: Dehalococcoides | Dehalococcoides]] and [[Wikipedia: Dehalogenimonas | Dehalogenimonas]], are known to be [[Wikipedia: Mesophile | mesophilic]]. Therefore, increasing the temperature can significantly enhance microbial activity and biodegradation by multiple orders of magnitude<ref>Macbeth, T., Truex, M., Powell, T., Michalsen, M., 2012. Combining Low-Energy Electrical Resistance Heating with Biotic and Abiotic Reactions for Treatment of Chlorinated Solvent DNAPL Source Areas. [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)] [https://serdp-estcp.mil/projects/details/877a3b41-6bed-4f4a-b43a-87fbcd9b7f0b/er-200719-project-overview Project ER-200719 webpage]&nbsp; [[Media: Macbeth2012_ER-200719-FR.pdf | free download]]&nbsp; [https://www.youtube.com/watch?v=-EbwKbs8scE Project Summary Presentation]</ref>.
  
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==Advantages and Limitations of the Technology for PFAS Removal==
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*Reduced iron minerals, particularly iron sulfides, can participate in the abiotic degradation of chlorinated ethenes and other contaminants. The rates of these reactions generally depend on temperature, following the [[Wikipedia: Arrhenius equation | Arrhenius equation]].
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<u>Advantages:</u>
 
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*Robust, high throughput treatment
 
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*Mature technology with well documented solute separation performance
 
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*High rejection of PFAS and other contaminants
 
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*Removes solutes at the molecular scale
 
  
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<u>Limitations:</u>
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*[[Wikipedia: Hydrolysis | Hydrolysis]] rates for certain compounds exhibit high temperature dependence. For example, a 10°C increase can lead to a 50% reduction in the half-life of [[Wikipedia: 1,1,1-Trichloroethane | 1,1,1-trichloroethane (1,1,1-TCA)]]<ref>Suthersan, S., Horst, J., Klemmer, M., Malone, D., 2012. Temperature-Activated Auto-Decomposition Reactions: An Under-Utilized In Situ Remediation Solution. Groundwater Monitoring and Remediation, 32(3), pp. 34-40. [https://doi.org/10.1111/j.1745-6592.2012.01407.x doi: 10.1111/j.1745-6592.2012.01407.x]</ref>. Figure 2 presents the calculated temperature-dependent hydrolysis rates for 13 common [[Wikipedia: Volatile organic compound | volatile organic compounds (VOCs)]] at a pH of 7.
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*Complex and often expensive pretreatment requirements for certain waters
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*Energy intensive
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*[[Wikipedia: Henry's law | Henry's Law]] constant, [[Wikipedia: Vapor pressure | vapor pressure]], solubility, and viscosity values are also temperature dependent. For instance, the Henry's Law constant values for many VOCs, including [[Wikipedia: Tetrachloroethylene | tetrachloroethene (PCE)]], have been observed to double between 8 and 24°C<ref>Chen, F., Freedman, D.L., Falta, R.W., Murdoch, L.C., 2012. Henry's law constants of chlorinated solvents at elevated temperatures. Chemosphere, 86(2), pp.156-165. [https://doi.org/10.1016/j.chemosphere.2011.10.004 doi: 10.1016/j.chemosphere.2011.10.004]</ref>.
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*High capital costs
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*Membrane fouling requiring high chemical usage for cleaning
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*Rates of other processes that often limit the pace of remediation, such as dissolution, desorption, and [[Matrix Diffusion | back diffusion]], are positively correlated with temperature. This results in an enhanced bioavailability of contaminant mass that may otherwise be inaccessible.
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*Concentrated waste stream requiring disposal or destruction
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*Permeate quality depends on feed water concentration
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These various mechanisms collectively contribute to the improved performance of other active treatments when temperature is moderately increased by utilization of TISR®.
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*Greater operation complexity than most water treatment processes
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*Water loss due to membrane separation
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==Implementation and Practical Considerations==
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[[File: MunhollandFig3.png | thumb | 500 px | Figure 3: Transformation of 1,1-DCE and VC following installation of a TISR<sup>®</sup> system]]
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TISR<sup>®</sup> has proven successful in reducing contaminant concentrations across diverse hydrogeologic settings, including those with low and complex hydraulic conductivity conditions. Figure 3 shows a sharp initial decrease in [[Wikipedia: 1,1-Dichloroethylene | 1,1-dichloroethene (1,1-DCE)]] concentrations due to enhanced biodegradation, and then a temporary small increase followed by subsequent decreases in 1,1-DCE concentrations to below detection limits, possibly the result of temperature-enhanced desorption or dissolution of 1,1-DCE from the aquifer. There is also a temporary increase and then decrease in the concentrations of [[Wikipedia: Vinyl chloride | vinyl chloride (VC)]] (a biodegradation product) to very low levels.
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The TISR<sup>®</sup> system construction utilizes off-the-shelf modular components, promoting cost-efficiency, reusability, and a reduced carbon footprint. Waste heat can supplement or replace the solar setup, and remote monitoring through dashboard apps reduces operation and maintenance costs. TISR® projects typically achieve an average capital cost payback within 1 to 3 years due to accelerated rates of remediation.
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When implementing TISR<sup>®</sup>, [[Wikipedia: Solar irradiance | solar insolation]] and groundwater velocity must be considered for optimal equipment sizing and cycling. Depending on remedial goals and site history and conditions, the TISR<sup>®</sup> system and target temperatures may be designed to enhance specific remedial mechanisms (e.g. hydrolysis over bioremediation). Recently Ornelles ''et al.''<ref name="Ornelles"/> developed an easy to use Excel-based model that can be used to optimize TISR<sup>®</sup> design and predict subsurface temperature changes over time. Frequent monitoring of the temperature and microbial community composition relative to targets is useful for evaluating treatment effectiveness and optimizing system performance. The system and target temperatures can be customized to enhance specific remedial mechanisms based on site conditions and goals.
  
 
==Summary==
 
==Summary==
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High-pressure membranes including NF and RO are well established technologies used in a variety of water treatment fields for the purification of water resources and industrial process waste streams. Research conducted over the past decade has demonstrated that various available membrane products can achieve high rejection of PFAS, enabling compliance with state and federal PFAS regulations. As opposed to adsorbent based PFAS removal technologies (e.g., [[PFAS Ex Situ Water Treatment#Activated Carbon Adsorption | activated carbon]], [[PFAS Treatment by Anion Exchange | ion exchange]]), high-pressure membranes do not have a finite capacity for PFAS removal and do not exhibit breakthrough. High-recovery membrane systems are being implemented into ex situ treatment trains to simultaneously treat PFAS impacted water resources and concentrate PFAS into the retentate stream to enable more effective and efficient PFAS destruction.
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TISR<sup>®</sup> is a cost-effective and adaptable technology that can be customized to address specific site challenges. It can be used as a standalone solution or be integrated with existing remediation strategies to enhance their effectiveness. TISR<sup>®</sup> is particularly effective in challenging hydrogeological conditions and can be optimized to suit specific treatment mechanisms. By shortening the active remediation timeframe, TISR<sup>®</sup> reduces lifecycle costs and minimizes the carbon footprint associated with the remediation process.
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<br clear="right"/>
  
 
==References==
 
==References==
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==See Also==
 
==See Also==
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[https://vimeo.com/1019489395 TISR<sup>®</sup> Explanation Video]

Latest revision as of 19:44, 13 October 2026

Thermal In Situ Sustainable Remediation to Enhance Biotic and Abiotic Reactions and Accelerate Remediation Timeframes

Thermal In Situ Sustainable Remediation (TISR®; US Pat. Nos. 10,384,246 and 10,688,545) is a cost-effective and adaptable low temperature thermal remediation technology that accelerates contaminant treatment. It achieves this by enhancing biotic and abiotic contaminant degradation rates through a modest increase in subsurface temperature. TISR® is suitable for a wide range of hydrogeologic settings. It also offers reduced operational costs, a lower carbon footprint, and possibly shorter remedial timeframes than more conventional methods.

Related Article(s):

Contributors: Jonah Munholland, Julia Vidonish, and Craig Divine

Key Resources:

  • Thermal In Situ Sustainable Remediation to Enhance Biotic and Abiotic Reactions and Accelerate Remediation Timeframes, Final Report. ESTCP Project ER20-5028[1].
  • Advances in Low-Temperature Thermal Remediation. Munholland et al., 2024[2].
  • A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers. Ornelles, Falta, and Divine, 2023[3].
  • Low-Temperature Thermal Remediation: Gaining Traction as a Green Remedial Alternative. Horst, et al., 2018[4].

Introduction

File:MunhollandFig1.png
Figure 1: Components and layout of a TISR® system

TISR® utilizes borehole heat exchangers (BHEs) to heat target treatment areas in the subsurface. This is achieved through a combination of solar collectors, which harness solar radiation as heat, and the utilization of other heat sources such as waste heat or hybrid heating with heat pumps. That heat is then transferred to the subsurface via a closed loop circulation system connected to the BHEs (Figure 1). By incorporating these additional heat sources, TISR® ensures a more robust and constant heat supply, enabling customization of the system to address specific site challenges and facilitate efficient heat transfer.

The heating of the subsurface through TISR® accelerates various processes such as biodegradation, abiotic reactions, and contaminant desorption and dissolution. The technology is also suitable for diverse hydrogeologic environments, including sites with low permeability zones, due to the relatively uniform thermal conductivity of geologic materials, which is unaffected by grain size[2]. This versatility allows TISR® to integrate with conventional remediation technologies, enhancing their performance.

One of the key advantages of TISR® is its ability to accelerate treatment processes while minimizing energy consumption. By harnessing renewable and sustainable energy sources such as solar radiation and effectively utilizing waste heat or hybrid heating with heat pumps, TISR® delivers an efficient, cost-effective remediation solution. Compatibility with multiple conventional remediation technologies makes it an effective option for addressing a variety of contamination challenges.

Scientific Principles

File:MunhollandFig2.png
Figure 2: Effect of temperature on hydrolysis rates for VOCs

During the TISR® heating process, thermal conduction and advection play a crucial role in boosting physical, biological, and chemical processes within the treatment zones, leading to enhanced attenuation, degradation, and removal of contaminants from the subsurface[5][4]. TISR® systems are typically designed to enhance the biological activity and performance of other active technologies, such as air sparge/ soil vapor extraction (AS/SVE) or chemical oxidation, by increasing the subsurface temperature by approximately 10°C to 20°C. The target groundwater temperature is often set to reach up to about 35°C, which is the optimal temperature for promoting the activity of mesophilic microbial communities responsible for biodegradation of certain contaminants. In cases where the objective is to maximize abiotic hydrolysis mechanisms, such as for some chlorinated alkanes, TISR® systems can be designed to reach a final groundwater temperature of up to 60°C.

The effectiveness of TISR® in enhancing treatment performance has been demonstrated through several mechanisms, which are discussed below:

  • Primary dechlorinating bacteria, such as Dehalococcoides and Dehalogenimonas, are known to be mesophilic. Therefore, increasing the temperature can significantly enhance microbial activity and biodegradation by multiple orders of magnitude[6].
  • Reduced iron minerals, particularly iron sulfides, can participate in the abiotic degradation of chlorinated ethenes and other contaminants. The rates of these reactions generally depend on temperature, following the Arrhenius equation.
  • Rates of other processes that often limit the pace of remediation, such as dissolution, desorption, and back diffusion, are positively correlated with temperature. This results in an enhanced bioavailability of contaminant mass that may otherwise be inaccessible.

These various mechanisms collectively contribute to the improved performance of other active treatments when temperature is moderately increased by utilization of TISR®.

Implementation and Practical Considerations

File:MunhollandFig3.png
Figure 3: Transformation of 1,1-DCE and VC following installation of a TISR® system

TISR® has proven successful in reducing contaminant concentrations across diverse hydrogeologic settings, including those with low and complex hydraulic conductivity conditions. Figure 3 shows a sharp initial decrease in 1,1-dichloroethene (1,1-DCE) concentrations due to enhanced biodegradation, and then a temporary small increase followed by subsequent decreases in 1,1-DCE concentrations to below detection limits, possibly the result of temperature-enhanced desorption or dissolution of 1,1-DCE from the aquifer. There is also a temporary increase and then decrease in the concentrations of vinyl chloride (VC) (a biodegradation product) to very low levels.

The TISR® system construction utilizes off-the-shelf modular components, promoting cost-efficiency, reusability, and a reduced carbon footprint. Waste heat can supplement or replace the solar setup, and remote monitoring through dashboard apps reduces operation and maintenance costs. TISR® projects typically achieve an average capital cost payback within 1 to 3 years due to accelerated rates of remediation.

When implementing TISR®, solar insolation and groundwater velocity must be considered for optimal equipment sizing and cycling. Depending on remedial goals and site history and conditions, the TISR® system and target temperatures may be designed to enhance specific remedial mechanisms (e.g. hydrolysis over bioremediation). Recently Ornelles et al.[3] developed an easy to use Excel-based model that can be used to optimize TISR® design and predict subsurface temperature changes over time. Frequent monitoring of the temperature and microbial community composition relative to targets is useful for evaluating treatment effectiveness and optimizing system performance. The system and target temperatures can be customized to enhance specific remedial mechanisms based on site conditions and goals.

Summary

TISR® is a cost-effective and adaptable technology that can be customized to address specific site challenges. It can be used as a standalone solution or be integrated with existing remediation strategies to enhance their effectiveness. TISR® is particularly effective in challenging hydrogeological conditions and can be optimized to suit specific treatment mechanisms. By shortening the active remediation timeframe, TISR® reduces lifecycle costs and minimizes the carbon footprint associated with the remediation process.

References

  1. ^ Divine, C., Munholland, J., Zardouzian, E., Justicia-Leon, S., Aspinall, J.V., Randhawa, D., Falta, R., Freedman, D., Becker, M., 2025. Thermal In Situ Sustainable Remediation to Enhance Biotic and Abiotic Reactions and Accelerate Remediation Timeframes, Final Report. Environmental Security Technology Certification Program (ESTCP), Project ER20-5028. Project Website  Final Report.pdf
  2. ^ 2.0 2.1 Munholland, J, Rosso, D., Randhawa, D., Devine, C., Pennington, A., 2024. Advances in Low-Temperature Thermal Remediation. In: García-Rincón, J., Gatsios, E., Lenhard, R.J., Atekwana, E.A., Naidu, R. (eds), Advances in the Characterisation and Remediation of Sites Contaminated with Petroleum Hydrocarbons, Chapter 18 pp. 623-653. Environmental Contamination Remediation and Management series, Springer Nature. doi: 10.1007/978-3-031-34447-3_18  Open Access Chapter
  3. ^ 3.0 3.1 Ornelles, A.D., Falta, R.W., Divine, C.E., 2023. A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers. Ground Water, 61(2), pp. 245-254. doi: 10.1111/gwat.13265  Free download from NGWA
  4. ^ 4.0 4.1 Horst, J., Flanders, C., Klemmer, M., Randhawa, D.S., Rosso, D., 2018. Low-Temperature Thermal Remediation: Gaining Traction as a Green Remedial Alternative. Groundwater Monitoring and Remediation, 38(3), pp. 18-27. doi: 10.1111/gwmr.12295
  5. ^ Dettmer, K., 2002. A Discussion of the Effects of Thermal Remediation Treatments on Microbial Degradation Processes. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, Technology Innovation Office, Washington, DC. free report  free download from clu-in.org
  6. ^ Macbeth, T., Truex, M., Powell, T., Michalsen, M., 2012. Combining Low-Energy Electrical Resistance Heating with Biotic and Abiotic Reactions for Treatment of Chlorinated Solvent DNAPL Source Areas. Environmental Security Technology Certification Program (ESTCP) Project ER-200719 webpage  free download  Project Summary Presentation
  7. ^ Suthersan, S., Horst, J., Klemmer, M., Malone, D., 2012. Temperature-Activated Auto-Decomposition Reactions: An Under-Utilized In Situ Remediation Solution. Groundwater Monitoring and Remediation, 32(3), pp. 34-40. doi: 10.1111/j.1745-6592.2012.01407.x
  8. ^ Chen, F., Freedman, D.L., Falta, R.W., Murdoch, L.C., 2012. Henry's law constants of chlorinated solvents at elevated temperatures. Chemosphere, 86(2), pp.156-165. doi: 10.1016/j.chemosphere.2011.10.004

See Also

TISR® Explanation Video

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