Balancing sustainability goals and treatment efficacy for PFAS removal from water

Introduction

Poly- and perfluoroalkyl substances (PFAS) constitute a group of persistent organic pollutants characterized by the exceptionally strong carbon-fluorine bonds, which are resistant to degradation under environmental conditions^1,2,3,4,5. These substances exhibit remarkable resistance to environmental degradation due to their robust chemical structure, which renders them resistant to heat, alkali, and acid. Additionally, their persistence is reinforced by the lack of evolutionary pressure for microbial degradation⁶. Consequently, PFAS have found widespread use in various industrial applications, including non-stick cookware⁷, food packaging^2,8,9, aqueous film-forming foam⁹, plastics¹⁰, and semiconductor manufacturing^11,12. Since the 1940s⁷, the discharge of PFAS from commercial and industrial sources has led to their widespread presence in water sources worldwide, with concentrations ranging from ng/L to sometimes μg/L levels^2,4. PFAS contamination has been detected in various water sources, including drinking water, groundwater, surface water, tap water, and industrial effluents, prompting the establishment of environmental quality standards, and guidelines in many countries^2,13,14,15. Recognized by regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and the European Chemicals Agency (ECHA) as emerging contaminants, some classes of PFAS, such as perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate acid (PFOS), pose significant health and environmental risks due to their carcinogenic properties^{16,17,18,19,20,21}. However, the environmental persistence and bioaccumulative nature of all PFAS make them worrisome for future generations, as these chemicals do not readily degrade and can accumulate in the environment over time. To address this global challenge, numerous organizations have taken regulatory measures. For instance, the Stockholm Convention designated PFOS and PFOA as persistent organic pollutants in 2009, and 2019, respectively^22,23. The European Commission has outlined its chemicals strategy, which includes plans to phase out non-essential uses of PFAS within the EU^24,25. The International Chemicals Management has identified PFAS as a priority issue. In 2016, the U.S. EPA established a drinking water health advisory level of 70 ng/L for the combined concentrations of PFOA and PFOS²⁶. The U.S. EPA recently established the first national drinking water standard for six PFAS compounds, setting maximum contaminant levels at 4.0 parts per trillion for PFOA and PFOS, and 10.0 parts per trillion for perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA). PFAS mixtures containing two or more of PFHxS, PFNA, HFPO-DA, and perfluorobutane sulfonic acid (PFBS) will be regulated using a Hazard Index of 1. This rule will require mandatory monitoring by 2027, with compliance by 2029²⁷. On October 7, 2024, the U.S. EPA issued new aquatic life water quality criteria for PFOA and PFOS, with freshwater acute limits up to 42 times lower than 2022 drafts²⁸. Additionally, the U.S. EPA set acute saltwater aquatic life benchmarks for PFOS (7 mg/L), and PFOA (0.55 mg/L) and aquatic life benchmarks for eight additional PFAS, PFBS, PFNA, PFHxS, perfluorohexanoic acid (PFHxA), perfluorobutanoic acid (PFBA), perfluorodecanoic acid (PFDA), hexadecafluoro-2-decenoic acid (8:2 FTUCA), pentadecafluorodecanoic acid (7:3 FTCA) in freshwater²⁹. Following these guidelines, the North Carolina Department of Environmental Quality released interim maximum concentrations for eight PFAS (e.g., PFOA, PFOS, PFHxS, PFHxA, PFNA, PFBS, Hexafluoropropylene oxide dimer acid (GenX), and PFBA) in groundwater³⁰, and the California Office of Environmental Health Hazard Assessment set a notification level for PFHxA in drinking water at 1 µg/L³¹. On October 21, 2024, the Australian National Health and Medical Research Council proposed health-based drinking water guidelines for four PFAS compounds, including PFOS and PFOA at 4 ng/L and 200 ng/L, respectively, which are 17.5 and 2.8 times lower than the current regulations³². Full details of these regulations are provided in Supplementary Tables 1–4. As a result of these regulations, researchers worldwide are actively seeking effective treatment techniques to remove PFAS from water sources.

The predominant focus of recent research lies in investigating the efficacy of various technologies for removing PFAS, encompassing adsorption, membrane filtration, destructive processes, and other methodologies. Among these, ion exchange (IX)^33,34,35,36 and granular activated carbon (GAC)^37,38,39 are the most prevalent adsorption techniques employed for PFAS removal. However, due to environmental concerns about water contamination and resource depletion, considerable attention has been directed toward the regeneration, reuse, and disposal aspects associated with IX and GAC^{40,41,42,43,44}. Nanofiltration and reverse osmosis have emerged as leading membrane technologies for PFAS removal because of their high removal efficiencies^45,46,47,48. However, their implementation is constrained to specific contexts due to the need for pretreatment measures, high operating cost, and energy demand^49,50. Beyond these conventional approaches, a range of alternative technologies such as oxidation⁵¹, activated persulfate oxidation⁵², electrochemical advanced oxidation process⁵³, plasma⁵⁴, and foam fractionation⁵⁵ have been explored for PFAS treatment from water sources. Groundwater and surface water are primary sources of drinking water, which is why most pilot- and lab-scale PFAS treatment studies focus on these water sources. However, addressing PFAS contamination at its sources, such as industrial discharge sites or landfill leachate, is crucial for sustainable, long-term water quality management. While PFAS regulations primarily target drinking water, it is equally important to address secondary sources of contamination, such as landfill leachate. Landfills, a common waste disposal method, generate leachate as precipitation infiltrates solid waste, creating a liquid that may contain hazardous contaminants, including PFAS^54,56. This leachate often reaches wastewater treatment plants, where PFAS may not be fully removed, potentially contaminating surface water and groundwater used for drinking. Therefore, managing PFAS holistically, including groundwater, surface water, and landfill leachate, is crucial for ensuring water quality and safety. Driven by the urgency to address environmental PFAS contamination, research has primarily focused on determining the efficacy of these technologies, with little attention given to assessing their sustainability.

Sustainability, encompassing economic, environmental, and social impacts, is a paramount consideration in PFAS treatment research⁵⁷. While meeting regulatory standards is important, demonstrating financial viability and social impacts are crucial for industry and community acceptance, respectively. Sustainability facilitates the selection of treatment methods based on specific needs. The assessment of environmental impacts through life cycle assessment (LCA) and financial feasibility through techno-economic analysis (TEA) or life cycle cost analysis (LCCA) serve as prominent methodologies indicating sustainability⁵⁸. Social impacts are usually assessed through social sustainability evaluation matrix⁵⁹. For PFAS, most of the existing research has focused on removal efficiencies using GAC and IX technologies, resulting in limited studies that comprehensively address their economic, environmental, and social impacts. There exists a substantial research gap regarding the sustainability of these technologies, and current literature fails to provide a comprehensive understanding of the overarching concept of sustainability for PFAS treatment. Selecting the appropriate water treatment method requires considering water types, usage, regulations, costs, and final PFAS fate which is essential for informed decision-making via LCA and TEA. However, it is not clear which technologies are the most sustainable across various contexts. Therefore, a comprehensive study is needed to consolidate the literature on sustainability of PFAS treatment for effective decision-making.

This review consolidated existing research on economic, environmental, and social impacts of removing PFAS from various water sources using different water treatment techniques. The overarching goal of this study is to clarify the current status, future directions, and necessary actions for sustainable PFAS water treatment. The two major specific objectives are (1) to understand how and to what extent previous literature has evaluated sustainability of PFAS treatment technologies and (2) to develop a potential conceptual framework for characterizing the sustainability of PFAS treatment technologies. This review consolidated literature on evaluating the sustainability of PFAS-contaminated water treatment. From a screening of 278 articles, only 10 studies were identified as relevant to the goals of this study. Information on environmental sustainability, financial viability, and social impacts was extracted and consolidated from these articles to find out the most sustainable treatment technology for different scenarios. Next, a systematic framework was developed for future researchers to guide the selection of sustainable PFAS treatment technologies. This study will provide important insights into sustainability, offering decision-makers a valuable resource for identifying the sustainable and economically viable PFAS treatment technology from water sources.

Functional unit to standardize sustainability indicators

Studying sustainability for PFAS treatment from water requires a focus on several key components, such as the functional unit, system boundary, water type, and methodological approaches. These components are essential for assessing the environmental sustainability, social impacts, and financial feasibility of various treatment technologies (Fig. 1). By standardizing sustainability indicators through these key components, researchers can develop more robust and comparable assessments, ultimately advancing the field of PFAS treatment and contributing to the broader goal of sustainable water management. Figure 1 illustrates the research focus and gaps in the current body of literature. The thickness of each line represents the number of reviewed papers, highlighting areas where research is concentrated and where further investigation is needed. This visual representation aids in identifying trends, emerging technologies, and underexplored areas, guiding future research efforts towards a more comprehensive understanding of PFAS treatment sustainability. Details on how the literature review was systematically conducted are included in the Supplementary Information Supplementary Section 1, and Supplementary Table 5 has all the information used in the development of Fig. 1.

Balancing sustainability goals and treatment efficacy for PFAS removal from water — **Fig. 1**

Functional unit and system boundary

Functional unit is a standardized measure used in various sustainability analyses to compare indicators across different technologies, systems, or processes. This measurement is crucial for comparisons on an equivalent basis, ensuring results are based on consistent performance metrics. In the context of sustainability of PFAS treatment, various functional units were identified across the literature, including the mass of PFAS^60,61 and mass of sludge⁶². However, Fig. 1 shows a predominant emphasis on the unit volume of water. Regional and global differences in domestic water consumption, influenced by climate, infrastructure, and societal factors, highlight the challenges of establishing a standardized functional unit. The majority of examined papers opted for a functional unit based on the volume of water, with 70% of the sampled literature employing 1 m³ of treated water as the standard^{61,63,64,65,66,67,68}. Notably, one paper deviated from this trend, utilizing 800,000 gallons of groundwater per day as its functional unit⁵⁸. The chosen functional unit corresponds to the actual daily water consumption of Brighton’s population, estimated at approximately 8000 people with an average daily consumption of 100 gallons per capita per day. Landfill leachate is a significant secondary source of PFAS in water, making sustainable treatment methods for PFAS removal essential. However, with only one study conducted in this area, a substantial research gap remains. The importance of selecting a functional unit is highlighted in sustainability assessments of leachate treatment. When “1 g of PFAS removed” is used as the functional unit, the assessment reveals higher environmental and human health impacts compared to using “1 m³ of leachate treated” as the functional unit⁶¹. Evaluating per mass of PFAS removed is more relevant to human and environmental health, while evaluating per volume of PFAS-impacted water treatment is more relevant to costs and engineering. This demonstrates that the choice of a functional unit significantly influences the overall sustainability outcomes of PFAS treatment technologies. However, the water treatment industry operates based on the volume of water treated, and associated costs are typically calculated per unit volume. Therefore, most of the reviewed papers have utilized water volume as the functional unit.

A system boundary in the context of sustainability assessments defines the limits of what is included and excluded in the analysis of a system, product, or process⁶⁹. It determines which stages, processes, flows, and impacts are considered within the scope of the evaluation^70,71. For PFAS treatment technologies, clearly defining these boundaries is essential to capture the comprehensive environmental, economic, and social implications associated with each technology. The persistent nature of PFAS necessitates a thorough consideration of the fate of these substances across different treatment methods, yet current literature often overlooks this aspect. Most of the existing studies have defined their system boundaries around the removal of PFAS, with limited attention given to the ultimate destruction of these compounds (e.g., incineration^63,64,66). This omission is significant, as the destruction phase can entail considerable environmental, economic, and social costs that are not accounted for in current assessments. To comprehensively evaluate the sustainability impacts of PFAS treatment technologies, future research should expand system boundaries to include destruction technologies, such as advanced oxidation processes⁷², electrochemical oxidation^72,73, plasma⁷³, activated persulfate oxidation^52,74,75,76, and ultrasonication^77,78. This broader perspective will provide a more holistic view of sustainability, enabling the accurate assessment of the true sustainability implications of PFAS treatment technologies.

Water type

Water type selection is significant in sustainability studies, guiding the choices of treatment technologies based on varying pollutant concentrations and characteristics of PFAS. PFAS concentrations range from 20 to 20,000 ng/L in groundwater^79,80, 11-23 ng/L in well water⁸¹, 0.4–40 ng/L in drinking water^82,83, 5.1 to 298,559 ng/L in landfill leachate⁸⁴, 3–430 ng/L in wastewater influent^{85,86,87,88,89,90,91,92}, and 6–500 ng/L in wastewater effluent^{87,88,89,91,92,93,94} systems across USA, China, Europe, and Australia^95,96; PFAS composition was primarily represented by PFOA, PFOS and PFHxS. Groundwater has been predominantly researched for PFAS treatment, driven by its prevalence, regulatory importance, ease of study, persistence, and ecological impact (Fig. 1)^{58,63,64,65,67}. Groundwater contaminated by fire extinguishing activities, particularly from military and industrial sites using aqueous film-forming foam (AFFF), poses significant challenges for PFAS treatment due to high PFAS concentrations. Fluorine-free alternatives have shown improved biodegradability and reduced environmental persistence compared to AFFF^66,97. Nonetheless, some alternatives may still present similar or higher environmental impacts^98,99. Additional research is required to fully understand the sustainability of these alternative firefighting foams. As the volume of landfilled solid waste continues to grow globally, the generation of leachate is expected to increase correspondingly¹⁰⁰. Landfill leachate contains a complex mix of contaminants, including PFAS^101,102. Its high variability in PFAS concentrations necessitates robust, and adaptable treatment technologies. Studies should emphasize the requirement for systems capable of handling this variability effectively. Meeting the stringent levels of PFOA and PFOS concentrations requires highly effective and sustainable treatment technologies, which are still not adequately covered in current literature. Understanding the specific challenges and opportunities of each water type allows for better tailoring of PFAS treatment technologies to achieve sustainability in environmental, social, and financial terms. This comprehensive approach will ensure effective mitigation of PFAS contamination across various water sources.

Indicator and impact assessment method

Assessing the sustainability of treatment technologies for PFAS removal from water sources require a multifaceted approach. In this study, we reviewed existing literature to examine how treatment technologies for PFAS are evaluated in terms of sustainability. We focused on three key indicators commonly used in these studies: environmental sustainability, social impacts, and financial viability. The reviewed studies employed various methodologies, including LCA, LCCA, and TEA to quantify these indicators. Different impact assessment methods were integrated into these evaluations to provide a comprehensive analysis of the sustainability of PFAS treatment technologies. The assessment tools included TRACI^{58,61,63,64,65,67}, ReCipe^61,62,64, environmental footprint⁶⁶, Impact 2002 + ⁶⁰, social sustainability evaluation matrix⁵⁸, and net present value^{58,61,62,64,68}. These tools have been utilized to assess any treatment technologies environmental sustainability, social impacts, and financial viability values. The selection of impact assessment methodology varies depending on the type of infrastructure and the research objectives. This choice can significantly influence the results due to key differences in how the environmental relevance of indicators is considered. In sustainability studies, particularly in LCA, impact assessment methodologies are generally classified into two main types: midpoint models and endpoint models. These models are used to evaluate the environmental impacts of a system, product, or process at different stages and levels of detail. Midpoint models provide a greater level of certainty because they focus on specific impact categories, such as carbon footprint and water footprint, before they are aggregated. In contrast, endpoint models consolidate information into a single score, making them more understandable to decision-makers by summarizing the overall damage to human health, ecosystems, and resources. Methods like TRACI, ReCiPe, and the environmental footprint can serve as either midpoint or endpoint methodologies based on their application. For example, when TRACI, ReCiPe, or environmental footprint are used to assess specific impact categories, they function as midpoint indicators. Conversely, when they are applied to evaluate comprehensive environmental damage, they align with endpoint methodologies. Integrating LCA and TEA with tools like TRACI, ReCiPe, and environmental footprint ensures a detailed analysis of environmental impacts. This integration provides a robust framework for assessing sustainability by balancing detailed environmental data with broader impact evaluations. Simultaneously, the social sustainability evaluation matrix and net present value offer valuable insights into social and financial aspects, respectively. Advanced methodologies such as dynamic^103,104 and consequential LCA^105,106 (which consider time-dependent and indirect environmental impacts), and hybrid LCA models that combine process-based LCA with input-output analysis¹⁰⁷, have been widely applied to evaluate the sustainability of treatment technologies for other pollutants but are yet to be fully explored in the context of PFAS removal. In recent days, machine learning (ML) has been applied in LCAs to estimate environmental impact factors, conduct sensitivity analyses, and develop surrogate LCAs for predicting life cycle impacts based on early design data^108,109. Machine learning also aids in data cleaning, predicting system performance, and optimizing processes, offering opportunities to improve life cycle inventories and enhance impact assessments treatment technologies^110,111. By applying these advanced methodologies to PFAS removal technologies, future studies could offer more novel insights into environmental, social, and financial trade-offs, promoting a holistic view of sustainability for PFAS treatment.

Environmental sustainability

Environmental sustainability has attracted the most attention among the three sustainability indicators (Fig. 1). In the majority of studies, TRACI and ReCiPe methodologies have been commonly employed to evaluate the environmental sustainability of GAC and IX technologies across various water types^{58,61,62,63,64,65,67}. However, environmental footprint was utilized to assess the environmental impact of GAC in fire fighting foam (i.e., AFFF) impacted water, while Impact 2002+ was employed for PFAS decomposition technology in subcritical water^60,66. LCA assesses environmental impacts using both midpoint and endpoint indicators. Ozone depletion, global warming, smog, acidification, eutrophication, carcinogenic, and non-carcinogenic effects, respiratory effects, ecotoxicity, and fossil fuel depletion are included as midpoint indicators, whereas human health, ecological quality, climate change, resources are part of the endpoint indicators. Understanding these indicators helps to evaluate the varying impacts of GAC and IX technologies.

Variations within GAC and IX technologies, such as single-use GAC adsorbents and single-use IX resins, have unique environmental implications. Methods for reactivating and regenerating these materials also introduce distinct trade-offs that affect sustainability outcomes. However, numerous studies suggest that under similar experimental conditions from an environmental sustainability standpoint, IX generally exhibits lower environmental impacts compared to GAC^{58,63,64,66,67}. Key factors behind the superior adsorption performance of IX resins compared to GAC include variations within IX resins, polymer composition (styrene vs. acrylic), pore structure (gel vs. macroporous), and functional groups (e.g., quaternary or tertiary amines)^{34,112,113,114}. These functional groups enable strong ionic interactions with PFAS molecules, while the tailored pore structure enhances contaminant contact, increasing adsorption efficiency. Such combination of chemical and physical properties gives IX resins a higher adsorption capacity and longer bed life, leading to less frequent media replacement and lesser environmental impacts from production and disposal compared to GAC. The high ozone depletion impacts from single-use IX resins are due to the release of ozone-depleting chemicals during their production. Although the regeneration process itself may have some environmental impacts, it reduces the need for continuous production of new resins, thereby lowering the overall release of ozone-depleting chemicals. By reducing the demand for new resin production, the lifecycle of regenerable resins results in fewer ozone-depleting emissions compared to single-use resins.

GAC may demonstrate higher environmental impacts compared to IX in certain scenarios, such as in the treatment of short-chain PFAS or AFFF-impacted water⁶⁴. However, it remains a viable option in specific contexts. GAC is particularly effective for cases with high initial contaminant loads, low dissolved organic carbon concentrations, and targeting longer-chained PFAS like PFOA and PFOS^45,58,67,115. Proper reactivation techniques can mitigate GAC’s negative environmental impacts. For instance, thermally reactivated GAC has been found to have lower impacts than single-use GAC and even regenerable IX treatments⁶⁴. Utilizing off-site thermal reactivation and reuse of spent GAC media significantly reduces impacts by decreasing the need for new adsorbent material, and operating at lower temperatures (e.g., 815 °C compared to 1200 °C for hazardous waste incinerators)^64,116,117. Regeneration techniques for IX resins play a key role in its environmental sustainability. Regenerable IX systems, while generally less impactful than single-use GAC, can have significant environmental impacts due to the infrastructure and chemical-intensive processes required for resin regeneration and regenerant recycling. The environmental impacts of IX resins regeneration could be reduced by recycling methanol and/or brine, thereby, decreasing the amount of waste sent to incineration. However, altering the composition of the regeneration solution requires careful consideration as replacing NaCl with alternative salts can increase environmental impacts⁶³. Another study showed that the regeneration and reuse of IX resins with electrochemical oxidation in groundwater significantly reduces global warming potential (GWP), especially when the energy efficiency of oxidation is between 192 kWh/m³ and 656 kWh/m³. Regeneration and reuse of IX resins coupling with electrochemical oxidation had the lowest GWP, reducing it by approximately 49% compared to IX following incineration⁶⁵. These findings suggest that regeneration and reuse of IX resins could be one of the most environmentally friendly options for treating PFAS-contaminated groundwater.

Several studies have focused on different water sources using various techniques for PFAS treatment. A comprehensive LCA was performed to evaluate three end-of-life options for aqueous film-forming foam containing spent fire-extinguishing waters: functional precipitation agents (PerfluorAd process), GAC, and direct incineration⁶⁶. All three scenarios ultimately result in the incineration of PFAS. The LCA results showed that the PerfluorAd process performed best across all environmental impact categories for PFAS treatment. Another study evaluated the sorption capacity of optimized sludge-based GAC media for removing nine commonly detected PFAS from simulated wastewater⁵⁵. Notably, it was found that reducing the ZnCl₂ impregnation ratio from 2.5 M to 1.5 M significantly decreased freshwater ecotoxicity, marine ecotoxicity, and human non-carcinogenic toxicity of the treated water by 49%⁶². The ZnCl₂ impregnation ratio refers to the ratio of ZnCl₂ used to the precursor material. Specifically, it indicates the amount of ZnCl₂ used in the chemical activation process of the sludge to produce activated carbon. Further techniques such as multistage membrane technology and subcritical water decomposition have also been investigated to find the environmental sustainability of these technologies. Multistage membrane technology for PFAS removal from landfill leachate found that offsite treatment was generally more sustainable than onsite treatment at high PFAS concentrations, highlighting the need for improved membrane, electricity, and chemical usage efficiencies for onsite treatment⁶¹. Exploring subcritical water decomposition of PFOS, researchers found that maintaining high temperature and pressure accounted for 99.8% of the environmental impact, suggesting that enhancing energy efficiency and catalytic effectiveness is crucial for reducing the environmental impact of subcritical water decomposition processes⁶⁰. The composition of water plays a crucial role in treatment effectiveness because different pollutants, such as natural organic matter (NOM) or inorganic ions, influence the efficiency and lifespan of treatment systems, leading to increased resource use. Water quality varies widely across different contexts, with some sources containing higher concentrations of organic contaminants, while others have elevated levels of inorganic ions. These contextual differences in water quality mean that treatment media may become exhausted more quickly in areas with complex or heavily polluted water compositions, requiring more frequent regeneration or replacement. This increased maintenance contributes to higher resource consumption, energy use, and waste generation. As a result, the environmental footprint of the treatment method is accelerated, underscoring the importance of considering local water composition in environmental impact assessments to accurately evaluate the system’s sustainability. These findings collectively highlight the environmental trade-offs between various PFAS treatment technologies. The choice of treatment should consider the specific PFAS contamination scenario and focus on optimizing the efficiency and sustainability of the selected method.

Financial viability

Financial viability is one of the critical factors, alongside environmental and social sustainability, for selecting any treatment technology. Even if a technology effectively removes PFAS from water, lack of financially sustainability may limit adoption. All the papers we reviewed used net present value to assess the financial viability of their chosen treatment technologies. Researchers used the USEPA’s work breakdown structure model to evaluate the financial viability of IX and GAC for PFAS removal from groundwater, considering overall costs during their useful life^58,64. The life cycle inventory for each remediation system estimated lifetime costs in real dollars (i.e., USD). The cost variation between GAC and IX systems in different studies arises from several key factors, such as water type, flow rate, PFAS concentration, and media selection. For instance, in the case of AFFF-impacted groundwater with a flow rate of 0.038 million gallons per day (MGD) and 0.05 mg/L PFAS, the empty bed contact time was 10 minutes for GAC (Calgon F400) and 2 minutes for IX (PFAS-selective resin), resulting in total costs of per m³ of water treated in a year USD$0.50 for GAC and USD$0.28 for IX⁶⁴. In another study, using groundwater with a higher flow rate of 0.740 MGD and a lower PFAS concentration of 0.003 mg/L, the empty bed contact time was 7.5 minutes for GAC and 2 minutes for IX. The media used were Calgon F400 for GAC and strong base polystyrene gel-type II for IX, resulting in total costs of USD$367,000 for GAC and USD$225,000 for IX in a year⁵⁸. In both studies, one lag column (a secondary column used to capture any PFAS that breakthrough the lead column) was used, and PFOA and PFOS were the predominant PFAS considered. The higher flow rate and lower PFAS concentration in the second study required larger systems, increasing costs, while the media type and empty bed contact time also played significant roles in determining the total costs for each scenario. In both scenarios, the results show that the single-use IX system has lower capital costs compared to other systems due to lower media usage rates, longer operational life, and fewer required components (e.g., pumps, piping). While GAC media (Calgon F400) is generally cheaper than PFAS-selective resin, its high media usage rates and larger vessel requirements make it less economically viable than IX treatment for PFAS. Under the discussed scenario, single-use IX resin proves to be much more cost-effective than GAC. However, costs are likely to vary significantly based on changes in PFAS breakthrough criteria, flow rate, pretreatment requirements, and solute composition. A sensitivity analysis can help illustrate how adjustments to these decision variables influence the overall treatment costs, and GAC may prove to be cost-effective under certain technical design configurations.

The financial viability of multistage membrane technology for landfill leachate treatment compared offsite and onsite scenarios for PFAS compliance. Both the onsite and offsite scenarios in the study include pretreatment processes before membrane treatment and excluded the final fate of PFAS. The primary cost driver for onsite treatment is operational expenses (45%) due to high electricity and chemical usage, while leachate transportation accounts for 95% of offsite costs. Using 1 g of PFAS treated as the functional unit, the onsite scenario’s life cycle cost is 83% lower than the offsite scenario. However, treating 1 m³ of raw leachate costs $1.96 onsite compared to $2.50 offsite, reflecting a 21% cost reduction for onsite treatment despite its higher initial costs⁶¹. The net present values of a two-pass spiral-wound reverse osmosis system for additional leachate treatment in Thailand were $577.9 million USD for a system with an evaporation pond and $391.9 million USD for a system without one. Treatment unit costs ranged from $1.72 to $2.71 USD/m³ for the system with an evaporation pond and from $1.06 to $2.09 USD/m³ for the system without the pond depending on landfill size⁶⁸. The two-pass spiral-wound reverse osmosis system without an evaporation pond shows lower treatment unit costs ($1.06–$2.09 per m³) compared to the onsite multistage membrane technology ($1.96 per m³). Despite higher initial costs, the overall financial viability is better for the reverse osmosis system than onsite multistage membrane technology, especially without the evaporation pond. While each PFAS treatment technology has trade-offs, the single-use IX system and the two-pass spiral wound reverse osmosis system without an evaporation pond are more financially viable options for groundwater and landfill leachate treatment, respectively. These technologies offer lower costs per unit volume treated, and reduced operational expenses, making them more attractive for practical application. Media production, replacement, regeneration, and disposal are key drivers of operational costs in PFAS treatment, with water composition playing a crucial role in the breakthrough of IX resins or GAC. Similar to the environmental impact, water quality also affects costs; the presence of inorganic ions, NOM, and varying pH levels can accelerate media exhaustion, leading to more frequent replacement or regeneration. This process not only increases direct costs but also adds to indirect costs, such as labor and maintenance. Additionally, certain contaminants may necessitate pre-treatment processes, further raising overall expenses. Thus, incorporating water composition into financial assessments is essential to accurately forecast operational costs and evaluate the financial viability of the treatment process, alongside its environmental sustainability.

Social Impacts

The social impacts of PFAS treatment technologies remain under-researched, with each technology presenting unique social implications, such as equity, accessibility, public acceptance, and potential effects on community health. The primary social benefit is public health improvement due to PFAS removal from water sources. IX treatment effectively removes PFAS from groundwater, reducing exposure and lowering the risk of cancer and endocrine disruption. Similarly, GAC treatment significantly reduces PFAS levels in drinking water, decreasing the risk of cancer, liver damage, and thyroid disease. However, IX resin production and disposal pose social risks due to high ozone depletion potential, leading to respiratory issues, and ecological damage. Conversely, GAC releases higher levels of harmful emissions, including both carcinogens and non-carcinogens, compared to IX, which can negatively affect air quality and pose health risks to surrounding communities^58,63,64,67. Previous research highlights important distinctions between different PFAS treatment technologies, particularly in terms of health and social impacts. For example, IX has generally been found to result in higher life cycle human health impacts compared to GAC⁶⁷. These impacts are part of the treatment process itself and do not reflect the health benefits gained from the reduction of contaminants in the treated water. This suggests that GAC may be a more favorable option in contexts where minimizing health risks is a priority. Using the social sustainability evaluation matrix, studies have demonstrated that GAC is more socially sustainable than IX⁵⁸. The social sustainability evaluation matrix, an Excel-based tool, enables users to specify, and quantify the social aspects of a project by identifying key indicators for measurement. Its scoring system categorizes impacts into five sections: no impacts, positive, ideal, negative, and unacceptable. This comprehensive assessment framework helps highlight the social advantages of GAC over IX, reinforcing its potential benefits beyond just environmental considerations. In the context of landfill leachate treatment, the choice between onsite and offsite technologies has significant implications for human health. Research suggests that onsite multistage membrane technology may provide greater health benefits compared to offsite scenarios; however, further studies are needed to confirm these findings⁶¹. One of the main reasons could be the elimination of transportation risks and the ability to directly manage and optimize the treatment process. This leads to lower human health risks associated with PFAS exposure. This finding underscores the importance of location and technology integration in optimizing the health outcomes of treatment processes. These insights collectively emphasize the need for a holistic evaluation of PFAS treatment technologies, considering health, social, and logistical factors. By understanding these nuances, decision-makers can better select and implement technologies that align with broader sustainability goals.

Challenges to sustainability

Sustainability analysis of any treatment technologies evaluates their environmental, social, and financial impacts. Quantitative Sustainable Design (QSD) is a structured methodology used for accelerating and supporting the research, development, and deployment of technologies^118,119. QSD integrates concepts from sustainability science and engineering to facilitate the creation and implementation of sustainable solutions. A critical step in QSD is defining the problem space, which includes the selection of variables or parameters that influence sustainability, i.e., decision variables, technological parameters, and contextual parameters. Previous studies on the sustainability of PFAS treatment technologies primarily focus on GAC and IX. Figure 2 highlights the different inputs for GAC and IX. It focuses on their effects on environmental sustainability, social impacts, and financial viability. This figure can help future researchers to understand how decision variables, technological parameters, and contextual parameters affect sustainability. It can also guide the design of more sustainable PFAS treatment technologies for water sources.

Decision variables

Decision variables are independent inputs that can be controlled by the designer or operator¹¹⁹. For both GAC and IX technologies, an initial decision is whether to use single-use or reactivated/regenerable options. Single-use GAC has significant environmental impacts due to its high media usage rate and the need for frequent replacement and disposal. The frequent production, transportation, and disposal of GAC result in the release of harmful substances, including volatile organic compounds, particulate matter, and greenhouse gases. During incineration or landfill disposal, incomplete combustion can release toxic by-products such as carcinogens. These emissions can degrade air quality and increase health risks, including respiratory issues and cancer in nearby communities⁶⁴. In contrast, reactivating GAC media reduces these impacts by decreasing the demand for new media production; thus lowering resource consumption and waste generation. Reactivation processes also mitigate negative health impacts by reducing the frequency of GAC media replacement; thereby lowering emissions. Although the initial costs for reactivation infrastructure can be high, reactivated GAC is more cost-effective and environmentally sustainable than single-use GAC. This is particularly true at higher contaminant concentrations because reactivated GAC has lower operational costs for media replacement and disposal^64,67. Similarly, the choice between single-use and regenerable IX also significantly affects sustainability. Under similar experimental setup, both single use and regenerable IX have lower environmental impacts compared to single-use GAC, primarily due to their extended operational life and reduced media usage rate. However, the production phase of regenerable IX presents social risks, particularly high carcinogenic emissions, fossil fuel depletion, and global warming potential. These can lead to long-term health and environmental consequences^58,63,64,67. The type of sorbent used in GAC primarily affects environmental sustainability and financial viability. Media from different carbon sources have varying adsorption capacities and lifespans, which impact the frequency of replacement, resource consumption, and waste generation. Bituminous GAC is widely recognized in research as one of the most effective media for removing PFAS. However, there is still a lack of studies addressing its environmental sustainability and financial viability^{120,121,122,123}. Each decision variable can involve trade-offs across overall sustainability of the PFAS treatment technologies. Therefore, a comprehensive evaluation is necessary to optimize treatment outcomes.

Technological parameters

Technological parameters, inherent to a technology’s design and operations, significantly impact the sustainability of PFAS treatment systems, and are determined by the technology itself, not the designer or operator¹¹⁹. Effective PFAS treatment technologies require careful consideration of several key technological parameters, each of which impacts environmental sustainability, social impacts, and financial viability. For both IX and GAC, media production and incineration of spent media are the major sources of environmental impact. Media production for GAC requires activation processes and may involve mining (e.g., coal), which consumes high energy and release greenhouse gases, making this phase a major contributor to the environmental impact of GAC treatment systems. Similarly, the production of IX resins, particularly single-use resins, involves the synthesis of polymers. This process causes high environmental impacts, including ozone-depleting emissions⁶⁴. Incineration of spent media from both GAC and IX, especially when used as single-use, is energy-intensive (above 1100 °C for GAC) and results in emissions that contribute to global warming. Single-use IX systems have higher impacts from incineration compared to GAC. This is particularly applicable for human toxicity, cancer, eutrophication, and ecotoxicity due to the energy required for resin production. Incineration also involves high operational costs, increasing the financial burden of both GAC and IX treatment technologies^64,66. Effective management of spent media can mitigate these impacts. For instance, off-site thermal reactivation of GAC media reduces the need for new media production and minimizes waste, positively impacting environmental sustainability⁶⁴. However, the transportation and reactivation processes still contribute to environmental and social impacts. In IX systems, regenerating spent media involves handling and disposing of brine and cosolvents containing PFAS, which can cause significant environmental impacts and social risks due to the release of hazardous substances during incineration^63,64.

Empty bed contact time and bed volume are directly proportional, as empty bed contact time is calculated by dividing the bed volume by the flow rate. While both are critical in PFAS treatment system design, their impacts on sustainability and costs are intertwined. For GAC systems, which typically require longer empty bed contact time (around 10 minutes) compared to IX systems (2-3 min), this means larger bed volumes, resulting in higher energy use, greater material needs, and increased costs^58,64. In contrast, shorter empty bed contact time allow for smaller bed volumes in IX systems reduces energy and space requirements, making them more efficient environmentally and economically^58,64. Another critical parameter affecting the sustainability of PFAS treatment technologies is media usage rate. A higher media usage rate results in frequent media replacements, increased production, and greater disposal needs, which escalate the environmental footprint and raise operational costs. High media usage rates in GAC systems lead to frequent replacements. This increases media production and disposal needs, escalating both environmental impacts and operational costs. Meanwhile, lower media usage rates in IX systems extend media life. This reduces replacement frequency, minimizes environmental impacts and lowers costs⁶⁴. Optimizing media usage rate can balance operational efficiency and sustainability, reducing both environmental and financial impacts. The choice of activating agent in GAC significantly affects both environmental sustainability and financial viability. For example, optimizing sludge-based GAC adsorbents by reducing the activating agent (ZnCl₂) impregnation ratio can substantially lower environmental impacts and decrease production costs⁶². By understanding and optimizing these technological parameters, stakeholders can better balance the environmental sustainability, social impacts, and financial viability of PFAS treatment technologies. This comprehensive approach is essential for designing more sustainable solutions for PFAS removal from water sources.

Contextual parameters

Contextual parameters represent non-technological values that influence the sustainability of technologies, particularly during the deployment stage¹¹⁹. These parameters are designed to capture the specific circumstances in which the technology will be implemented. The length of PFAS chains significantly impacts the environmental sustainability, social impacts, and financial viability for both GAC and IX systems. IX resins were identified as a cost-effective adsorbent for removing both long and short-chain PFAS compared to GAC adsorbents³⁷. Previous research indicates that IX systems have a higher adsorption capacity than GAC and are more effective at removing long-chain PFAS, like PFOA and PFOS, compared to short-chain PFAS¹. Studies show that GAC also adsorbs long-chain PFAS better than short-chain PFAS¹²⁴. This indicates that both IX resins and GAC adsorbents exhibit higher adsorption capacity for long-chain PFAS compared to short-chain PFAS. In another study, sludge-based GAC exhibited the lowest removal rate (35.3–57.8%) for short-chain PFAS compounds, likely due to their high solubility and low hydrophobicity^125,126. Increasing the empty bed contact time can enhance the efficiency of GAC in removing short-chain PFAS, offering protection against the rapid breakthrough of short-chain PFAS^37,127. GAC and IX treatments require a longer empty bed contact time for short-chain PFAS compared to long-chain PFAS³⁷. Both long-chain and short-chain PFAS pose significant social impacts, primarily through health risks. Compared to long-chain PFAS, treating short-chain PFAS requires a higher media usage rate, which increases environmental impacts. This includes higher values for carcinogenic and non-carcinogenic effects, as well as global warming potential, indicating greater health damage compared to long-chain PFAS. Consequently, the treatment of short-chain PFAS may lead to higher overall environmental, social, and financial damage.

PFAS concentration is another important parameter that effects the sustainability. Both groundwater and bottled water were examined under a range of PFOA and PFOS concentrations covering three orders of magnitude (0.7, 7.0, and 70 μg/L) using both GAC adsorbents and IX resins. Higher PFAS concentrations significantly impact environmental sustainability and social health issues. As PFAS levels increase, greenhouse gas emissions from GAC-based treatment rise, reaching 0.54 and 2.7 kg CO₂eq/m³ H₂O at 7.0 and 70 μg/L PFAS, respectively^65,67. GAC media production and reactivation processes result in greater environmental impacts compared to IX-based treatments at higher contaminant levels. Energy consumption for GAC increases substantially, contributing to impacts such as fossil fuel depletion, respiratory effects, and smog formation. At high PFAS concentrations, electricity consumption contributes significantly to climate change impacts: 15% for GAC and 63% for IX treatment. Human health impacts are also heightened, with electricity production (mainly coal-fired) responsible for over 75-90% of health and ecotoxicity impacts from both GAC and IX systems. As PFAS concentrations rise from 0.7 to 70 μg/L, life cycle electricity consumption increases from 1.5 to 1.9 MJ/m³ for GAC and from 1.5 to 1.6 MJ/ m³ for IX, amplifying both health and environmental consequences⁶⁷.

Disposal options for spent media primarily impact environmental sustainability and financial viability. For GAC systems, the disposal of activated carbon significantly impacts acidification and ozone depletion. Additionally, incineration of spent media at high temperatures (above 1100 °C) results in substantial greenhouse gas emissions and other pollutants, contributing to global warming and degradation of air quality^64,66 Similarly, for IX systems, disposal of brine and cosolvents containing PFAS can lead to hazardous emissions during incineration, impacting both environmental and social sustainability due to potential health risks^64,65. Financially, incineration and other disposal methods incur high operational costs, increasing the overall treatment cost. Maintenance significantly impacts the financial viability of both GAC and IX systems. GAC systems face higher operational costs due to frequent media replacements, despite having lower annual operating and maintenance costs compared to IX systems⁵⁸. IX systems, while having higher initial capital costs, benefit from lower media usage rates and longer operational life, reducing the need for frequent replacements. While the regeneration process adds to IX operational costs, these systems are more cost-effective over time due to reduced maintenance needs. Effective maintenance strategies are essential to optimize the financial viability of both GAC and IX treatment technologies.

Infrastructure requirements significantly affect financial viability and environmental sustainability. Treatment systems need contactors, pipes, fittings, and corrosion-resistant coatings. The infrastructure for resin treatment and regeneration is assumed to be twice as complex as that for GAC due to its added components⁶⁷. Despite its reusability, regenerable IX is the second most impactful system after single-use GAC because of the additional infrastructure and chemical-intensive regeneration processes⁶⁴. Although capital impacts are generally minimal, they are significant for single-use IX due to its low media usage rates. For reactivated GAC, the absence of high-temperature incineration shifts more impact to infrastructure requirements for regeneration. Energy consumption significantly affects the financial viability and environmental sustainability of PFAS treatment technologies. High energy use increases production costs, making technologies less efficient. GAC adsorbents production and reactivation consume substantial energy, leading to higher life cycle impacts like fossil fuel depletion and respiratory effects⁶⁷. Thermal reactivation of GAC adsorbents, at 815 °C, is less energy-intensive than incineration at 1200 °C, making it more cost-effective^64,66. Regenerable IX systems also increase energy demand due to the salts used in regeneration, especially those derived from chemicals(e.g., NH₄Cl, K₂CO₃)⁶³. Both GAC and IX systems are sensitive to local electricity grid variations, affecting costs and environmental impacts. For example, electricity prices vary from 5.07 cents per kilowatt-hour (kWh) in Oklahoma to 35.86 cents/kWh in Hawaii, and GHG emissions from electricity range widely¹²⁸. Switching to renewable energy sources, like wind or solar, can significantly reduce human health costs and global warming potential, making renewable energy a key target for cost and impact reduction.

Charting pathways for sustainable treatment of PFAS

The new U.S. EPA regulation requires public water systems to complete initial monitoring of six PFAS, including PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and mixtures containing at least two or more of PFHxS, PFNA, HFPO-DA, and PFBS by 2027¹²⁹. If the concentration of these PFAS exceeds the maximum contaminant levels (MCL), solutions to reduce their concentrations must be implemented by 2029. The U.S. EPA estimates that the new regulation will reduce PFAS exposure for about 100 million Americans, leading to fewer cases of cancer, liver disease, and birth complications. This will result in annual health benefits of approximately $1.5 billion, covering reduced medical costs and lost income¹³⁰. However, the actual benefits may be even higher, considering unquantified health effects like developmental and cardiovascular issues as well as the potential for removing other emerging pollutants during PFAS treatment that are not yet the focus of current regulations. While, according to AWWA, the national cost for treating long-chain PFAS (PFOA, PFOS, PFHxS, PFHpA, and PFNA) at a 4 ppt level is approximately $60 billion in the United States. This underscores the need for sustainable and cost-effective PFAS treatment technologies that effectively remove these contaminants from water¹³¹. As current situation demands sustainable treatment technologies to eliminate persistent PFAS from water sources, comprehensive sustainability studies are required. These studies must encompass existing technologies and explore new solutions under various scenarios, including different water types, indicators of sustainability, prioritization and weighting of the indicators. To navigate the extensive opportunity space for sustainable PFAS treatment, it is mandatory to integrate sustainability analyses throughout the research, development, and deployment phases of technologies. Our review of existing literature on PFAS water treatment technologies has led to the development of a proposed framework for understanding sustainable PFAS treatment (Fig. 3). The initial step in the sustainable treatment of PFAS involves identifying the type of water requiring treatment, e.g., groundwater, wastewater, drinking water, tap water, or fire extinguishing water. The performance of treatment systems like GAC and IX for PFAS removal was significantly influenced by the presence of co-existing chemical pollutants in water samples. These competing substances, such as NOM, inorganic ions, and other organic contaminants, occupied the active sites on GAC or IX resins, reducing their available capacity for PFAS adsorption. For instance, inorganic anions such as sulfate, chromate, and chloride competed with PFAS for adsorption sites on IX resins, impacting removal efficiency^132,133. High NaCl concentrations also reduced PFHxS adsorption by around 30%¹³⁴. These effects suggested that non-electrostatic mechanisms, such as physisorption and molecular aggregation, played a key role in PFAS removal. The impact of inorganic ions was expected to be more pronounced for short-chain PFAS, which rely more on electrostatic interactions for removal¹¹³. Dissolve organic carbon (DOC), a key component of NOM, in water competed with PFAS for adsorption sites on GAC and IX resins, reducing PFAS removal efficiency^135,136. In many studies, GAC performance was negatively impacted by the presence of co-existing organic matter, with its efficiency declining as DOC concentrations increased^{137,138,139,140}. Conversely, GAC adsorption capacity did not significantly decrease in the presence of NOM, likely due to the high PFAS concentration (50 mgL⁻¹) and the influence of ionic strength^45,141,142. This variation might be attributed to differences in experimental setups, including PFAS initial concentration, DOC source and concentration, empty bed contact time, and the type of activated carbon used. Polyacrylic resins, which were more effective at removing DOC, experience greater reductions in PFAS removal compared to polystyrene resins¹⁴³. The presence of 2–8 mg/L DOC reduced PFAS removal by up to 50 percentage points¹³⁷. Therefore, water chemistry highly impact the PFAS removal efficiency¹⁴⁴ thus impacting on environmental and financial sustainability. Each water type presents unique challenges and necessitates different treatment approaches. Based on the water type, appropriate treatment methods, such as IX, GAC, reverse osmosis, or other technologies, are selected. Next, inputs are specified, including decision variables (e.g., single-use or regenerable media), technological parameters (e.g., media production, bed volume), and contextual parameters (e.g., PFAS length, concentration). Sustainability is assessed across three primary indicators: environmental sustainability, financial viability, and social impacts. Tools such as TEA, LCA, and others are employed to evaluate these indicators. Models like MIVES integrate results from environmental, financial, and social assessments⁵⁸. The prioritization of indicators through ranking and weighting guides the final sustainability assessment. For example, the MIVES model was used to integrate results from environmental, financial, and social assessments for GAC and IX under different weighting scenarios. The scenarios included equal weighting of all indicators (33% each), higher weighting on social impacts (60%), and higher weighting on financial viability (50%). The results suggested that IX treatment is generally more sustainable than GAC treatment⁵⁸.

GAC and IX effectively adsorb PFAS, but their disposal or regeneration can lead to secondary pollution, such as harmful byproducts from incineration. Similarly, destruction technologies like advanced oxidation processes, electrochemical oxidation, and plasma treatments may generate persistent, harmful byproducts, including short-chain PFAS, requiring further studies to assess their long-term environmental impact. By using our proposed framework (Fig. 3), important factors can be considered to guide the identification of the most sustainable treatment technology for specific scenarios. If the results do not meet environmental guidelines or financial constraints, we can revisit any point in the proposed framework and choose alternative options. This framework is iterative, allowing for adjustments in treatment methods and re-prioritization of indicators. This iterative approach ensures the selection of sustainable and effective PFAS treatment method for particular water and contaminant types. Each treatment technology involves trade-offs, and our proposed framework supports sustainable PFAS treatment by guiding the evaluation of both established and emerging technologies. For established methods like GAC and IX, historical data and proven methods are used to specify inputs, assess sustainability, and optimize execution. However, the limitations of GAC and IX in different water matrices, such as reduced efficiency in the presence of competing contaminants, highlight the need to explore alternative technologies. Emerging methods like electrochemical treatment, advanced oxidation processes, and thermal treatment offer promising solutions by breaking down PFAS molecules rather than just adsorbing them. While these methods hold potential, they also come with challenges, such as high energy consumption and the generation of harmful byproducts. The U.S. EPA’s three R’s (Research, Restrict, and Remediate) are central to addressing PFAS, and our study finds that research into the sustainability of both established and emerging technologies for PFAS treatment is still in its developmental stages^77,145. Additionally, existing sustainability studies on treatments like GAC and IX are limited, as they rarely examine all three sustainability parameters: environmental sustainability, social impacts, and financial viability. Current literature primarily investigates PFAS concentrations within the microgram per liter (µg/L) range; however, PFAS levels in drinking water, groundwater, and wastewater are typically found at much lower concentrations, often in the nanogram per liter (ng/L) range. Future research should focus on investigating how different treatment media, such as GAC or IX resins, perform under varying PFAS concentrations, water quality conditions, and PFAS types. Future research should focus on investigating how different treatment media, such as GAC or IX resins, perform under varying water quality conditions, PFAS concentrations, and PFAS types. Such work is crucial for understanding the environmental, financial, and social sustainability of these technologies. Additionally, studies should examine the potential for secondary pollution risks, especially during the disposal or regeneration of these media. Further investigation into alternative emerging technologies like reverse osmosis, nanotechnology, electrochemical oxidation, and advanced oxidation processes is needed to evaluate their long-term effectiveness and feasibility in providing comprehensive PFAS treatment solutions across diverse scenarios. While PFAS toxicity is a major concern for human health and ecosystems, it’s essential to consider the environmental trade-offs of removal technologies like GAC and IX, which contribute to carbon emissions and climate change. This point raises the question for future studies of whether PFAS toxicity or climate impact is more pressing, calling for a balanced evaluation of treatment technologies that considers health, environmental, financial, and social factors. This review underscores the uncertainties in sustainability indicators and the trade-offs within different treatment systems. Overall, this study highlights the potential to reveal the sustainability implications of PFAS removal technologies in specific contexts. This enables stakeholders to make informed decisions about the multidimensional effects of these technologies, ultimately contributing to society’s transition towards greater sustainability.