Submission: February 07, 2024; Published: February 22, 2024

*Corresponding Author: Lin Wanga, Department of Civil Engineering, New Mexico State University, S Espina St, Las Cruces, New Mexico, United States

How to cite this article: Lin Wanga*, Runwei Li, Yun Ma, Dulith Rajapakshe and Shicheng Zhan. A Mini-Review of The Adsorptive Removal of Poly- And Perfluoroalkyl Substances (PFAS). Civil Eng Res J. 2024; 14(3): : 555890. DOI 10.19080/CERJ.2024.14.555890

Abstract

In recent years, per- and poly-fluoroalkyl substances (PFAS) have been frequently detected in aquatic environments, posing a serious threat to environmental safety and human health due to their persistence, bioaccumulation, and toxicity. Several technologies are available for PFAS remediation, including adsorption, advanced oxidation, nanofiltration, and microbial degradation. Among these strategies, adsorption is effective, affordable, and easy to access, and therefore has been recommended by the U.S. Environmental Protection Agency. This article reviews the adsorption behaviors between various PFAS and different adsorptive materials, such as activated carbon, resin, minerals, and biosorbents. In addition, this article provides fundamental knowledge of adsorption and an understanding of the difference between adsorptive materials.

Keywords: Adsorption; Active carbon; Resin; Minerals; Biosorbent; Molecularly imprinted polymer

Introduction

Per- or polyfluoroalkyl compounds (PFAS) are compounds produced by replacing all or part of the hydrogen atoms connected to the carbon in the molecules of organic compounds with fluorine atoms [1]. The carbon-fluorine (C-F) bond is the strongest single bond in chemistry and provides PFAS chemicals with high thermal and chemical stability. PFAS contain both hydrophilic functional groups (e.g., sulfonate groups and carboxyl groups) and hydrophobic and oleophobic C-F chains in the structure, and therefore can resist water, oil, and grease [2,3]. Due to their good performance and production suitability, PFAS are widely used in food packaging, textiles, semiconductors metal plating, fire-fighting foam, and other fields [4-6]. In the current decade, traditional PFAS with evidenced toxicity have been phased out due to the raising of public awareness and updated regulations. However, many new PFAS have been produced and widely used as substitutes of banned PFAS, including conventional short-chain PFAS (e.g., Perfluorobutanesulfonic acid, PFBS) and newly identified fluorinated replacements (e.g., Chlorinated polyfluoroalkyl ether sulfonic acids, Cl-PFESAs) [7]. However, several studies have shown that short-chain PFAS compounds are characterized by significant cytotoxicity and potential developmental toxicity, strong environmental persistence, and long-range transport [8-10]. Some of these compounds have similar or even higher bioaccumulation and toxicological effects than traditional PFAS [11-13]. Therefore, emerging PFAS alternatives, including short-chain analogs, precursors, and alternatives, have attracted increasing attention in environmental and ecotoxicological sciences in recent years. Adsorption is a promising technology for removing PFAS from water. Many studies have reported the adsorption and removal of PFAS by various adsorbents, including activated carbon, anion-exchange resins, and biomaterials, and have also investigated the adsorption mechanism of adsorbents on PFAS and its main influencing factors.

Adsorption for PFAS removal

Active Carbon

Activated carbon is one of the most used adsorbents in water treatment, which has been applied to the removal of a variety of pollutants due to its large specific surface area, well-developed pore structure, low cost, and wide range of material sources. It was reported that the structure of PFAS has a strong influence on the adsorption and removal effect, the longer the carbon chain of PFAS, the easier it is to be adsorbed, and the sulfonic acid PFAS is more likely to be adsorbed onto GAC than the carboxylic acid PFAS. This is since long-chain PFAS are more hydrophobic, and the sulfonic acid functional group has a stronger electrostatic attraction than the carboxylic acid functional group.

Resin

Resins, including ion-exchange resins and nonion-exchange resins, have the advantages of good chemical stability, and strong regeneration ability. In terms of adsorption performance and in situ regeneration, anion exchange resins are the most effective adsorbents for PFAS removal [17]. Generally, the anion-exchange resin has permanent positive charge exchange sites on its surface and thus has a high adsorption performance for PFAS [18]. Nonion exchange resins absorb PFAS mainly through hydrophobic interactions and van der Waals forces. Compared with anionexchange resins, they are easier to regenerate, but the adsorption performance is much lower than that of anion-exchange resins, so anion-exchange resins Resin is more widely used in practical applications [19].

Minerals

Mineral materials with high surface area, adjustable mesopores, and variable lamellar structure are considered to be suitable materials for the adsorption of PFAS [20]. The mineral materials used for PFAS removal are classified into layered clay minerals (kaolinite, montmorillonite, etc.) and amorphous clay minerals (acicular ferrite, magnetite, hematite, etc.) [21]. pH is a key factor in the removal of PFAS from water. Solution pH can affect the adsorption of PFAS by changing the morphology of PFAS and the surface charge of the mineral material [22].

Biosorbent

Bio-based adsorbent materials prepared from biomass through a series of physical and chemical modifications show great potential for removing pollutants from water due to their higher adsorption properties [23]. Biochar and chitosan are bio-based materials that have been widely used for the removal of PFAS. Biochar and activated carbon have similar adsorption properties for PFAS, and biochar is becoming a sustainable alternative to activated carbon in recent years due to its environmental friendliness [24]. Chitosan contains many amino, acetylamino, primary hydroxyl, and secondary hydroxyl groups, which makes it an excellent chelating site for PFAS, and has great potential in the remediation of PFAS-contaminated water [25].

Molecularly imprinted polymer (MIP)

Wastewater contains many compounds and colloids, and the concentration of these coexisting substances is generally higher than that of PFAS, which makes it easy to compete with PFAS for adsorption, leading to a decrease in the removal rate. Therefore, the selectivity of adsorption is very important for the removal of PFAS in water [26]. Deng et al. prepared MIP adsorbents with high selectivity, which increased the adsorption of PFOS by more than 1-fold compared with non-imprinted polymer (NIP) [27]. This was attributed to the high selectivity of the MIP adsorbent for PFOS, while the NIP adsorbent showed a decrease in adsorption due to competitive adsorption.

Conclusions and future work

This work provides fundamental knowledge of the behavior of adsorption. Adsorption is one of the most efficient and economical technologies for removing PFAS from water. In order to control the pollution of PFAS in water, future research could focus on the following topics:

i. Develop advanced materials with adsorption and synergistic degradation functions to achieve simultaneous enrichment and mineralization of PFAS, extend the service life of adsorbents, and improve PFAS removal efficiency.

ii. Develop an efficient adsorbent regeneration technology to solve the problems of low adsorption efficiency and the generation of secondary pollutants.

Acknowledgment

This material is based upon work supported by the U.S. Geological Survey under Grant/Cooperative Agreement No. G21AP10635. This project is funded by (1) the U.S. Geological Survey Water Resources Research Act 104b grant through the New Mexico Water Resources Research Institute’s annual base award, and (2) the New Mexico Water Resources Research Institute grant NMWRRI-SG-FALL2023 with the New Mexico State Legislature. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Geological Survey or the New Mexico State Legislature. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey and the New Mexico State Legislature.

References

1. Du ZW, Deng SB, Bei Y, Huang Q, Wang B, et al. (2014) Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents-A review. J Hazardous Materials 274: 443-454.
2. Dixit F, Dutta R, Barbeau B, Berube P, Mohseni M (2021) PFAS removal by ion exchange resins: A review. Chemosphere 272: 129777.
3. Zenobio JE, Salawu OA, Han ZW, Adeleye AS (2022) Adsorption of per- and polyfluoroalkyl substances (PFAS) to containers. J Hazardous Materials Adv 7: 100130.
4. Boyer TH, Fang YD, Ellis A, Dietz R, Choi YJ, et al. (2021) Anion exchange resin removal of per- and polyfluoroalkyl substances (PFAS) from impacted water: A critical review. Water Res 200: 117244.
5. Gao YX, Deng SB, Du ZW, Liu K, Yu G (2017) Adsorptive removal of emerging polyfluoroalky substances F-53B and PFOS by anion-exchange resin: A comparative study. J Hazardous Materials 323: 550-557.
6. Karbassiyazdi E, Kasula M, Modak S, Pala J, Kalantari M, et al. (2023) A juxtaposed review on adsorptive removal of PFAS by metal-organic frameworks (MOFs) with carbon-based materials, ion exchange resins, and polymer adsorbents." Chemosphere, 311: 136933.
7. Podder A, Sadmani A, Reinhart D, Chang NB, Goel R (2021) Per and poly-fluoroalkyl substances (PFAS) as a contaminant of emerging concern in surface water: A transboundary review of their occurrences and toxicity effects. J Hazardous Materials 419: 126361.
8. Li Y, Fletcher T, Mucs D, Scott K, Lindh CH, et al. (2018) Half-lives of PFOS, PFHxS and PFOA after end of exposure to contaminated drinking water. Occup Environ Med 75(1): 46-51.
9. Olsen GW, Chang SC, Noker PE, Gorman GS, Ehresman DJ, et al. (2009) A comparison of the pharmacokinetics of perfluorobutanesulfonate (PFBS) in rats, monkeys, and humans. Toxicol 256(1-2): 65-74.
10. Worley RR, Moore SM, Tierney BC, Ye XY, Calafat AM, et al. (2017) Per- and polyfluoroalkyl substances in human serum and urine samples from a residentially exposed community. Environ Int 106: 135-143.
11. Liu SY, Yang RJ, Yin NY, Faiola F (2020) The short-chain perfluorinated compounds PFBS, PFHxS, PFBA and PFHxA, disrupt human mesenchymal stem cell self-renewal and adipogenic differentiation. J Environ Sci 88: 187-199.
12. Conder JM, Hoke RA, De Wolf W, Russell MHm, Buck RC (2008) Are PFCAs bioaccumulative? A critical review and comparison with regulatory lipophilic compounds. Environ Sci Techn 42(4): 995-1003.
13. Munoz G, Liu JX, Duy SV, Sauvé S (2019) Analysis of F-53B, Gen-X, ADONA, and emerging fluoroalkylether substances in environmental and biomonitoring samples: A review. Trends Environ Analytical Chem 23: e00066.
14. Du ZW, Deng SB, Zhang SY, Wang B, Huang J, et al. (2016) Selective and High Sorption of Perfluorooctanesulfonate and Perfluorooctanoate by Fluorinated Alkyl Chain Modified Montmorillonite. J Phys Chem 120(30): 16782-16790.
15. Xiao LL, Ling YH, Alsbaiee A, Li CJ, Helbling DE, et al. (2017) β-Cyclodextrin Polymer Network Sequesters Perfluorooctanoic Acid at Environmentally Relevant Concentrations. J Am Chem Soc 139(23): 7689-7692.                        
16. Yu Q, Zhang RQ, Deng SB, Huang J, Yu G (2009) Sorption of perfluorooctane sulfonate and perfluorooctanoate on activated carbons and resin: Kinetic and isotherm study. Water Res 43(4): 1150-1158.
17. Zhang DQ, Zhang WL, Liang YN (2019) Adsorption of perfluoroalkyl and polyfluoroalkyl substances (PFASs) from aqueous solution - A review. Sci Total Environ 694: 133606.
18. Yu H, Chen H, Fang B, Sun HW (2023) Sorptive removal of per- and polyfluoroalkyl substances from aqueous solution: Enhanced sorption, challenges and perspectives. Sci Total Environ 861: 160647.
19. Ross I, McDonough J, Miles J, Storch P, Kochunarayanan PT, et al. (2018) A review of emerging technologies for remediation of PFASs. J Environ Cleanup Costs Technologies & Techniques 28(2): 101-126.
20. Feng Y, Zhou Y, Lee PH, Shih KM (2016) Mineralization of perfluorooctanesulfonate (PFOS) and perfluorodecanoate (PFDA) from aqueous solution by porous hexagonal boron nitride: adsorption followed by simultaneous thermal decomposition and regeneration. Rsc Advances 6(114): 113773-113780.
21. Barakan S, Aghazadeh V (2021) The advantages of clay mineral modification methods for enhancing adsorption efficiency in wastewater treatment: a review. Environ Sci Pollution Res 28(3): 2572-2599.
22. Zhang RM, Yan W, Jing CY (2014) Mechanistic study of PFOS adsorption on kaolinite and montmorillonite. Colloids and Surfaces a-Physicochem Eng Aspects 462: 252-258.
23. Rayne S, Forest K (2009) Perfluoroalkyl sulfonic and carboxylic acids: A critical review of physicochemical properties, levels and patterns in waters and wastewaters, and treatment methods. J Environ Sci Health Part a-Toxic/Hazardous Substan Environ Eng 44(12): 1145-1199.
24. Du ZW, Deng SB, Chen YG, Wang B, Huang J, et al. (2015) Removal of perfluorinated carboxylates from washing wastewater of perfluorooctanesulfonyl fluoride using activated carbons and resins. J Hazardous Materials 286: 136-143.
25. Elanchezhiyan SS, Preethi J, Rathinam K, Njaramba LK, Park CM (2021) Synthesis of magnetic chitosan biopolymeric spheres and their adsorption performances for PFOA and PFOS from aqueous environment. Carbohydrate Polymers 267: 118165.
26. Deng SB, Shuai DM, Yu Q, Huang J, Yu G (2009) Selective sorption of perfluorooctane sulfonate on molecularly imprinted polymer adsorbents. Front Environ Sci Eng China 3(2): 171-177.
27. Yu Q, Deng SB, Yu G (2008) Selective removal of perfluorooctane sulfonate from aqueous solution using chitosan-based molecularly imprinted polymer adsorbents. Water Res 42(12): 3089-3097.