Effect of effluent organic matter on the adsorption of perfluorinated compounds onto activated carbon

Adsorption of typical NDMA precursors by superfine powdered activated carbon: Critical role of particle size reduction

Control of N-nitrosodimethylamine (NDMA) in drinking water could be achieved by removing its precursors as one practical way. Herein, superfine powdered activated carbons with a diameter of about 1 µm (SPACs) were successfully prepared by grinding powdered activated carbon (PAC, D50=24.3 µm) and applied to remove model NDMA precursors, i.e. ranitidine (RAN) and nizatidine (NIZ). Results from grain diameter experiments demonstrated that the absorption velocity increased dramatically with decreasing particle size, and the maximum increase in k2 was 26.8-folds for RAN and 33.4-folds for NIZ. Moreover, kinetic experiments explained that rapid absorption could be attributed to the acceleration of intraparticle diffusion due to the shortening of the diffusion path. Furthermore, performance comparison experiments suggested that the removal of RAN and NIZ (C0=0.5 mg/L) could reach 61.3% and 60%, respectively, within 5 min, when the dosage of SAPC-1.1 (D50=1.1 µm) was merely 5 mg/L, while PAC-24.3 could only eliminate 17.5% and 18.6%. The adsorption isotherm was well defined by Langmuir isotherm model, indicating that the adsorption of RAN/NIZ was a monolayer coverage process. The adsorption of RAN or NIZ by SAPC-1.1 and PAC-24.3 was strongly pH dependent, and high adsorption capacity could be observed under the condition of pH > pka+1. The coexistence of humic acid (HA) had no significant effect on the adsorption performance because RAN/NIZ may be coupled with HA and removed simultaneously. The coexistence of anions had little effect on the adsorption also. This study is expected to provide an alternative strategy for drinking water safety triggered by NDMA.

Interaction and coexistence characteristics of dissolved organic matter and toxic metals with per- and polyfluoroalkyl substances in landfill leachate

Landfill leachate-containing per- and polyfluoroalkyl substances (PFAS) is both an important 'sink' and a 'source' of secondary pollution, posing serious threaten to surrounding environments. To date, the pollution characteristics of PFAS in landfill leachate, and the coexistence and interaction between PFAS and other leachate contaminants, such as dissolved organic matter (DOM) and toxic metals remains unclear. Herein, our results showed that 17 target PFAS, with concentrations ranged from 1804 to 43309 ng/L, were detected in landfill leachates. The main PFAS were short-chain and even-chain substances represented by perfluorobutanoic acid (PFBA) and perfluorobutane sulfonic acid (PFBS). Leachate derived DOM is mainly composed of protein-like and humic-like substance, among which the total contribution of protein-like substance is as high as 73.7%. Correlation analysis results showed that the distribution of PFAS was strongly correlated with the substituted functional groups (e.g., carboxyl and hydroxyl) on the aromatic ring of humic-like substance (C2 and E253/E203) and autochthonous metabolism by microbial activities (FI). Furthermore, Mn element showed a significantly strong correlation with PFAS. Both organic and inorganic substances positively correlated with toxic metals. Our findings are helpful to understand the environmental fate of PFAS, and contribute to decision-making regarding DOM, toxic metals, and PFAS management in landfill.

Causative mechanisms limiting the removal efficiency of short-chain per- and polyfluoroalkyl substances (PFAS) by activated carbon

Short-chain per and polyfluoroalkyl substances (PFAS) have been found to be relatively high in water treatment systems compared to long-chain PFAS because of the unsatisfactory adsorption efficiency of short-chain PFAS. Knowledge about why short-chain PFAS are less removed by porous carbon is very limited. The study focused on providing causal mechanisms that link the low adsorption of short-chain PFAS and proposing an improved method for removing both short- and long-chain PFAS. The long-chain PFAS with higher hydrophobicity diffused more quickly than the short-chain PFAS due to stronger partitioning driving forces. In the initial adsorption stage, therefore, pores of activated carbon were blocked by long-chain PFAS, which makes it difficult for the short-chain PFAS to enter the internal pores. Although several short-chain PFAS diffuse into the pores, the relatively more hydrophilic short-chain congeners cannot be fully adsorbed on activated carbon due to limited positively charged sites. Moreover, compared to larger particle sizes, smaller activated carbon particles have shorter pore channels near the surface, reducing the risk of pore-blocking and ensuring the pores remain accessible for more efficient adsorption. Additionally, these smaller particles offer a greater external surface area and more functional groups, which enhance the adsorption capacity. It indicates that the smaller particle size of activated carbon would have a positive effect on the short-chain PFAS removal.

Rejection of PFAS and priority co-contaminants in semiconductor fabrication wastewater by nanofiltration membranes

Use of high-pressure membranes is an effective means for removal of per-and polyfluoroalkyl substances (PFAS) that is less sensitive than adsorption processes to variable water quality and specific PFAS structure. This study evaluated the use of nanofiltration (NF) membranes for the removal of PFAS and industry relevant co-contaminants in semiconductor fabrication (fab) wastewater. Initial experiments using a flat sheet filtration cell determined that the NF90 (tight NF) membrane provided superior performance compared to the NF270 (loose NF) membrane, with NF90 rejection values exceeding 97 % for all PFAS evaluated, including the ultrashort trifluoromethane sulfonic acid (TFMS). Cationic fab co-contaminants diaryliodonium (DIA), triphenylsulfonium (TPS), and tetramethylammonium hydroxide (TMAH) were not as highly rejected as anionic PFAS likely due to electrostatic effects. A spiral wound NF90 module was then used in a pilot system to treat a lab solution containing PFAS and co-contaminants and fab wastewater effluent. Treatment of the fab wastewater, containing high concentrations of perfluorocarboxylic acids (PFCAs), including trifluoroacetic acid (TFA: 96,413 ng/L), perfluoropropanoic acid (PFPrA: 11,796 ng/L), and perfluorobutanoic acid (PFBA: 504 ng/L), resulted in ≥92 % rejection of all PFAS while achieving 90 % water recovery in a semi-batch configuration. These findings demonstrate nanofiltration as a promising technology option for incorporation in treatment trains targeting PFAS removal from wastewater matrices.

Impacts of polystyrene nanoplastics on microgel formation from effluent organic matter

Municipal effluents discharged from wastewater treatment plants (WWTPs) are considered major contributors of nanoplastics (NPs) and dissolved effluent organic matter (dEfOM) to environments. Due to their small sizes, NPs can travel easily in waterways and evade wastewater treatment processes, and may directly interact with dEfOM, altering their environmental fates. However, although much research has examined the impact of natural organic matter on NPs, the interactions between NPs and dEfOM remain unexplored. This study investigated the influences of NPs on the behavior and capacity of dEfOM aggregation and surface granularity, and identified the possible aggregation mechanism. We also adjusted the salinity of water samples to simulate scenarios based on WWTP-sea continuums. Our data suggest that dEfOM can self-assemble with 55 nm polystyrene NPs to form microgels, particularly under high salinity conditions. NPs accelerates the formation speed and number of dEfOM aggregates, but the sizes of the aggregates remain largely unchanged. The relative particle counts at a salinity of 34 psu increased by 300 % compared to the control group. The potential mechanism behind NPs-microgels aggregation is likely driven by the synergistic effect of the divalent ion crosslinking and hydrophobic interactions between EfOM and NPs. Notably, NPs incorporation into microgels decreases the surface granularity, thereby possibly affecting settling velocity and colonization of aggregates, as well as microbial attachment and community diversity. Overall, our findings demonstrate the potential influence of NPs on dEfOM assembly and surface properties following effluent discharge, and can inspire further relevant studies on microorganism interactions, removal technologies, and the environmental transport of NPs.

A review of per- and polyfluoroalkyl substances (PFASs) removal in constructed wetlands: Mechanisms, enhancing strategies and environmental risks

PER: Polyfluoroalkyl substances (PFASs), typical persistent organic pollutants detected in various water environments, have attracted widespread attention due to their undesirable effects on ecology and human health. Constructed wetlands (CWs) have emerged as a promising, cost-effective, and nature-based solution for removing persistent organic pollutants. This review summarizes the removal performance of PFASs in CWs, underlying PFASs removal mechanisms, and influencing factors are also discussed comprehensively. Furthermore, the environmental risks of PFASs-enriched plants and substrates in CWs are analyzed. The results show that removal efficiencies of total PFASs in various CWs ranged from 21.3% to 98%. Plant uptake, substrate absorption and biotransformation are critical pathways in CWs for removing PFASs, which can be influenced by the physiochemical properties of PFASs, operation parameters, environmental factors, and other pollutants. Increasing dissolved oxygen supply and replacing traditional substrates in CWs, and combining CWs with other technologies could significantly improve PFASs removal. Further, CWs pose relatively lower ecological and environmental risks in removing PFASs, which indicates CWs could be an alternative solution for controlling PFASs in aquatic environments.

Comparison of perfluoroalkyl substance adsorption performance by inorganic and organic silicon modified activated carbon

Owing to the persistence and increasingly stringent regulations of perfluoroalkyl substances (PFAS), it is necessary to improve their adsorption capacities using activated carbon (AC). However, their adsorption capacities are suppressed by dissolved organic matter (DOM). In this study, two ACs modified with organic silicon (C-OS) and inorganic silicon (C-IS) were synthesized and used for the adsorption of PFAS in raw water (RW). The results showed that the PFAS adsorption capacity of C-IS was much less influenced by DOM than that of the original AC (C-virgin). In RW, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) adsorption capacities on C-IS were 15.08 and 3.65 times higher than those on C-virgin, respectively. DOM had less influence on the PFOA and PFOS adsorption kinetics of C-IS than C-OS and C-virgin. Under multi-PFAS condition, C-IS also exhibited slower desorption of short-chain PFAS and breakthrough in batch and column tests, respectively. Characterization of the ACs before and after adsorption and independent gradient modelling indicated that hydrogen bond interactions between the O-Si of C-IS and the -COOH or -CSO3H groups of PFAS contributed to PFAS adsorption. Density functional theory calculations demonstrated that the adsorption energy of C-IS was much lower than that of C-OS and C-virgin. The arrangement of PFAS molecules on C-OS was chaotic owing to the hydrophobic siloxane chain, whereas the arrangement of PFAS on C-IS was orderly in multi-layer or semi-micelle status and more favorable to PFAS adsorption. This study provides a new strategy for avoiding adverse effects of DOM on PFAS adsorption.

Perfluoroalkyl acid adsorption by styrenic β-cyclodextrin polymers, anion-exchange resins, and activated carbon is inhibited by matrix constituents in different ways

Perfluoroalkyl acids (PFAAs) are ubiquitous environmental contaminants of global concern, and adsorption processes are the most widely used technologies to remove PFAAs from water. However, there remains little data on the ways that specific water matrix constituents inhibit the adsorption of PFAAs on different adsorbents. In this study, we evaluated the adsorption of 13 PFAAs on two styrene-functionalized β-cyclodextrin (StyDex) polymers, an activated carbon (AC), and an anion-exchange resin (AER) in the absence and presence of specific water matrix constituents (16 unique water matrices) in batch experiments. All four adsorbents exhibited some extent of adsorption inhibition in the presence of inorganic ions and/or humic acid (HA) added as a surrogate for natural organic matter. Two PFAAs (C5-C6 perfluorocarboxylic acids (PFCAs)) were found to exhibit relatively weak adsorption and five PFAAs (C6-C8 perfluorosulfonic acids (PFSAs) and C9-C10 PFCAs) were found to exhibit relatively strong adsorption on all four adsorbents across all matrices. Adsorption inhibition was the greatest in the presence of Ca2+ (direct site competition) and HA (direct site competition and pore blockage) for AC, NO3- (direct site competition) and Ca2+ (chemical complexation) for the AER, and SO42- (compression of the double layer) for the StyDex polymers. The pattern of adsorption inhibition of both StyDex polymers were similar to each other but different from AC and AER, which demonstrates the distinctive PFAA adsorption mechanism on StyDex polymers. The unique performance of each type of adsorbent confirms unique adsorption mechanisms that result in unique patterns of adsorption inhibition in the presence of matrix constituents. These insights could be used to develop models to predict the performance of these adsorbents in real water matrices and afford rational selection of adsorbents based on water chemistry for specific applications.

Molecular Interactions of Perfluorinated and Branched Fluorine-Free Surfactants at Interfaces: Insights from a New Reliable Force Field

Per- and polyfluoroalkyl substances (PFAS) constitute a class of synthetic compounds with exceptional interfacial properties. Their widespread use in many industrial applications and consumer products, combined with their remarkable chemical and thermal stability, has led to their ubiquitous presence in environmental matrices, including surface water and groundwater. To replace PFAS with fluorine-free surfactants, it is necessary first to develop a deep molecular-level understanding of the mechanisms responsible for the exceptional properties of PFAS. For instance, it has been shown that fluorine-free surfactants with highly branched or methylated chains can achieve low surface tensions at air-water interfaces and can provide highly hydrophobic surface coatings. Although molecular simulations combined with experiments are promising for uncovering these mechanisms, the reliability of simulation results depends strongly on the accuracy of the force fields implemented. At the moment, atomistic force fields are not available to describe PFAS in a variety of environments. Ab initio methods could help fill this knowledge gap, but they are computationally demanding. As an alternative, ab initio calculations could be used to develop accurate force fields for atomistic simulations. In this work, a new algorithm is proposed, which, built from accurate ab initio calculations, yields force fields for perfluorinated sulfonic and perfluoroalkyl acids. The accuracy of the new force field was benchmarked against solvation free energy and interfacial tension data. The new force fields were then used to probe the interfacial behavior of the PFAS surfactants. The interfacial properties observed in our simulations were compared with those manifested by two branched fluorine-free surfactants. The good agreement achieved with experiments and ab initio calculations suggests that the proposed protocol could be implemented to study other perfluorinated substances and help in the design of fluorine-free surfactants for targeted applications.

Groundwater solutes influence the adsorption of short-chain perfluoroalkyl acids (PFAA) to colloidal activated carbon and impact performance for in situ groundwater remediation

Subsurface injection of colloidal activated carbon (CAC) is an in situ remediation strategy for perfluoroalkyl acids (PFAA), but the influence of groundwater solutes on longevity is uncertain, particularly for short-chain PFAA. We quantify the impact of inorganic anions, dissolved organic matter (DOM), and stabilizing polymer on PFAA adsorption to a commercial CAC. Surface characterization supported PFAA chain-length dependent adsorption results and mechanisms are provided. Inorganic anions decreased adsorption for short-chain PFAA (<7 perfluorinated carbons) due to competitive effects, while long-chain PFAA (≥ 7 perfluorinated carbons) were less impacted. DOM decreased adsorption of all PFAA in a chain-length dependent manner. High DOM concentrations (10 mg/L, ∼5 mg OC/L) decreased PFOA adsorption by a factor of 2, PFPeA by one order of magnitude, and completely hindered PFBA adsorption. High MW DOM has less impact on short-chain PFAA than low MW DOM, possibly due to differences in the ability to access CAC micropores. Low DOM concentrations (1 mg/L, ∼0.5 mg OC/L) did not impact adsorption. CMC (90 kDa average MW) had negligible impact on PFAA adsorption likely due to minimal CAC surface coverage. Longevity modeling demonstrated that groundwater solutes limit the capacity for PFAA in a CAC barrier, particularly for short-chain PFAA.

Regeneration of exhausted adsorbents after PFAS adsorption: A critical review

The adsorption process efficiently removes per- and polyfluoroalkyl substances (PFAS) from water, but managing exhausted adsorbents presents notable environmental and economic challenges. Conventional disposal methods, such as incineration, may reintroduce PFAS into the environment. Therefore, advanced regeneration techniques are imperative to prevent leaching during disposal and enhance sustainability and cost-effectiveness. This review critically evaluates thermal and chemical regeneration approaches for PFAS-laden adsorbents, elucidating their operational mechanisms, the influence of water quality parameters, and their inherent advantages and limitations. Thermal regeneration achieves notable desorption efficiencies, reaching up to 99% for activated carbon. However, it requires significant energy input and risks compromising the adsorbent's structural integrity, resulting in considerable mass loss (10-20%). In contrast, chemical regeneration presents a diverse efficiency landscape across different regenerants, including water, acidic/basic, salt, solvent, and multi-component solutions. Multi-component solutions demonstrate superior efficiency (>90%) compared to solvent-based solutions (12.50%), which, in turn, outperform salt (2.34%), acidic/basic (1.17%), and water (0.40%) regenerants. This hierarchical effectiveness underscores the nuanced nature of chemical regeneration, significantly influenced by factors such as regenerant composition, the molecular structure of PFAS, and the presence of organic co-contaminants. Exploring the conditional efficacy of thermal and chemical regeneration methods underscores the imperative of strategic selection based on specific types of PFAS and material properties. By emphasizing the limitations and potential of particular regeneration schemes and advocating for future research directions, such as exploring persulfate activation treatments, this review aims to catalyze the development of more effective regeneration processes. The ultimate goal is to ensure water quality and public health protection through environmentally sound solutions for PFAS remediation efforts.

Rim-Based Binding of Perfluorinated Acids to Pillararenes Purifies Water

Per- and polyfluoroalkyl substances (PFAS) pose a rapidly increasing global problem as their widespread use and high stability lead worldwide to water contamination, with significant detrimental health effects.[1] Supramolecular chemistry has been invoked to develop materials geared towards the specific capture of PFAS from water,[2] to reduce the concentration below advisory safety limits (e.g., 70 ng/L for the sum of perfluorooctane sulfonic acid, PFOS and perfluorooctanoic acid, PFOA). Scale-up and use in natural waters with high PFAS concentrations has hitherto posed a problem. Here we report a new type of host-guest interaction between deca-ammonium-functionalized pillar[5]arenes (DAF-P5s) and perfluoroalkyl acids. DAF-P5 complexes show an unprecedented 1 : 10 stoichiometry, as confirmed by isothermal calorimetry and X-ray crystallographic studies, and high binding constants (up to 106 M-1) to various polyfluoroalkyl acids. In addition, non-fluorinated acids do not hamper this process significantly. Immobilization of DAF-P5s allows a simple single-time filtration of PFAS-contaminated water to reduce the PFOS/PFOA concentration 106 times to 15-50 ng/L level. The effective and fast (<5 min) orthogonal binding to organic molecules without involvement of fluorinated supramolecular hosts, high breakthrough capacity (90 mg/g), and robust performance (>10 regeneration cycles without decrease in performance) set a new benchmark in PFAS-absorbing materials.

Pore size distribution and Al oxide content significantly regulated the effects of humic acid on perfluorooctanoic acid transport in natural soils

The ubiquity of dissolved organic matter (DOM) makes it encounter the released perfluorooctanoic acid (PFOA) in subsurface environment. However, the effect of DOM (e.g., humic acid, HA) on PFOA transport in soils and the critical influencing factors and mechanisms remain obscure. Column experiments were conducted to explore PFOA transport with the presence of different concentrations of HA in three types of soils and two types of Al oxide coated sand. Results revealed soil properties significantly regulate the effects of HA on PFOA transport, for which pore size distribution, minerals content (e.g., Al oxide) and pH were critical influencing soil-properties. For soil with large mesopore volume, pore blockage caused by HA controlled the effect of HA on PFOA transport. Large mesopore volume significantly alleviated pore blockage of HA, and led to insignificant effects of HA on PFOA transport. For soil exhibited minimum mesopore volume, Al oxide content and pH dominated the effect of HA on PFOA transport. Results from Al oxide coated sand (low mesopore volume) columns further proved that higher Al oxide content and lower pH caused more significant facilitating effect of HA on PFOA transport via site competition. Results highlighted the importance of considering pore size distribution and Al oxide content when assessing PFOA mobility capacity with co-transport with DOM in soils.

Removal of perfluoroalkyl acids from aqueous media by surfactant-modified clinoptilolites

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are environmentally persistent, bioaccumulating, and toxic compounds that have attracted global attention. It is challenging to reduce the residual concentrations of these compounds to safe discharge limits. In this study, batch experiments were performed to evaluate natural clinoptilolite and clinoptilolites modified (MC) with cetylpyridinium chloride (CPC-MC), didodecyldimethylammonium bromide (DDAB-MC), hexadecyltrimethylammonium bromide (HDTMA-MC), and tetramethylammonium chloride (TMA-MC) as cost-effective aqueous PFAS adsorbents. The removal capacities of the adsorbents for the majority of the PFASs decreased in the following order: DDAB-MC > CPC-MC ≫ modified natural clinoptilolite with hexadecyltrimethyl ammonium bromide (HDTMA-MC) ≫ modified natural clinoptilolite with tetramethylammonium chloride (TMA-MC) ≈ natural clinoptilolite modified with NaCl (NC). In particular, CPC-MC and DDAB-MC reduced PFASs concentration in 50 μg/L by up to 98% for perfluorooctane sulphonate. Within 30 min, CPC-MC (30.5 μg/L) and DDAB-MC (32.1 μg/L) met the PFOS water quality criterion of 36 μg/L in inland surface waters. Both adsorbents met this criterion at the highest solution volume (40 mL) and 0.125 g/L (solid-to-liquid ratio of 1:8). PFASs with short hydrocarbon chains competed more for adsorption. PFASs with sulphonate functional groups were also adsorbed more than carboxyl groups in single- and multi-PFAS solutions. The modified surfaces of clinoptilolites controlled PFAS adsorption through hydrophobic and electrostatic interactions. PFAS removal with surfactant-modified clinoptilolites is cost-effective and protects aquatic environments by using surplus natural materials.

Remediation of PFAS-impacted soils using magnetic activated carbon (MAC) and hydrothermal alkaline treatment (HALT)

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic pollutants that are bioaccumulative, toxic, and persistent. One long-term source for PFAS release is PFAS-contaminated soil. Addition of activated carbon (AC) to soil has shown the potential to immobilize PFAS and reduce PFAS bioavailability, but PFAS-loaded spent AC remaining in the treated soil could lead to remobilization. Here we report a novel approach to address this challenge. By applying magnetic activated carbon (MAC) to remediate PFAS-impacted soil, the PFAS-loaded MAC can be retrieved from the treated soil and sorbed PFAS in the spent MAC can be destroyed using hydrothermal alkaline treatment (HALT). Effective MAC recovery was observed when water/soil ratios (w/w) were either <0.07 or > 1. Soil organic content and pH affected PFAS adsorption by the MAC added to soil. After three months of incubation with MAC, high PFAS removals [PFOS (87.6 %), PFOA (83.8 %), and 6:2 FTSA (81.5 %)] were observed for acidic environmental sandy soils with low organic content. In contrast, PFAS removal by MAC was poor for garden soils with high organic matter content. MAC was also used to remediate aqueous film-forming foam (AFFF)-impacted and PFAS-contaminated aged soils with varying PFAS removal performance. HALT technology was able to destroy and defluorinate PFAS adsorbed to the spent MAC. Additionally, the HALT-treated MAC retained its magnetic properties and PFOS sorption capacity, suggesting the potential reusability of HALT-treated MAC. Considering the low energy footprint of HALT compared to conventional PFAS thermal destruction techniques, the combination of MAC and HALT could be a promising treatment train for PFAS-contaminated soils.

Physicochemical properties and interactions of perfluoroalkyl substances (PFAS) - Challenges and opportunities in sensing and remediation

Per- and polyfluoroalkyl substances (PFAS) is a class of persistent organic pollutants that presents health and environmental risks. PFAS are ubiquitously present in the environment, but current remediation technologies are ineffective in degrading them into innocuous chemicals, especially high energy degradation processes often generate toxic short chain intermediates. Therefore, the best remediation strategy is to first detect the source of pollution, followed by capturing and mineralising or recycling of the compounds. The main objective of this article is to summarise the unique physicochemical properties and to critically review the intermolecular and intramolecular physicochemical interactions of PFAS, and how these interactions can become obstacles; and at the same time, how they can be applied to the PFAS sensing, capturing, and recycling process. The physicochemical interactions of PFAS chemicals are being reviewed in this paper includes, (1) fluorophilic interactions, (2) hydrophobic interactions, (3) electrostatic interactions and cation bridging, (4) ionic exchange and (5) hydrogen bond. Moreover, all the different influential factors to these interactions have also been reported. Finally, properties of these interactions are compared against one another, and the recommendations for future designs of affinity materials for PFAS have been given.

Comparative study of per- and polyfluoroalkyl substances (PFAS) removal from landfill leachate

Landfill leachate is one of the major point sources of per- and polyfluoroalkyl substances (PFAS) pollution. In this study, powdered activated carbon (PAC), granular activated carbon (GAC), anion exchange resin (AIX), nanofiltration (NF), ozonation, and foam fractionation were tested for treatment of the same leachate. These methods were compared in terms of PFAS removal efficiencies and treatment cost. More than 75% removal of long-chain PFAS (6-9 CF2) could be achieved with all the studied methods, though with high resource consumption. It was demonstrated that PFAS breakthrough was up to 27 times faster when the leachate was treated with GAC and AIX compared to groundwater treatment. Nanofiltration was the only method which could be practically applied for removal of PFAS with the shortest fluorinated carbon chain (3-4 CF2). Foam fractionation and AIX offered the most economical treatment, with an estimated cost of < 1 €/m3 for PFOS and PFOA reduction to ≥ 90%. The cost of treatment was shown to increase exponentially if the goal of > 60% ΣPFAS11 removal was applied. It was also discussed that composite parameters that include expected toxicity of different PFAS, such as ΣPFOAeq, should be used to obtain a cost-efficient reduction of PFAS-induced water toxicity.

Revealing the factors resulting in incomplete recovery of perfluoroalkyl acids (PFAAs) when implementing the adsorbable and extractable organic fluorine methods

Per- and polyfluoroalkyl substances (PFASs) are environmental contaminants of concern. Techniques that quantify total organic fluorine (TOF) such as the adsorbable organic fluorine (AOF) and extractable organic fluorine (EOF) methods are important for PFAS risk assessments. The objective of this study was to systematically evaluate each step of the AOF (loading, washing, combustion) and EOF (loading, washing, elution, combustion) methods for the recovery of ten ultrashort-, short-, and long-chain unsubstituted perfluoroalkyl acids (PFAAs). We measured the overall recovery of fluoride for each method for each PFAA, and the recovery of each PFAA around the loading, washing, and elution steps. We also measured the combustion efficiency of each PFAA by direct combustion. The overall AOF and EOF recovery ranged from 9.3%-103.3% to 21.0%-108.1%, respectively, with higher recoveries measured for PFAAs with increasing chain length in both methods. The three ultrashort-chain PFAAs (trifluoroacetic acid, perfluoropropionic acid, and perfluoropropanesulfonic acid) exhibited the lowest overall recoveries from 9.3-25.2% for AOF and 21.0-51.5% for EOF. We found that decreases in the overall recovery are the result of losses of ultrashort- and short-chain PFAAs during the washing step and the incomplete mineralization of perfluoroalkyl sulfonic acids during combustion for AOF and incomplete elution of short- and long-chain PFAAs and the loss of ultrashort-chain PFAAs during the washing step for EOF. Our data suggest that the EOF method is more appropriate than the AOF method for measuring TOF in samples containing ultrashort- and short-chain PFAAs and that methodological improvements are possible with a focus on the washing, elution, and combustion steps.

Impact of Natural Organic Matter Competition on the Adsorptive Removal of Acetochlor and Metolachlor from Low-Specific UV Absorbance Surface Waters

Although activated carbon adsorption is a very promising process for the removal of organic compounds from surface waters, the removal performance for nonionic pesticides could be adversely affected by co-occurring natural organic matter. Natural organic matter can compete with pesticides during the adsorption process, and the size of natural organic matter affects the removal of pesticides, as low-molecular-weight organics directly compete for adsorbent sites with pesticides. This study aims to investigate the competitive impact of low-molecular-weight organics on the adsorptive removal of acetochlor and metolachlor by four commercial powdered activated carbons. The adsorption features of selected powdered activated carbons were evaluated in surface water samples collected from the influent stream of the filtration process having 2.75 mg/L organic matter and 0.87 L/mg-m specific UV absorbance. The adsorption kinetics and capacities were examined by employing pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models and modified Freundlich and Langmuir isotherm models to the experimental data. The competitive removal of acetochlor and metolachlor in the presence of natural organic matter was evaluated for varied powdered activated carbon dosages on the basis of UV and specific UV absorbance values of adsorbed organic matter. The adsorption data were well represented by the modified Freundlich isotherm, as well as pseudo-second-order kinetics. The maximum organic matter adsorption capacities of the modified Freundlich isotherm were observed to be 120.6 and 127.2 mg/g by Norit SX Ultra and 99.5 and 100.6 mg/g by AC Puriss for acetochlor- and metolachlor-containing water samples, respectively. Among the four powdered activated carbons, Norit SX Ultra and AC Puriss provided the highest natural organic matter removal performances with 76 and 72% and 71 and 65% for acetochlor- and metolachlor-containing samples, respectively. Similarly, Norit SX Ultra and AC Puriss were very effective for adsorbing aromatic organics with higher than 80% specific UV absorbance removal efficiency. Metolachlor was almost completely removed by higher than 98% by Norit SX Ultra, Norit SX F Cat, and AC Puriss, even at low adsorbent dosages. However, an adsorbent dose of 100 mg/L and above should be added for all powdered activated carbons, except for Norit SX F Cat, for achieving an acetochlor removal performance of higher than 98%. The competition between low-molecular-weight organics (low-specific UV absorbance) and acetochlor and metolachlor was more apparent at low adsorbent dosages (10-75 mg/L).

Factors Affecting the Adsorption of Per- and Polyfluoroalkyl Substances (PFAS) by Colloidal Activated Carbon

The immobilization of per- and polyfluoroalkyl substances (PFAS) by colloidal activated carbon (CAC) barriers has been proposed as a potential in-situ method to mitigate the transport of plumes of PFAS in the subsurface. However, if PFAS are continuously released from a source zone, the adsorptive sites on CAC will eventually become saturated, upon which point the breakthrough of PFAS in the barrier will occur. To predict the long-term effectiveness of CAC barriers, it is important to evaluate the factors that may affect the adsorption of PFAS on CAC. In this study, the adsorption of 7 PFAS on a polymer-stabilized CAC (i.e., PlumeStop®) and on a polymer-free CAC was investigated using batch experiments. The adsorption affinity of PFAS to CAC was in the following order: PFOS > 6:2 FTS > PFHxS > PFOA > PFBS > PFPeA > PFBA. This result indicates that hydrophobic interaction was the predominant adsorption mechanism, and that hydrophilic compounds such as PFBA and PFPeA will break through CAC barriers first. The partition coefficient Kd for the adsorption of PFAS on the polymer-stabilized CAC was 1.3 - 3.5 times smaller than the Kd for the adsorption of PFAS on the polymer-free CAC, suggesting that the polymers decreased the adsorption, presumably due to competitive sorption. Thus, the PFAS adsorption capacity of PlumeStop CAC barriers is expected to increase once the polymers are biodegraded and/or washed away. The affinity of PFOS and PFOA to CAC increased when the ionic strength of the solution increased from 1 to 100 mM, or when the concentration of Ca2+ increased from 0 to 2 mM. In contrast, less PFOS and PFOA were adsorbed in the presence of 1 - 20 mgC/L Suwannee River Fulvic Acid, which represented dissolved organic carbon, or in the presence of 10 - 100 mg/L diethylene glycol butyl ether (DGBE), which is an important component in some aqueous film-forming foam (AFFF) formulations. The presence of 0.5 - 4.8 mg/L benzene or 0.5 - 8 mg/L trichloroethylene, the co-contaminants that may comingle with PFAS at AFFF-impacted sites, diminished PFOS adsorption but had no effect or even slightly enhanced PFOA adsorption. When the initial concentration of TCE was 8 mg/L, the Kd (514 ± 240 L/g) for the adsorption of PFOS was approximately 20 times lower than that in the TCE-free system (Kd = 9,579 ± 829 L/g). The results of this study provided insights into some key factors that may affect the adsorption of PFAS in in-situ CAC barriers.

Sorption affinity and mechanisms of per-and polyfluoroalkyl substances (PFASs) with commercial sorbents: Implications for passive sampling

Effective monitoring tools, including passive samplers, are essential for the wide range of per- and polyfluoroalkyl substances (PFASs) in aquatic matrices. However, knowledge of the extent and mechanisms of PFASs sorption with sorbents in a passive sampling context is limited. To address this, sorption behavior of 45 anionic, neutral and zwitterionic PFASs ranging in perfluorocarbon chain length (C₃-C₁₆) and functional groups with 11 different commercial sorbents (cross-linked β-cyclodextrin polymers, activated carbon, anion exchange (AE), cation exchange, hydrophilic-lipophilic balanced (HLB) and non-polar) was investigated. A broad range of equilibrium sorbent-MilliQ water (MQ) distribution coefficients (K_d) were observed (10^-1.95 to 10^8.30 mL g^-1). Similar sorbent types (e.g., various AE and HLB sorbents) exhibited very different sorption behavior, likely due to their different polymeric structures and relative importance of sorbate/sorbent interactions other than coulombic interactions. HLB and AE with hydroxyl functionalities are most effective for sampling of the full suite of PFASs. Reduced sorptive affinity was observed in the presence of matrix co-constituents in wastewater influent for most PFASs. HLB had the smallest reduction in log K_d in wastewater suggesting that these sorbents are appropriate for applications in complex matrices. Sufficient sorbent capacity was observed for linear uptake of many target analytes which facilitates passive sampling.

Enhanced adsorption of short-chain perfluorobutanoic acid by functionalized periodic mesoporous organosilica: Performance and mechanisms

Removal of short-chain per- and polyfluoroalkyl substances (PFAS) represents a unique challenge in comparison to the long-chain homologs. In this study, a series of functionalized periodic mesoporous organosilica (PMO) materials with tunable molar ratio of fluoroalkyl to amine functional groups were developed and used as platform adsorbents to investigate the adsorption behavior of short-chain PFAS, with a focus on perfluorobutanoic acid (PFBA). Modification with fluoroalkyl group substantially enhanced the adsorption affinity of PFBA with the functionalized PMO materials. Adsorption free energy analysis suggested that although electrostatic interactions were more predominant in PFBA adsorption, modification of PMOs with increased fluoroalkyl group loadings increased the non-electrostatic interactions with PFBA, resulting in more favorable PFBA adsorption. The optimal functionalized PMO showed fast PFBA adsorption kinetics, excellent PFBA removal efficiency in various water chemistry conditions, and can be regenerated and reused for numerous cycles with methanol/water mixture containing 500-mM NH₃·H₂O as regenerant. Furthermore, the optimal functionalized PMO showed robust performance for the removal of PFAS mixtures under complex natural water matrix. Results of this study suggested the important role of non-electrostatic interactions in enhancing the removal of short-chain PFAS and can provide mechanistic insights into guiding the design of improved adsorbents for PFAS removal.

PFAS adsorbent selection: The role of adsorbent use rate, water quality, and cost

Per- and polyfluoroalkyl substance (PFAS) contamination in aqueous matrices has intensified the search for PFAS adsorbents with elevated capacity, selectivity, and cost effectiveness. A novel surface modified organoclay (SMC) adsorbent was evaluated for PFAS removal performance in parallel with granular activated carbon (GAC) and ion exchange resin (IX) for the treatment of five distinct PFAS impaired waters including groundwater, landfill leachate, membrane concentrate and wastewater effluent. Rapid small scale column tests (RSSCTs) and breakthrough modeling were coupled to provide insight on adsorbent performance and cost for multiple PFAS and water types. IX exhibited the best performance with respect to adsorbent use rates in treatment of all tested waters. IX was nearly four times more effective than GAC and two times more effective than SMC in the treatment of PFOA from water types excluding groundwater. Employed modeling strengthened the comparison of adsorbent performance and water quality to infer adsorption feasibility. Further, evaluation of adsorption was extended beyond PFAS breakthrough with the inclusion of unit adsorbent cost as a decision metric influencing adsorbent selection. An analysis of levelized media cost indicated treatment of landfill leachate and membrane concentrate was at least three times more expensive than groundwaters or wastewaters evaluated.

A review of PFAS adsorption from aqueous solutions: Current approaches, engineering applications, challenges, and opportunities

Per- and polyfluoroalkyl substances (PFAS) have drawn great attention due to their wide distribution in water bodies and toxicity to human beings. Adsorption is considered as an efficient treatment technique for meeting the increasingly stringent environmental and health standards for PFAS. This paper systematically reviewed the current approaches of PFAS adsorption using different adsorbents from drinking water as well as synthetic and real wastewater. Adsorbents with large mesopores and high specific surface area adsorb PFAS faster, their adsorption capacities are higher, and the adsorption process are usually more effective under low pH conditions. PFAS adsorption mechanisms mainly include electrostatic attraction, hydrophobic interaction, anion exchange, and ligand exchange. Various adsorbents show promising performances but challenges such as requirements of organic solvents in regeneration, low adsorption selectivity, and complicated adsorbent preparations should be addressed before large scale implementation. Moreover, the aid of decision-making tools including response surface methodology (RSM), techno-economic assessment (TEA), life cycle assessment (LCA), and multi criteria decision analysis (MCDA) were discussed for engineering applications. The use of these tools is highly recommended prior to scale-up to determine if the specific adsorption process is economically feasible and sustainable. This critical review presented insights into the most fundamental aspects of PFAS adsorption that would be helpful to the development of effective adsorbents for the removal of PFAS in future studies and provide opportunities for large-scale engineering applications.

Poly- and Perfluoroalkyl Substances (PFAS) in Landfills: Occurrence, Transformation and Treatment

Landfills have served as the final repository for > 50 % municipal solid wastes in the United States. Because of their widespread uses and persistence in the environment, per- and polyfluoroalkyl substances (PFAS) (>4000 on the global market) are ubiquitously present in everyday consumer, commercial and industrial products, and have been widely detected in both closed (tens ng/L) and active (thousands to ten thousands ng/L) landfills due to disposal of PFAS-containing materials. Along with the decomposition of wastes in-place, PFAS can be transformed and released from the wastes into leachate and landfill gas. Consequently, it is critical to understand the occurrence and transformation of PFAS in landfills and the effectiveness of landfills, as a disposal alternative, for long-term containment of PFAS. This article presents a state-of-the-art review on the occurrence and transformation of PFAS in landfills, and possible effect of PFAS on the integrity of modern liner systems. Based on the data published from 10 countries (250 + landfills), C4-C7 perfluoroalkyl carboxylic acids were found predominant in the untreated landfill leachate and neutral PFAS, primarily fluorotelomer alcohols, in landfill air. The effectiveness and limitations of the conventional leachate treatment technologies and emerging technologies were also evaluated to address PFAS released into the leachate. Among conventional technologies, reverse osmosis (RO) may achieve a high removal efficiency of 90-100 % based on full-scale data, which, however, is vulnerable to the organic fouling and requires additional disposal of the concentrate. Implications of these knowledge on PFAS management at landfills are discussed and major knowledge gaps are identified.

Adsorption of perfluoroalkyl acids on granular activated carbon supported chitosan: Role of nanobubbles

The safety threat posed by Perfluoroalkyl acids (PFAAs) in drinking water is a growing concern. In this study, we loaded chitosan (CS) on granular activated carbon (GAC) to adsorb PFAAs, and we explored the role of nanobubbles in the adsorption process through experiments and density functional theory (DFT) calculations. Compared with GAC, we found that the use of the composite adsorbent (CS/GAC) enhanced the removal rate of perfluorooctanoic acid by 136% with the assistance of nanobubbles. PFAAs with different chain lengths have different adsorption mechanisms owing to surface activity differences. PFAAs with longer C-F chains can be directly enriched with amino groups on the CS or air-water interface on composite adsorbents. Additionally, PFAAs can be enriched with nanobubbles in solution to form nanobubble-PFAA colloids, which are adsorbed by protonated amino groups on CS through electrostatic interactions. We found that PFAAs with shorter C-F chains are less affected by nanobubbles, and DFT calculations indicated that the adsorption of short-chain PFAAs is mainly affected by electrostatic interactions. We also proved that the electrostatic interactions between CS and PFAAs are mainly derived from the abundant protonated amino groups.

Removal of micropollutants using a membrane bioreactor coupled with powdered activated carbon - A statistical analysis approach

The occurrence of micropollutants in wastewater is largely documented as well as the environmental risk posed by their residues in the aquatic environment. Many investigations have been carried out and plan to study and improve their removal efficiency in existing wastewater treatment plants. At the same time, efforts are being made to develop new technologies or upgrade existing ones to increase the removal of a selection of micropollutants. Due to the great variability in their chemical and physical properties, it would be advisable to find representative compounds or identify the factors which most influence the removal mechanisms under specific conditions. This study analyses the removal efficiencies of a great number of micropollutants in wastewater treated in a membrane bioreactor coupled with powdered activated carbon (PAC), which was the subject of a review article we have recently published. The main operational parameters (i.e. PAC dosage, PAC retention time and sludge retention time) and compound physico-chemical properties (i.e. octanol-water distribution coefficient, charge and molecular weight) were first selected on the basis of a dedicated screening step and then an attempt was carried out to clarify their influence on the removal of micropollutants from wastewater during its treatment. To this end, a statistical analysis, mainly based on exploratory methods (cluster analysis and principal component analysis) and regression analysis, was carried out to compare and discuss the different results published in the scientific literature included in the cited review article. It emerged, that, based on the collected dataset, micropollutant charge and LogD_ow seem to play the most important role in the removal mechanisms occurring in MBR coupled with PAC.

Phytoremediation prospects of per- and polyfluoroalkyl substances: A review

Extensive use of per- and polyfluoroalkyl substances (PFASs) in various industrial activities and daily-life products has made them ubiquitous contaminants in soil and water. PFAS-contaminated soil acts as a long-term source of pollution to the adjacent surface water bodies, groundwater, soil microorganisms, and soil invertebrates. While several remediation strategies exist to eliminate PFASs from the soil, strong ionic interactions between charged groups on PFAS with soil constituents rendered these PFAS remediation technologies ineffective. Pilot and field-scale data from recent studies have shown a great potential of PFAS to bio-accumulate and distribute within plant compartments suggesting that phytoremediation could be a potential remediation technology to clean up PFAS contaminated soils. Even though several studies have been performed on the uptake and translocation of PFAS by different plant species, most of these studies are limited to agricultural crops and fruit species. In this review, the role of both aquatic and terrestrial plants in the phytoremediation of PFAS was discussed highlighting different mechanisms underlying the uptake of PFASs in the soil-plant and water-plant systems. This review further summarized a wide range of factors that influence the bioaccumulation and translocation of PFASs within plant compartments including both structural properties of PFASs and physiological properties of plant species. Even though phytoremediation appears to be a promising remediation technique, some limitations that reduced the feasibility of phytoremediation in the practical application have been emphasized in previous studies. Additional research directions are suggested, including advanced genetic engineering techniques and endophyte-assisted phytoremediation to upgrade the phytoremediation potential of plants for the successful removal of PFASs.

Examining sorption of perfluoroalkyl substances (PFAS) in biochars and other carbon-rich materials

The use of carbon-rich sorbents to remove and/or immobilize perfluoroalkyl substances (PFAS) in contaminated environmental scenarios is attracting increasing interest. The identification of key sorbent properties responsible for PFAS sorption and the development of models that can predict the distribution coefficients (K_d) for PFAS sorption in these materials are crucial in the screening of candidate materials for environmental remediation. In this study, sorption kinetics, sorption isotherms, and the effects of pH, calcium concentration and dissolved organic carbon (DOC) content on PFAS sorption were evaluated in four representative carbon-rich materials: two biochars with contrasting properties, a compost, and charcoal fines rejected by the metallurgical industry. Subsequently, the sorption of seven PFAS with numbers of fluorinated carbons ranging from 4 to 11 was evaluated in a total of ten carbon-rich materials, including activated carbons, so as to build up a K_d prediction model. The sorption of PFAS increased with greater fluorinated chain length, suggesting that hydrophobic interactions play a major role in sorption and electrostatic interactions a minor one. These results were confirmed by a principal component analysis, which revealed that the C_ORG/O molar ratio and the specific surface area of the material were the two main sorbent properties affecting PFAS sorption. Furthermore, the DOC content in solution had a negative effect on PFAS sorption. Using this information, a simple K_d prediction model applicable to a wide range of materials and PFAS was developed, using only a few easily-derived physicochemical properties of sorbent (C_ORG/O molar ratio and SSA) and PFAS (number of CF₂), and was externally validated with data gathered from the literature.

Removal of PFASs from water by carbon-based composite photocatalysis with adsorption and catalytic properties: A review

Per- and polyfluoroalkyl substances (PFASs) are a class of persistent organic pollutants widely distributed in aquatic environments. The adsorption and photocatalytic methods have been widely used to remove PFASs in water because of their respective advantages. Still, they have apparent defects when used alone. Therefore, the adsorption and photocatalytic technologies are combined through suitable preparation methods, and the excellent properties of the two are used to synergize the treatment of organic pollutants. This strategy of "concentrating" pollutants and then degrading them in a centralized manner plays an essential role in removing trace PFASs. Nevertheless, a review focusing on this kind of adsorption photocatalyst system is lacking. This review will fill this gap and provide a reference for developing a carbon-based composite photocatalyst. Firstly, different carbon-based composite photocatalysts are reviewed in detail, focusing on the differences in various composite materials' excellent adsorption and catalytic properties. Secondly, the factors influencing the removal effect of carbon-based composite photocatalysts are discussed. Thirdly, the removal mechanism of carbon-based composite photocatalysts is summarized in detail. The removal process involves two steps: adsorption and photodegradation. The adsorption process involves multiple cooperative adsorption mechanisms, and photocatalytic degradation includes oxidative and reductive degradation. Fourthly, the comparison of adsorption-photocatalysis with common treatment techniques (including removal rate, range of adaptation, cost, and the possibility of expanding application) is summarized. Finally, the prospects of carbon-based composite photocatalysts for repairing PFASs are given by evaluating the performance of different composites.

The role of dissolved organic matter during Per- and Polyfluorinated Substance (PFAS) adsorption, degradation, and plant uptake: A review

The negative effects of polyfluoroalkyl substances (PFAS) on the environment and health have recently attracted much attention. This article reviews the influence of soil- and water-derived dissolved organic matter (DOM) on the environmental fate of PFAS. In addition to being co-adsorped with PFAS to increase the adsorption capacity, DOM competes with PFAS for adsorption sites on the surface of the material, thereby reducing the removal rate of PFAS or increasing water solubility, which facilitates desorption of PFAS in the soil. It can quench some active species and inhibit the degradation of PFAS. In contrast, before DOM in water self-degrades, DOM has a greater promoting effect on the degradation of PFAS because DOM can complex with iron, iodine, among others, and act as an electron shuttle to enhance electron transfer. In soil aggregates, DOM can prevent microorganisms from being poisoned by direct exposure to PFAS. In addition, DOM increases the desorption of PFAS in plant root soil, affecting its bioavailability. In general, DOM plays a bidirectional role in adsorption, degradation, and plant uptake of PFAS, which depends on the types and functional groups of DOM. It is necessary to enhance the positive role of DOM in reducing the environmental risks posed by PFAS. In future, attention should be paid to the DOM-induced reduction of PFAS and development of a green and efficient continuous defluorination technology.

Adsorptive removal of propranolol under fixed-bed column using magnetic tyre char: Effects of wastewater effluent organic matter and ball milling

We investigated the competitive effects of different fractions of wastewater treatment plant effluent organic matter (EfOM) on adsorption of an organic micro pollutant (OMP), propranolol (PRO), in a fixed bed column packed with magnetic tyre char (MTC). The results showed that the presence of EfOM inhibited PRO adsorption in wastewater leading to decreased PRO adsorption capacity from 5.86 to 2.03 mg/g due to competitive effects and pore blockage by smaller EfOM fractions. Characterization of EfOM using size exclusion chromatography (LC-OCD) showed that the principal factor controlling EfOM adsorption was pore size distribution. Low molecular weight neutrals had the highest adsorption onto MTC while humic substances were the least interfering fraction. Effect of important parameters such as contact time, linear velocity and bed height/diameter ratio on MTC performance was studied in large-lab scale columns. Linear velocity and contact time were found to be effective in increasing adsorption capacity of PRO on MTC and delaying breakthrough time. Increase in linear velocity from 0.64 cm/min to 1.29 cm/min increased mass transfer and dispersion, resulting in considerable rise of adsorbed amount (5.86 mg/g to 22.58 mg/g) and increase in breakthrough time (15.8-62.7 h). Efficiency of non-equilibrium Hydrus model considering dispersion and mass transfer mechanism was demonstrated for real wastewater and scale up purposes. Ball milling for degradation of adsorbed PRO and regeneration of MTC resulted in 79% degradation of PRO was achieved after 5 h milling (550 rpm), while the addition of quartz sand increased the efficiency to 92%.

A dual grafted fluorinated hydrocarbon amine weak anion exchange resin polymer for adsorption of perfluorooctanoic acid from water

Perfluorooctanoic acid (PFOA) is a persistent and recalcitrant organic contaminant of exceptional environmental concern, and its removal from water has increasingly attracted global attention due to its wide distribution and strong bioaccumulation. Adsorption is considered an effective technique for PFOA removal and more efficient PFOA sorbents are still of interest. This study developed a dual grafted fluorinated hydrocarbon amine weak anion exchange (WAX) polymeric resin (Sepra-WAX-KelF-PEI) for PFOA removal from water. This polymer was synthesized by a two-step amine grafting reaction procedure involving first the reaction of the Sepra-WAX hydrocarbon polymer with poly(vinylidinefluoride-chlorotrifluoroethylene) (Kel-F 800) and then a second reaction with polyethyleneimine (PEI). Characterization of the synthesized polymers was performed using scanning electron microscopy and elemental analysis (F and Cl) by energy dispersive X-ray spectroscopy. The PFOA adsorption performance evaluations were conducted by packed column flow analyses with on-line detection. The results show the breakthrough of the Sepra-WAX-KelF-PEI synthesized with optimum stoichiometry was two times better than the starting anion exchange polymer Sepra-WAX, and six times better than powdered activated carbon, when using the same column size. The adsorption mechanisms of this novel adsorbent including hydrophobic interaction and electrostatic interaction were also clarified in this study. The adsorption kinetic parameters of the two optimum synthesized sorbents were determined using the Thomas model, the Yoon-Nelson model, and batch isotherm studies, and compared with those found with activated carbon and the starting WAX resin. Good agreement of the batch isotherm and column studies with respect to adsorption capacities trends between all three polymers (Sepra-WAX, Sepra-WAX-KelF, and Sepra-WAX-KelF-PEI) were noted.

Interactions between dissolved organic matter and perfluoroalkyl acids in natural rivers and lakes: A case study of the northwest of Taihu Lake Basin, China

Understanding the interactions between dissolved organic matter (DOM) and perfluoroalkyl acids (PFAAs) is essential for predicting the distribution, transport, and fate of PFAAs in aquatic environments. Based on field investigations in the northwest of Taihu Lake Basin combined with laboratory experiments, we obtained DOM and PFAA concentrations as well as compositions and investigated key factors of DOM affecting PFAA variability and capture of PFAAs by DOM. Results indicated that the total concentrations of PFAAs were 73.4-689 ng/L in surface water and that PFAAs were dominated by C3-7 perfluoroalkyl carboxylic acids and perfluorooctane sulfonic acid. The main components of DOM included tyrosine-, fulvic-, and tryptophan-like substances. The Mantel test revealed a significant positive correlation between DOM and PFAAs (P = 0.0001). Fulvic-like substances were identified as the most crucial factors affecting PFAA variability. The laboratory experiments revealed that DOM can spontaneously aggregate into a microgel. Furthermore, 19.1-50.9% of PFAAs, DOM characteristic peaks, and several metals (Ca, Mg, Cu, and Fe) can be removed during aggregation, indicating the capacity of DOM binding organic/inorganic substances. The fulvic-like substances were more effectively removed than the protein-like substances. The distribution coefficients of all PFAAs except perfluorohexanoic acid significantly correlated with their perfluorinated carbon numbers (r = 0.975, p<0.001). Our results provided insights into the interactions between DOM and PFAAs, improving the understanding of the distribution, transport, and fate of PFAAs in aquatic environments.

A review on per- and polyfluorinated alkyl substances (PFASs) in microplastic and food-contact materials

Plastic, paper and cardboard are widely used as food contact materials (FCMs), due to its numerous favourable characteristics. However, they are usually coated with hazardous substances, such as per- and polyfluorinated alkyl substances (PFASs). PFASs, with its functional properties of oil- and water-repellency, can migrate from FCMs into the food and cause potential risk to human health. There are also increasing concerns about the harm that FCMs can cause to the environment. These concerns include accumulation of non-degradable plastics in the environment, generation of microplastics (MPs) and nanoplastics, and release of PFASs from FCMs. While many reviews have been conducted on PFASs in the environment, including their occurrence, fate, toxicity, biodegradation, migration in ecosystems and remediation technologies, a systematic review of PFASs in FCMs and MPs is currently lacking. In addition, our knowledge of the PFAS sorption processes on MPs is rather limited, and in particular their desorption processes. Thus, this review aims to (1) review the presence of various classes of PFASs in FCMs and their migration into food, (2) review the PFASs in MPs and summarize the sorption mechanisms, and factors that influence their sorption behaviour on MPs in the aquatic environment, and (3) identify the current research gaps and future research directions to predict the risks associated with the presence and sorption of PFASs in FCMs and MPs.

Rapid removal of PFOA and PFOS via modified industrial solid waste: Mechanisms and influences of water matrices

Emerging perfluoroalkyl and polyfluoroalkyl substances contaminate waters at trace concentrations, thus rapid and selective adsorbents are pivotal to mitigate the consequent energy-intensive and time-consuming issues in remediation. In this study, coal combustion residuals-fly ash was modified (FA-SCA) to overcome the universal trade-off between high adsorption capacity and fast kinetics. FA-SCA presented rapid adsorption (t_eq = 2 min) of PFOX (perfluorooctanoic acid and perfluorooctanesulfonic acid, collectively), where the dynamic adsorption capacity (q_dyn = q_m/t_eq) was 2-3 orders of magnitude higher than that of benchmark activated carbons and anion-exchange resins. Investigated by advanced characterization and kinetic models, the fast kinetics and superior q_dyn are attributed to (1) elevated external diffusion driven by the submicron particle size; (2) enhanced intraparticle diffusion caused by the developed mesoporous structure (V_meso/V_micro = 8.1); (3) numerous quaternary ammonium anion-exchange sites (840 μmol/g), and (4) appropriate adsorption affinity (0.031 L/μmol for PFOS, and 0.023 L/μmol for PFOA). Since the adsorption was proven to be a synergistic process of electrostatic and hydrophobic interactions, effective adsorption ([PFOX]_ini = 1.21 μM, concentration levels of highly-contaminant-sites) was obtained at conventional natural water chemistries. High selectivity (>85.4% removal) was also achieved with organic/inorganic competitors, especially compounds with partly similar molecular structures to PFOX. In addition, >90% PFOX was removed consistently during five cycles in mild regeneration conditions (pH 12 and 50 °C). Overall, FA-SCA showed no leaching issues of toxic metals and exhibits great potential in both single-adsorption processes and treatment train systems.

Novel Fluorinated Nitrogen-Rich Porous Organic Polymer for Efficient Removal of Perfluorooctanoic Acid from Water

The mobility, durability, and widespread use of perfluorinated and polyfluoroalkyl substances (PFAS), notably perfluorooctanoic acid (PFOA), bring about serious contamination of many ground and surface waters. In this study, fluorine and amine-functionalized porous organic polymer (POP-4F) was designed and successfully synthesized as an adsorbent for PFOA removal in water. The characterization results showed that the synthesized material had an amorphous microporous structure, and the BET surface area was up to 479 m2 g−1. Its versatile adsorption property was evaluated by batch adsorption experiments using PFOA as a probe. The experiments show that the polymer was able to remove 98% of the PFOA in 5 min from water and then desorb within 3 min in methanol ([PFOA]0 = 1 mg L−1; [POP-4F] = 200 mg L−1). Specifically, the adsorption capacity of POP-4F is up to 107 mg g−1, according to the Langmuir fit. The rapid adsorption and desorption of PFOA by POP-4F offers the possibility of economical, environmentally friendly, and efficient treatment of real wastewater.

Activated carbon versus metal-organic frameworks: A review of their PFAS adsorption performance

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of fluorinated aliphatic compounds considered as emerging persistent pollutants. Owing to their adverse effects on human health and environment, efficient methods of their removal from various complex matrices need to be developed. This review focuses on recent results addressing the adsorption of PFAS on activated carbons (AC) and metal-organic frameworks (MOF). While the former are well-established adsorbents used in water treatment, the latter are relatively new and still not applied at a large scale. Nevertheless, they attract research interests owing to their developed porosity and versatile surface chemistry. While AC provide high volumes of pores and hydrophobic surfaces to strongly attract fluorinated chains, MOF supply sites for acid-base complexation and a variety of specific interactions. The modifications of AC are focused on the introduction of basicity to attract PFAS anions via electrostatic/chemical interactions, and those of MOF - on structural defects to increase the pore sizes. Based on the comparison of the performance and specifically adsorption forces provided by these two groups of materials, activated carbons were pointed out as worthy of further research efforts. This is because their surface, especially that in large pores, where dispersive forces are week and where extensive pore space might be utilized to adsorb more PFAS, can be further chemically modified and these modifications might be informed by the mechanisms of PFAS adsorption, which are specific for MOF. This review emphasizes the effects of these modifications on the adsorption mechanism and brings the critical assessment of the advantages/disadvantages of both groups as PFAS adsorbents.

Biochar sorption of perfluoroalkyl substances (PFASs) in aqueous film-forming foams-impacted groundwater: Effects of PFASs properties and groundwater chemistry

The widespread use of per- and polyfluoroalkyl substances (PFASs)-related products such as aqueous film-forming foams (AFFF) has led to increasing contamination of groundwater systems. The concentration of PFASs in AFFF-impacted groundwater can be several orders of magnitude higher than the drinking water standard. There is a need for a sustainable and effective sorbent to remove PFASs from groundwater. This work aims to investigate the sorption of PFASs in groundwater by biochar column. The specific objectives are to understand the influences of PFASs properties and groundwater chemistry to PFASs sorption by biochar. The PFASs-spiked Milli-Q water (including 19 PFASs) and four aqueous film-forming foams (AFFF)-impacted groundwater were used. The partitioning coefficients (log K_d) of long chain PFASs ranged from 0.77 to 4.63 while for short chain PFASs they remained below 0.68. For long chain PFASs (C ≥ 7), log K_d increased by 0.5 and 0.8 for each CF₂ moiety of PFCAs and PFSAs, respectively. Dissolved organic matter (DOM) was the most influential factor in PFASs sorption over pH, salinity, and specific ultraviolet absorbance (SUVA). DOM contained hydrophobic compounds and metal ions which can form DOM-PFASs complexes to provide more sorption sites for PFASs. The finding is useful for executing PFASs remediation by biochar filtration column, especially legacy long chain PFASs, for groundwater remediation.

Comparison of Zn-Al and Mg-Al layered double hydroxides for adsorption of perfluorooctanoic acid

Per-and polyfluoroalkyl substances (PFAS), a large class of synthesized chemicals, are persistent in nature and generally recalcitrant to conventional chemical and biological treatment. Adsorption is considered an economical and practical method for PFAS treatment. Layered double hydroxides (LDHs) represent a promising class of mineral-based adsorbents for PFAS removal because of the highly positive charge of their structural layers. In this research, the performance of two representative LDHs with varied cation compositions, namely Zn-Al and Mg-Al LDHs, were investigated and compared for the removal of perfluorinated carboxylic acids (PFCAs) with an emphasis on perfluorooctanoic acid (PFOA). Zn-Al LDH showed high efficiency for the removal of medium- and long-chain PFCAs (i.e., C ≥ 7), and performed consistently better than Mg-Al LDH. Based on detailed adsorption kinetics and isotherm studies toward PFOA, Zn-Al LDH showed higher adsorption capacity, stronger adsorption affinity, and faster kinetics than Mg-Al LDH. Presence of natural organic matter had minimal impact on PFOA removal by Zn-Al LDH, but sulfate severely inhibited PFOA adsorption. Combined results of aqueous adsorption experiments and sorbent characterization suggested that electrostatic interactions may be the primary mechanism for PFOA adsorption onto LDHs. Our results suggested that cation composition of LDHs can have significant effect on the performance for PFCA removal.

Per- and poly-fluoroalkyl substance remediation from soil and sorbents: A review of adsorption behaviour and ultrasonic treatment

Per- and poly-fluoroalkyl substances (PFAS) are xenobiotics, present at variable concentrations in soils and groundwater worldwide. Some of the current remediation techniques being researched or applied for PFAS-impacted soils involve solidification-stabilisation, soil washing, excavation and disposal to landfill, on site or in situ smouldering, thermal desorption, ball milling and incineration. Given the large volumes of soil requiring treatment, there is a need for a more environmentally friendly technique to remove and treat PFASs from soils. Sorbents such as granular/powdered activated carbon, ion exchange resins and silicas are used in water treatment to remove PFAS. In this work, PFAS adsorption mechanisms and the effect of pore size, pH and organic matter on adsorption efficacy are discussed. Then, adsorption of PFAS to soils and sorbents is considered when assessing the viability of remediation techniques. Sonication-aided treatment was predicted to be an effective removal technique for PFAS from a solid phase, and the effect of varying frequency, power and particle size on the effectiveness of the desorption process is discussed. Causes and mitigation strategies for possible cavitation-induced particle erosion during ultrasound washing are also identified. Following soil remediation, degrading the extracted PFAS using sonolysis in a water-organic solvent mixture is discussed. The implications for future soil remediation and sorbent regeneration based on the findings in this study are given.

GenX is not always a better fluorinated organic compound than PFOA: A critical review on aqueous phase treatability by adsorption and its associated cost

Hexafluoropropylene oxide dimer acid (GenX) has been marketed as a substitute for perfluorooctanoic acid (PFOA) to reduce environmental and health risks. GenX and PFOA have been detected in various natural water sources, and adsorption is recognized as a typical treatment process for PFOA removal. In this paper, comparisons of GenX and PFOA adsorption are evaluated, including adsorption potential, adsorption mechanisms, and associated costs. A detailed literature review suggests that anion-exchange resins are more effective in removing GenX than activated carbon. GenX removal efficiency through activated carbon (30%) is lower than that of PFOA (80-95%), while GenX and PFOA removal efficiencies by anion exchange resins are similar (99%). Unconventional adsorbents, such as ionic fluorogels and covalent organic frameworks can effectively remove GenX from water. The review reveals that GenX adsorption is more challenging, requiring almost 4 times the treatment cost of its predecessor, PFOA. Annual operation and maintenance costs for GenX adsorption (initial concentration of GenX and PFOA = 0.2 µg.L^-1) by GAC for treating 10,000 m³ per day is almost US$1,000,000 per year, but only around US$240,000 per year for PFOA. Desorption of GenX in the presence of PFOA highlights GenX's inferior treatability by adsorption. It is believed that GenX is a more environmentally friendly compound than PFOA, but this environmental friendliness comes with the price.

What is specific in adsorption of perfluoroalkyl acids on carbon materials?

Various activated carbon products show wide variability in adsorption performance towards perfluoroalkyl acids (PFAAs) and predictive tools are largely missing. In order to gain a better understanding on the adsorption mechanisms of PFAAs, perfluorooctanoic acid (PFOA) was compared with its fluorine-free analogon octanoic acid (OCA) as well as phenanthrene (nonionic) in terms of their response towards changes in carbon surface chemistry. For this approach, a commercial activated carbon felt (ACF) with high content of acidic surface groups was modified by amino-functionalisation as well as thermal defunctionalisation in H₂ (yielding DeCACF). While improvement by amino-functionalisation was moderate, defunctionalisation drastically enhanced adsorption of PFOA and other PFAAs. In comparison, OCA and phenanthrene were much less affected. Electrostatic interactions and charge compensation provided by positively charged surface sites (quantified by their anion exchange capacity) are obviously more crucial for PFAAs than for common organic acids (such as the tested OCA). A possible reason is their exceptionally strong acidity with pK_a < 1. Nevertheless, at the best modified ACF material (DeCACF) the sorption coefficients (K_d) for PFOA and perfluorooctylsulfonic acid (PFOS) at environmentally relevant concentrations reach the range of 10⁷ L/kg which is outstanding. DeCACF provides a surface with overall low polarity (low O-content), low density of acidic sites causing electrostatic repulsion, but nevertheless a sufficient density of charge-balancing sites for organic anions. The results of the present study contribute to an optimized selection of adsorbents for PFAA adsorption from water considering also various salt matrices and the presence of natural organic matter.

Effect of soil organic matter on the plant uptake of perfluorooctanoic acid (PFOA) and perfluorooctanesulphonic acid (PFOS) in lettuce on granular activated carbon-applied soil

The presence of perfluorooctanoic acid (PFOA) and perfluorooctanesulphonic acid (PFOS) in crops is an important consideration for food safety. The soil organic matter (SOM) content may affect the adsorption potential of PFOA and PFOS in water and soil and their subsequent uptake in crops. To better understand these dynamics, the adsorption and uptake of PFOA and PFOS in lettuce were investigated using granular activated carbon (GAC)-treated soils with varying SOM content. The adsorption potential of GAC was investigated, with maximum adsorption capacities for PFOA and PFOS calculated to be 9.091 mg g-1 and 27.778 mg g-1, respectively. These values decreased to 5.208 mg g-1 and 17.241 mg g-1, respectively, after the addition of 0.04 wt% humic acid. The average plant uptake factor (PUF) in low and high perfluoroalkyl and polyfluoroalkyl acid (PFAA)-contaminated soils with 4.0 wt% SOM was restricted to 0.353 for PFOA and 0.108 for PFOS. The PUFs were approximately two times lower than those for soil with 2.6 wt% SOM. Addition of 1 wt% GAC to the soil successfully reduced the PUF by up to 99.4%, with values of 0.006 (PFOA) and 0.005 (PFOS) in 2.6 wt% SOM-treated soil and 0.079 (PFOA) and 0.023 (PFOS) in 4.0 wt% SOM-treated soil. Although the PUF in the GAC-treated soil was drastically decreased, the PUF of the soil with 4.0 wt% SOM was at least four times higher than that with 2.6 wt% SOM. Therefore, SOM content is an important consideration in the remediation of PFOA- and PFOS-contaminated farmland soil using carbonaceous adsorbent.