Perfluoroalkyl Acids Removal Research Articles

Removal of perfluoroalkyl acids and precursors with silylated clay: Efficient adsorption and enhanced reuse

Organically modified clays (organoclays) have been considered effective adsorbents for the treatment of per- and polyfluoroalkyl substances (PFAS). However, the stability of organoclays prepared through the conventional cation exchange approach has been a major concern for their practical application. In this study, we reported the development of a new organically functionalized clay by grafting pillared clay substrate with an organosilane through covalent bonding. The performance of the silylated clay (QAG-ZrMT) was systematically compared with an organoclay prepared from ion exchange (HDTMA-ZrMT) for the adsorption of two legacy perfluoroalkyl acids: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), and two precursor compounds 5:3 fluorotelomer carboxylic acid (5:3FTCA) and 6:2 fluorotelomer sulfonic acid (6:2FTS). Compared to HDTMA-ZrMT, QAG-ZrMT showed substantially improved performance for adsorption of less hydrophobic PFAS (e.g., 5:3FTCA), which could be related to the stronger electrostatic interactions between PFAS and QAG-ZrMT than HDTMA-ZrMT. More importantly, QAG-ZrMT could be conveniently regenerated and reused for multiple cycles with robust performance. In contrast, HDTMA-ZrMT almost completely lost its capacity for PFAS removal after regeneration, due to the loss of organic functional groups during solvent regeneration. Results can shed light on the design of efficient and regenerable organoclay adsorbents for remediation of PFAS-contaminated water matrices.

Can on-site leachate treatment facilities effectively address the issue of perfluoroalkyl acids (PFAAs) in leachate?

In recent decades, the presence of perfluoroalkyl acids (PFAAs) in municipal solid waste leachate has emerged as a growing concern. Research has focused on PFAA release and occurrence characteristics in landfill and waste-to-energy leachate, highlighting their significant impact when released into wastewater treatment plants. Given the extremely high loading rate faced by current on-site leachate treatment plants (LTPs), the objective of this study is to assess whether the current “anaerobic/aerobic (A/O) + membrane bioreactor (MBR) + nanofiltration (NF) + reverse osmosis (RO)” configuration is effective in PFAAs removal. Concentrations of raw and treated leachate in 10 on-site LTPs with same treatment configuration and varying landfill ages were measured, and a comprehensive mass flow analysis of each treatment process was conducted. The results indicate that A/O treatment has limited capacity for PFAA removal, while NF and RO processes reached 77.44 % and 94.30 % removal rates of ∑PFAAs concentration, respectively. Short-chain PFAAs (> 80 % detected frequency) primarily influenced the distribution and variations of PFAAs in leachate and tend to disperse in the water phase. Correlation analysis revealed the current on-site LTPs exhibit a more efficient removal capacity for long-chain PFAAs.

Removal of perfluoroalkyl acids (PFAAs) from aqueous solution by water hyacinth (Eichhornia crassipes): Uptake, accumulation, and translocation

Although Eichhornia crassipes, commonly known as water hyacinth, has been widely used in wastewater treatment, further investigations are still needed to explore the removal efficiency of perfluoroalkyl acids (PFAAs) from the aqueous environment using this floating aquatic plant. In this study, a hydroponic experiment was conducted to assess accumulation, bioconcentration factors (BCFs), translocation factors (TFs), and removal rates of eight PFAAs by water hyacinth. The obtained results indicated that all PFAAs, including five perfluoroalkyl carboxylic acids (PFCAs) with chain lengths C4-C8 and three perfluoroalkyl sulfonic acids (PFSAs) with C4, C6, and C8, were readily accumulated in water hyacinth. Throughout the duration of the experiment, there was a noticeable increase in PFAA concentrations and BCF values for different plant parts. For the root, PFAAs with more carbon numbers showed a higher uptake than the shorter homologues, with PFSAs being more readily accumulated compared to PFCAs with the same carbon number in the molecules. In contrast, the levels of long-chain PFAAs were comparatively lower than those of short-chain substances in the stem and leaf. Notably, PFAAs with less carbon numbers, like PFPeA, PFBA, and PFBS, showed a remarkable translocation from the root to the stem and leaf with TFs >1. For the whole plant, no significant correlation was found between BCFs and organic carbon-water partition coefficients (Koc), octanol-water partition coefficients (Kow), membrane-water distribution coefficients (Dmw), or protein-water distribution coefficients (Dpw). The removal rates of PFAAs ranged from 40.3 to 63.5 % throughout the three weeks of the experiment while the removal efficiencies varied from 48.9 % for PFHxS to 82.6 % for PFPeA in the last week.

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 50μg/L by up to 98% for perfluorooctane sulphonate. Within 30min, CPC-MC (30.5μg/L) and DDAB-MC (32.1μg/L) met the PFOS water quality criterion of 36μg/L in inland surface waters. Both adsorbents met this criterion at the highest solution volume (40mL) and 0.125g/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.

Synthesis of Olefin-Linked high stability covalent organic frameworks for the removal of perfluoroalkyl acids from water

Covalent organic frameworks (COFs) are promising adsorbents due to their designable functionality, but their applications are hampered by poor chemical stability. Herein, a series of novel high stability olefin-linked (C = C) COFs with different ratios of OMe, as the adsorbent to remove perfluoroalkyl acids (PFAAs), were firstly synthesized by a three-component strategy under solvothermal conditions. The synthesized COFs showed strong resistance toward acid (6 M HCl) and base (6 M NaOH) because of the robust C = C linkage which can be achieved reversibly under stringent synthetic conditions. Among the four [OMe]x-COF adsorbents, [OMe]100-COF exhibited the highest adsorption affinities and adsorption capacities for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). The theoretical maximum adsorption capacity of [OMe]100-COF for PFOA and PFOS, calculated by Langmuir isotherm, were 601.2 mg g−1 and 1106.1 mg g−1, respectively. This could be ascribed to the synergistic combination of electrostatic interaction and hydrophobic-hydrophobic interaction. Moreover, [OMe]100-COF can be efficiently regenerated during the adsorption–desorption cycles. This study provides a novel strategy to fabricate olefin-linked COFs for the effective adsorption of perfluorinated compounds in water. Environmental implicationPerfluorinated compounds (PFAAs) were shortlisted for persistent organic pollutants (POPs) in 2009 due to their persistence, bioaccumulation, toxicity, and long-distance mobility. Adsorption is one of the promising ways with advantages of simplicity and low energy consumption for removing PFAAs from aqueous environment. Herein, a series of olefin-linked COFs with high chemical stability was synthesized using a three-component strategy. And they showed rapid uptake and high capacity for the removal of PFAAs. This study provides a novel strategy to fabricate olefin-linked COFs for the effective adsorption of perfluorinated compounds in water.

Impact of effluent organic matter on perfluoroalkyl acid removal from wastewater effluent by granular activated carbon and alternative adsorbents

Occurrence of perfluoroalkyl acids (PFAAs) in wastewater effluent coupled with increasingly stringent regulations has increased the need for more effective sorption-based PFAA treatment approaches. This study investigated the impact of ozone (O3)- biologically active filtration (BAF) as integral components of non-reverse osmosis (RO)-based potable reuse treatment trains and as a potential pretreatment option to improve adsorptive PFAA removal from wastewater effluent by nonselective (e.g., granular activated carbon (GAC) and selective (e.g., anionic exchange resins (AER) and surface-modified clay (SMC)) adsorbents. For nonselective GAC, O3 and BAF resulted in similar PFAA removal improvements, while BAF alone performed better than O3 for AER and SMC. O3-BAF in tandem resulted in the highest PFAA removal performance improvement among pretreatments investigated for selective and nonselective adsorbents. Side by side evaluation of the dissolved organic carbon (DOC) breakthrough curves and size exclusion chromatography (SEC) for each pretreatment scenario suggested that despite the higher affinity of selective adsorbents towards PFAAs, the competition between PFAA and effluent organic matter (EfOM) (molecular weights (MWs): 100–1000 Da) negatively impacts the performance of these adsorbents. The SEC results also demonstrated that transformation of hydrophobic EfOM to more hydrophilic molecules during O3 and biotransformation of EfOM during BAF were the dominant mechanisms responsible for alleviating the competition between PFAA and EfOM, resulting in PFAA removal improvement.

The addition of iron-carbon enhances the removal of perfluoroalkyl acids (PFAAs) in constructed wetlands

Hazardous perfluoroalkyl acids (PFAAs), particularly perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), have become ubiquitous environmental persistent organic contaminants, posing serious threats to environmental health, which has led to the development of PFAA treatment methods. Wetland construction in combination with iron-carbon (CW–I), a low-maintenance and high-efficiency technology, may be capable of removing PFAAs through physico-biochemical processes. In this study, we aim to investigate the removal efficiency of PFAAs by CW-I as well as the critical functions of all components within the wetlands. Pairwise comparisons of iron-carbon and control groups revealed that iron-carbon significantly enhanced 15.9% for PFOA and 17.9% for PFOS absorption through phytouptake and substrate adsorption, with respective removal efficiencies of 71.8% ± 1.03% and 85.8% ± 1.56%. The generated iron ions stimulated plant growth and further enhanced phytouptake of PFAAs, with PFAAs accumulated primarily in root tissues with limited translocation. Observations of batch adsorption suggest that chemical and electrostatic interactions are involved in the iron-carbon adsorption process, with film and intraparticle diffusions being the rate-limiting events. Fourier transform infrared spectrometer and X-ray photoelectron spectroscopy revealed that PFAA adsorption by substrates occurs at the molecular level, as well as the occurrence of hydrophobic force effects and ligand exchanges during the iron-carbon adsorption process. Additionally, iron-carbon significantly altered the genera, phyla, and community structure of microorganisms, and some microorganisms and their extracellular polymers may possess ability to bind PFAAs. The information provided in this study contributes to our understanding of the PFAA removal processes in CW-I and enriched the classical cases of PFAA removal by CWs.

Evaluating the Performance of Novel Cyclodextrin Polymer Granules to Remove Perfluoroalkyl Acids (PFAAs) from Water

Cyclodextrin polymers (CDPs) are promising adsorbents for the removal of per- and polyfluoroalkyl substances (PFASs) from water. For CDPs to be implemented in packed-bed filtration (PBF) systems, CDP powders must be processed to produce CDP granules of a defined size. In this study, we introduce CDP granules with average particle diameters (dp) of 84–718 μm produced from a CDP powder by means of high-shear spray granulation. We evaluated the performance of the CDP granules in batch studies to evaluate the adsorption kinetics, capacity, and affinity for six perfluoroalkyl acids (PFAAs). We also performed rapid small-scale column test (RSSCT) experiments for three of the CDP granules (dp = 84, 175, 359 μm) to test whether the assumptions of constant diffusivity (CD) or proportional diffusivity (PD) are appropriate for these CDP granules. We found that CDP granules exhibit slower adsorption kinetics than the CDP powder (rate constants ranging between 0.2 and 2.7 g mg–1 h–1 for all PFAAs and all CDP granules), but that CDP granules of varying sizes exhibit relatively consistent adsorption kinetics. Adsorption capacity (139–479 μmol g–1) and affinity (0.6–149 L mg–1) were relatively constant across CDP granules of varying particle diameters for all PFAAs but adsorption capacity decreased and adsorption affinity increased for longer-chain PFAAs. Data from the RSSCT experiments suggest that neither the assumption of CD nor PD are unequivocally appropriate for CDP granules and that an improved understanding of mass transfer limitations as a function of particle size is essential. Overall, our results demonstrate the potential for novel CDP granules to be implemented in PBF systems for the removal of PFAAs from water.

Removal of perfluoroalkyl acids and common drinking water contaminants by weak-base anion exchange resins: Impacts of solution pH and resin properties

The underlying chemistry of weak-base (WB) anion exchange resins (AERs) for contaminant removal from water is not well documented in the literature. To address this, batch adsorption experiments were conducted at pH 4, 7, and 10 using two representative WB-AERs (polyacrylic IRA67 and polystyrene IRA96) and two representative strong-base (SB) AERs (polyacrylic IRA458 and polystyrene A520E), of differing polymer composition, for the removal of nitrate, sulfate, 3-phenylpropionic acid (3-PPA) as surrogate for natural organic matter, and six perfluoroalkyl acids (PFAAs). Under acidic (pH 4) and neutral (pH 7) conditions, the selectivity of AERs for each contaminant was predominantly influenced by polymer composition followed by the size of the resin functional group. This result reflected the WB-AERs being fully protonated and functioning identical to SB-AERs. Isotherm model parameters revealed WB-AER had higher capacity than SB-AER with analogous polymer composition and porosity regardless of resin selectivity for each contaminant. Under basic conditions (≥ pH 10), contaminant removal by WB-AERs declined due to deprotonation of the tertiary amine functional groups. Removal of PFAAs by the more hydrophobic polystyrene WB-AER (IRA96) remained approximately constant with changing pH, which was possibly due to electrostatic interactions with remaining protonated amine functional groups on the resin.

Impact of ozone-biologically active filtration on the breakthrough of Perfluoroalkyl acids during granular activated carbon treatment of municipal wastewater effluent

The presence of perfluoroalkyl acids (PFAAs) in municipal wastewater has highlighted the need to develop PFAA treatment approaches for wastewater effluent and potable reuse applications. Ozone (O3) and biologically active filtration (BAF) were investigated as standalone and combined pretreatment processes to improve the performance of granular activated carbon (GAC) for PFAA removal from wastewater effluent. As individual processes, ozonation at all three investigated doses (0.35, 0.75, 1.0 mg O3/mg DOC) and BAF at both tested empty bed contact times (EBCT; 15 and 20 min) led to significant improvement in PFAA removal by subsequent GAC treatment. With respect to standalone ozonation, the specific O3 dose of 0.75 mg O3/mg DOC was proven to be the optimum operating condition as further increase of the specific ozone dose to 1.0 mg O3/mg DOC did not provide considerable additional improvement. Extending the EBCT during standalone BAF from 15 to 20 minutes significantly improved the efficacy of GAC for the removal of tested PFAAs. Pretreatment with O3-BAF (0.75 mg O3/mg DOC; 20 min EBCT) in tandem outperformed both standalone ozonation and BAF for the removal of PFAA by GAC. Characterization of effluent organic matter (EfOM) by size exclusion chromatography (SEC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) before and after pretreatments suggest that among multiple co-occurring phenomena, the shift towards smaller and more polar EfOM may have predominantly alleviated pore constriction/blockage without having adverse impact on direct site competition. This observation is supported by SEC and FT-ICR-MS results indicating reduced EfOM molecular size through O3 and BAF pretreatment as well as transition to more hydrophilic byproducts.

Removal of perfluoroalkyl acids and dynamic succession of biofilm microbial communities in the decomposition process of emergent macrophytes in wetlands

Perfluoroalkyl acids (PFAAs) are emerging contaminants that pose significant environmental and health concerns. Water–sediment–macrophyte residue systems were established to clarify the removal efficiency of PFAAs, explore possible removal pathways, and profile the dynamic succession of biofilm microbial communities in the decomposition process. These systems were fortified with 12 PFAAs at three concentration levels. Iris pseudacorus and Alisma orientale were selected as the decomposing emergent macrophytes. The removal rates in the treatments with residues of I. pseudacorus (IP) and A. orientale (AO) were 34.4% to 88.9% and 36.5% to 89.9%, respectively, which were higher than those in the control groups (CG) (30.3% to 86.9%), suggesting that decomposition could alter the removal of PFAAs. Sediment made the greatest contributions (preloaded 14.5% to 77.8% of PFAAs in IP, 14.3% to 78.2% in AO, and 27.4% to 71.9% in CG). PFAAs could also be removed by macrophyte residue sorption (0.0190% to 13.0% in IP and 0.016% to 15.6% in AO) and bioaccumulation of residual biofilm (the contributions of biofilm microbes and their extracellular polymeric substances were 0.0110% to 3.93% and 0.918% to 34.4%, respectively, in IP and 0.0141% to 4.65% and 1.49% to 34.1%, respectively, in AO). Significant correlations were observed between sediment/residue adsorption and bioaccumulation of biofilm microbes, and were significantly correlated with perfluoroalkyl chain length (p < 0.05). The dynamic succession of residual biofilm microbial communities was investigated. The largest difference was found at the preliminary stage. The most similar communities were found in AO on day 70 (with specific genera Macellibacteroides and WCHB1-32) and in IP on day 35 (with specific genera Aeromonas and Flavobacterium). This study is useful to understand the removal of PFAAs during the decomposition process, providing further assistance in removing PFAAs during the life cycle of macrophytes in wetlands.

Granular activated carbon adsorption of perfluoroalkyl acids from ground and surface water

AbstractAdsorption of perfluoroalkyl acids (PFAAs) by granular activated carbon (GAC) was evaluated in bench‐, pilot‐, and full‐scale studies to determine effects of PFAA characteristics and background organic matter on carbon use rates. Rapid small‐scale column tests (RSSCTs) were conducted according to the proportional diffusivity (PD) design to assess their suitability to predict full‐ or pilot‐scale GAC performance. PFAA removal from groundwater (GW) and coagulated surface water (SW) was studied with two sub‐bituminous coal‐based GACs. In batch tests conducted with pulverized GAC, the GACs performed similarly in GW, but the GAC with the larger mesopore volume was more effective for PFAA removal from SW. In column tests, carbon use rates decreased with increasing PFAA chain length and were lower for GW (total organic carbon [TOC] = 0.7 mg/L) than for SW (TOC = 2.0–2.7 mg/L). The volume of SW that could be treated to 10% or 50% PFAA breakthrough was about 50–60% of the volume of GW that could be treated when comparing pilot‐scale data for SW with full‐scale data for GW. Consistent differences in PFAA adsorption capacity were not observed for empty bed contact times of 13 and 26 min in full‐scale adsorbers treating GW. The PD‐RSSCT simulating PFAA removal from GW consistently overpredicted full‐scale adsorption capacity, on average by ~70%. Using a carbon use rate of &lt;25 mgGAC/Lwater treated) as a criterion for the feasibility of GAC treatment, full‐ and pilot‐scale GAC adsorber data suggest that GAC is a viable treatment option (carbon use rate &lt; 25 mgGAC/Lwater treated) for perfluoroalkylcarboxylic acids with six or more carbon atoms in SW and five or more carbon atoms in GW. For perfluoroalkyl sulfonic acids, GAC treatment is viable for compounds containing four or more carbons based on results obtained with both SW and GW.

Removal potential of multiple perfluoroalkyl acids (PFAAs) by submerged macrophytes in aquatic environments: Tolerance of Vallisneria natans and PFAA removal in submerged macrophyte-microbiota systems

Perfluoroalkyl acids (PFAAs) have emerged as a global concern in aquatic environment remediation due to their abundance, persistence, bioaccumulation, and toxicity. To comprehensively understand the removal potential of multiple PFAAs by submerged macrophytes in aquatic environments, systematic investigations into the tolerance of the typical submerged macrophyte Vallisneria natans to 12 typical PFAAs and the removal capacity to PFAAs in V. natans-microbiota systems were carried out. Results showed that although PFAAs could induce the accumulation of hydrogen peroxide and malondialdehyde, V. natans was overall resistant to multiple PFAAs with natural concentrations. Catalase is one of the main strategies of V. natans to alleviate PFAA stress. Microbiota can remove 18.10–30.84% of the PFAAs from the water column. 24.35–73.45% of PFAAs were removed from water in V. natans-microbiota systems. The uptake of plant tissues and the bioaccumulation of microbiota were proposed as the main removal processes. The removal rates were significantly correlated with the perfluorinated carbon atoms numbers (p < 0.05). PFAAs and V. natans increased the relative abundance of Betaproteobacteria, Nostocales, Microscillaceae, Sphingobacteriales, SBR1031, Chlamydiales, Phycisphaerae, Caldilineales, Rhodobacterales, and Verrucomicrobiales. The present study suggested that V. natans can be a potential species to remove multiple PFAAs in aquatic environments, and further providing insights into the PFAAs' remediation.

Laboratory and Semi-Pilot Scale Study on the Electrochemical Treatment of Perfluoroalkyl Acids from Ion Exchange Still Bottoms

The ubiquitous presence of perfluoroalkyl acids (PFAAs) in the environment remains a serious environmental concern. In this study, the electrochemical oxidation (EO) of PFAAs from the waste of ion exchange (IX) still bottoms was assessed at the laboratory and semi-pilot scales, using full boron-doped diamond (BDD) electrochemical cells. Multiple current densities were evaluated at the laboratory scale and the optimum current density was used at the semi-pilot scale. The results at the laboratory scale showed &gt;99% removal of total PFAAs with 50 mA/cm2 after 8 h of treatment. PFAAs treatment at the semi-pilot scale showed 0.8-fold slower pseudo-first-order degradation kinetics for total PFAAs removal compared to at the laboratory scale, and allowed for &gt;94% PFAAs removal. Defluorination values, perchlorate (ClO4−) generation, coulombic efficiency (CE), and energy consumption were also assessed for both scales. Overall, the results of this study highlight the benefits of a tandem concentration/destruction (IX/EO) treatment approach and implications for the scalability of EO to treat high concentrations of PFAAs.

Per‐ and polyfluoroalkyl substance removal in carbon‐based advanced treatment for potable reuse

AbstractThe persistence of perfluoroalkyl acids (PFAAs) in wastewater effluent highlights the need for active monitoring and targeted removal of these compounds in potable reuse applications. The City of Altamonte Springs' permanent potable reuse demonstration facility, pureALTA, employs a carbon‐based advanced treatment process using multiple treatment barriers to provide potable water that meets state and federal regulatory requirements and health guidelines for unregulated contaminants. The combination of ozonation, biological activated carbon filtration (BAC), ultrafiltration (UF), granular activated carbon adsorption (GAC), and UV advanced oxidation process (UV AOP) showed complete removal of long‐chain PFAAs (perfluoroalkyl sulfonic acids with ≥6 carbons and perfluoroalkyl carboxylic acids with ≥7 carbons) with federal health guidelines, such as perfluorooctanoic acid and perfluorooctane sulfonate in the advanced treated water while maintaining total organic carbon (TOC) levels below 3 mg/L, the regulatory limit in Florida for indirect potable reuse. Ozone, BAC, and UF showed increases in PFAAs to varying levels based on the transformation of precursors. GAC was the critical process for both TOC and PFAA removal; as anticipated GAC media's age defined the extent of removal of short‐chain PFAAs such as perfluoropentanoic acid and perfluorohexanoic acid. Because of regulatory limits on TOC in Florida potable reuse projects and the absence of regulations on short‐chain PFAAs, TOC continues to dictate GAC media change‐out frequency and operating cost. However, the performance control strategy for GAC at pureALTA may change if stringent limits are set for short‐chain PFAAs in the future. As of May 2021, pureALTA has been in operation for more than 4 years and continues to operate, providing an opportunity for continued research and community engagement.Article Impact StatementThe study represents the first pilot‐scale evaluation of perfluoroalkyl acid removal and correlation to total organic carbon in a carbon‐based advanced treatment process for potable reuse in Florida.

A flow-through cell for the electrochemical oxidation of perfluoroalkyl substances in landfill leachates

A novel boron-doped diamond (BDD) flow-through cell was used to evaluate the electrochemical oxidation of perfluoroalkyl acids (PFAAs) in landfill leachates. Six different leachates with a concentration of individual PFAAs in the range of 102 − 104 ng/L were treated. The performance of the flow-through cell was assessed and compared with synthetic solutions for the oxidation of two representative PFAAs: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Subsequently, the effect of current density and the variability of leachates composition was investigated for the electrochemical oxidation of PFAAs in real landfill leachates. Non-detect levels and >90% degradation was reached for PFOS and PFOA after 2 h of treatment for all leachates tested. Decreasing trends for perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), and perfluorohexanesulphonic acid (PFHxS), and increasing trends for perfluoropentanoic (PFPeA), perfluorobutanoic (PFBA), and perfluorobutanesulphonic acid (PFBS) were observed. The total PFAAs removal ranged from −138.6 to 73.5%. Correlations between the composition of the leachates and PFAAs removal percentages were determined. Overall, the results show the potential of electrochemical oxidation to oxidize PFAAs present in high strength water such as landfill leachates.

Removal of perfluoroalkyl acids (PFAAs) in constructed wetlands: Considerable contributions of submerged macrophytes and the microbial community

The broad application of perfluoroalkyl acids (PFAAs) has attracted global concern regarding their adverse environmental effects. The possible removal processes of PFAAs in constructed wetlands were excavated and quantified using two typical submerged macrophytes (rooted Potamogeton wrightii and rootless Ceratophyllum demersum). Our results showed that 33.59–88.99% of PFAAs could be removed via not only sediment sorption or phytoextraction but also by the bioaccumulation of microbiota. The sediment acts as a vital sink for PFAAs, preloading 23.51–50.09% and 16.65–52.18% of PFAAs in treatments with P. wrightii (Pw1) and C. demersum (Cd1), respectively. C. demersum showed a better capacity to accumulate PFAAs (0.91–32.03%) than P. wrightii (<10%). Considerable PFAAs were observed to be distributed in microbes, underlining the non-negligible role of microbiota in bioaccumulating PFAAs. The contributions of planktonic microbes, biofilm microbes, and extracellular polymeric substances in biofilms were 0.39–20.96%, 0.03–7.95%, and 0.39–14.15% in Pw1 and 0.23–15.68%, 0.01–15.68%, and 0.53–26.77% in Cd1, respectively. The adsorption/uptake was significantly correlated with the perfluoroalkyl chain length (p<0.05), except for the uptake of biofilms in C. demersum. Furthermore, PFAAs and submerged macrophytes could decrease the richness of microbiota but increase the relative abundance of some strains in Betaproteobacteriales, Sphingomonadales, and Cytophagales. Our results were helpful for understanding the removal processes of PFAAs in constructed wetlands and their linkages with PFAA properties, thus further providing insight into the management and removal of emerging organic contaminants.

Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor

A bench-scale plasma reactor was used to degrade poly- and perfluoroalkyl substances (PFAS) in landfill leachate samples obtained from three different locations. In the leachate samples before treatment, five long-chain, six short-chain perfluoroalkyl acids (PFAAs) and eight PFAA precursors were detected in a wide concentration range (~102 to 105 ng/L; total oxidizable precursors (TOP) ~106 ng/L). The concentration of perfluorooctane sulfonate (PFOS) plus perfluorooctanoic acid (PFOA) ranged between 2000 and 3000 ng/L. Plasma-based water treatment of 500 mL samples resulted in faster removal rates for longer-chain than shorter chain length PFAAs. Both PFOS and PFOA were removed to below United States Environmental Protection Agency’s (USEPA’s) health advisory concentration level (HAL) concentrations (<70 ng/L) in 10–75 min; 90% PFOA and PFOS removal was achieved in 10 min. Long-chain and short-chain PFAAs were removed by >99.9% and 10–99.9%, respectively. The removal rate constant (kPFOA+PFOS) for combined PFOA and PFOS ranged between 0.20 and 0.34 min-1. Overall, 60 ± 2% of the TOP concentration and 34 ± 2% of the TOC were removed. No effect of non-PFAS co-contaminants (e.g., total initial organic carbon concentration ~2000 mg/L) on the degradation efficiency was observed. Short-chain PFAA removal efficacy was enhanced by adding a cationic surfactant (cetrimonium bromide). Overall, the results indicate that plasma-based technology may be a viable technology for the treatment of PFAS-contaminated landfill leachates.

Enhanced treatment of perfluoroalkyl acids in groundwater by membrane separation and electrochemical oxidation

This work explores the treatment of poly- and perfluoroalkyl acids (PFAAs) in groundwater by coupling membrane separation and electrochemical oxidation (ELOX). A process system engineering approach based on modelling and empirical data was followed. Two nanofiltration (NF90) and reverse osmosis (BW30) membranes were characterized for treating an electrolyte (NaCl and CaSO4) mixture of perfluorocarboxylic acids (PFCAs) containing PFOA, PFHpA, PFHxA, PFPeA and PFBA with initial concentrations of 10 µg L−1 each. Membrane surface charge shielding and concentration polarization negatively influenced NF90 performance, and the BW30 membrane was selected. Electrochemical oxidation with boron doped diamond anodes treated the PFCAs mixture amended with PFOS and 6:2 FTSA, emulating previously pre-concentrated feed and non-preconcentrated feed conditions. Working at different current densities (J) between 20 and 350 A m−2, the removal of PFOA, PFOS and 6:2 FTSA followed first order apparent kinetics, although shorter chain PFCAs initially showed increasing trends because of their simultaneous electrogeneration and degradation. Overall, ΣPFAA electrolysis followed first order kinetics linearly correlated to J in the full range of testing. Unexpectedly, PFAAs electrolysis was faster for the low conductive non-preconcentrated feed, a result that was ascribed to the enhanced direct electron transfer mechanism resulting from the higher cell voltage. For 99.9% PFAAs removal, the total specific cost of treatment was minimized using a cascade of four RO stages and ELOX treatment of the concentrate, to reach ΣPFAA below the Health Advisory Levels recommended by the USEPA in drinking water (<70 ng L−1 sum of PFOA and PFOS).

Comparative removal of Suwannee River natural organic matter and perfluoroalkyl acids by anion exchange: Impact of polymer composition and mobile counterion

Anion exchange resin (AER) adsorption is an established technology for water treatment and groundwater remediation. Two contaminants amenable to AER treatment are natural organic matter (NOM) and per- and polyfluoroalkyl substances (PFAS), specifically anionic perfluoroalkyl acids (PFAAs) such as perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). NOM is ubiquitous in natural waters and is often targeted for removal. PFAS occurrence in water resources is a human health concern. Accordingly, the goal of this research was to provide new insights on the use of AER for water treatment considering separate and combined removal of NOM and PFAAs. Batch experiments were conducted comparing polystyrene and polyacrylic AER in both chloride- and sulfate-forms using natural groundwater spiked with Suwannee River natural organic matter (SRNOM) and/or six PFAAs. The polymer composition of the AER had a significant impact on contaminant removal with polystyrene resin more effective for PFAA removal and polyacrylic resin more effective for SRNOM removal. Both resins had type I quaternary ammonium functional groups; however, the polyacrylic resin had trimethyl ammonium whereas the polystyrene resin had triethyl ammonium. Therefore, the influence of polymer composition could not be isolated conclusively from functional group chemistry. Polystyrene AER showed greater removal of PFAAs with sulfonate than carboxylate head group and 8-carbon than 4-carbon chain length. Removal of SRNOM and PFAAs by both resin polymer compositions were greater when sulfate was the mobile counterion ion than chloride. The results of this research have important implications for using AER for water treatment and remediation. Foremost, polymer composition and mobile counterion form of the resin can be selected to target specific contaminants and maximize contaminant removal. When contaminants have unique interactions with AER such as SRNOM and polyacrylic resin and PFAAs and polystyrene resin, the presence of one contaminant does not impact removal of the other contaminant.