Fuhar Dixit

Evolving global regulations of per- and polyfluoroalkyl substances (PFASs) are driving rapid expansion of sorbent-based treatment in drinking water and industrial effluents. Granular activated carbon and anion-exchange resins remain among the best available technologies, yet the sustainability and cost of full-scale sorbent replacement or regeneration have become critical challenges. Meanwhile, novel adsorbents commonly promise both a higher affinity to remove PFAS and ease of regeneration. Media regeneration can reduce costs and environmental impacts but transfers PFAS into residuals requiring integrated capture, monitoring, and destructive treatment to satisfy compliance expectations. This perspective examines sorbent–regeneration–destruction pathways using implementation-relevant design parameters: residual volume reduction, PFAS mass recovery, and media replacement rate. These design parameters depend on sorption performance, desorption efficiency and kinetics, regenerant demand, solvent recovery, residual composition, and media performance over repeated cycles. We present a systems-level implementation framework linking design parameters and performance metrics with economic and regulatory outcomes and recommend priority data needs for standardized performance reporting to support decision-making.

Perfluoroalkyl sulfonamides (FASAs) have been detected in aqueous film-forming foams (AFFF), municipal wastewater, and consumer products, among others. Although the compounds can be quantified directly by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS–MS), methods that are frequently used to measure poly- and perfluoroalkyl substances (PFASs) for which standards are not available, like the total oxidizable precursor (TOP) assay, 19F-NMR and nontarget analysis often employ solid-phase extraction followed by elution in a polar organic solvent, such as methanol. Volatilization of FASAs during open blowdown of polar organic solvent extracts from soil, sediment, or aqueous samples leads to underestimation of PFAS concentrations. To assess the importance of this loss mechanism, we measured recovery of three FASAs under conditions relevant to environmental analysis. Recoveries of FASAs and other neutral PFAS, including FASAAs and FTCAs, from methanol during the nitrogen blowdown step decreased as analyte concentrations decreased, with recoveries of less than 1% at 2 μg/L (i.e., a concentration corresponding to about 4 ng/L in water samples prior to solid-phase extraction). The addition of 10 mM NaOH prior to the blowdown step improved recoveries to greater than 80% for all FASAs. NaOH addition prior to blowdown also resulted in an approximately 40% increase in the concentrations of precursors detected in diluted AFFF as measured with the total oxidizable precursor (TOP) assay. The increased concentrations could not be explained by analytes for which analytical standards were available. These findings highlight that volatilization during solvent evaporation can be a significant source of analytical bias for a broader class of neutral PFAS, with FASAs serving as an important example.

Aqueous film-forming foams (AFFFs) are a major source of per- and polyfluoroalkyl substances (PFAS) contamination in groundwater and soil. Although PFAS sorption is known to depend on the properties of solid matrices, the roles of organic matter and iron (hydr)oxides remain poorly understood, especially for polyfluorinated compounds. To investigate the interplay between particulate organic matter and iron (hydr)oxides in PFAS-contaminated subsurface environments, we studied the partitioning of neutral, cationic, and anionic PFAS in AFFF to well-characterized solids using the mixed-mode solid-phase extraction (SPE) technique combined with the total oxidizable precursor (TOP) assay. Our results indicated that organic matter consistently enhanced PFAS sorption. In contrast, the effect of goethite, a representative iron-containing mineral, on PFAS sorption varied with PFAS charge. Using three different AFFFs, we found that anionic PFAS exhibited strong sorption regardless of organic matter content, while cationic and zwitterionic PFAS sorbed poorly at circumneutral pH. These trends were more pronounced for iron-coated sand, which showed higher affinity for anionic PFAS. Treatment with ascorbate, a mild reductant, released PFAS associated with iron (hydr)oxides. These findings highlight the importance of iron (hydr)oxides in the retention of anionic PFAS and could be leveraged to manage PFAS mobility through subsurface iron amendments or in situ iron (hydr)oxide formation/dissolution.

Changing climate threatens our water systems: Droughts, fires, and floods disrupt access to safe water and no country is immune. The aging infrastructure crisis offers an opportunity to build resiliency into our future water systems with approaches like (non-)potable reuse. Such strategies require participation by end-users, which we propose can be championed by water utilities through: (1) Raising awareness of water challenges, (2) education about current water realities and opportunities, and (3) providing resources to implement and sustain water solutions.

With growing environmental consciousness, biomaterials (BMs) have garnered attention as sustainable materials for the adsorption of hazardous water contaminants. These BMs are engineered using surface treatments or physical alterations to enhance their adsorptive properties. The lab-scale methods generally employ a One Variable at a Time (OVAT) approach to analyze the impact of biomaterial modifications, their characteristics and other process variables such as pH, temperature, dosage, etc., on the removal of metals via adsorption. Although implementing the adsorption procedure using BMs seems simple, the conjugate effects of adsorbent properties and process attributes implicate complex nonlinear interactions. As a result, artificial neural networks (ANN) have gained traction in the quest to understand the complex metal adsorption processes on biomaterials, with applications in environmental remediation and water reuse. This review discusses recent progress using ANN frameworks for metal adsorption using modified biomaterials. Subsequently, the paper comprehensively evaluates the development of a hybrid-ANN system to estimate isothermal, kinetic and thermodynamic parameters in multicomponent adsorption systems.

Zwitterionic per- and polyfluoroalkyl substances are increasingly detected in aquatic environments. The magnitude of their concentration and increased frequency of detection worldwide raise questions on their presence in drinking water and associated health risk. Scientific knowledge on the identification of treatment technologies to effectively capture such zwitterionic PFAS from contaminated water sources remains largely unknown. In this study, we investigated the application of anionic organic scavenger ion exchange (IX) resins (A860), nonionic IX resins (XAD 4 and XAD 7), PFAS-specific resins (A694 and A592), and Ti₃C₂ MXenes (novel two-dimensional metal carbides) for the removal of select fluorotelomer zwitterionic PFAS from natural waters. The cumulative removal of zwitterionic PFAS at pH ∼ 7 follows the order: Ti₃C₂ MXenes > A694 > A592 > A860 > XAD 4 ∼ XAD 7. Ti₃C₂ MXenes were able to capture >75% of the total influent zwitterionic PFAS and the performance remained consistent in natural and synthetic water. Ti₃C₂ MXenes also exhibited efficient regeneration (>90% recovery) with 0.4 M Na₂SO₃ solution, while the regeneration efficacy of other IX resins generally remained below 20%. Treatment with ∼180 J/cm² UV dosage in the 0.4 M Na₂SO₃ regenerant brine solution yielded >99.9% reduction in the zwitterionic PFAS concentration indicating that UV-sulfite systems exhibit promising potential for the treatment of zwitterionic PFAS concentrates.

Per- and polyfluoroalkyl substances (PFAS) are potential human carcinogens that have been ubiquitously detected in drinking water sources. Ion exchange (IX) resins offer promising potential for the treatment of water sources impacted by high natural organic matter (NOM) and PFAS concentrations. Several kinetic models such as the pseudo-first-order (PFO), pseudo-second-order (PSO) and intraparticle diffusion (ID) have been investigated to examine the PFAS uptake kinetics on IX resins. However, the kinetic parameters are strongly impacted by the sorption test conditions, especially the sorbate-to-sorbent ratio, which were highly variable in past studies, resulting in several discrepancies when comparing published data. This study examined the use of the homogenous surface diffusion model (HSDM) coupled with the equivalent background concentration (EBC) model as an approach to describe competitive uptakes of regulated long- and short-chain PFAS, NOM, and inorganic ions (such as sulphate and nitrate) with IX resins. Kinetic studies confirmed surface diffusion as the rate-limiting step in NOM-rich waters (Biot number >30), while the multicomponent equilibrium model demonstrated that the initial NOM concentration of approximately 0.35–0.95 μmol L⁻¹ (C₀ = 5 mg C per L) competed with PFAS for active exchange sites. More importantly, the HSDM (R² > 0.98)/EBC (R² > 0.95) models provided an adequate fit to describe PFAS removal in a recycled wastewater.