Conference Agenda

The wide application of per- and polyfluoroalkyl substances (PFAS) has led to their environmental occurrence, resulting in potential uptake and bioaccumulation in plants. For in-situ remediation of PFAS, stabilization that aims to retain pollutants in their original matrix and prevent their movements to surrounding locations is recognized as an effective approach. In the current research, our results showed that carbon-based sorbents such as activated carbon and RemBind products had an outstanding performance in reducing the mobility of perfluoroalkyl acids (PFAAs) in both sewage sludge and soil and lowering the bioavailability of PFAAs to plants in biosolids-amended soil. In this project, we also investigated the effect of activated carbon on the distribution, transformation, and plant uptake of a perfluorooctanesulfonic acid (PFOS) precursor, N-ethyl perfluorooctane sulfonamido acetic acid (N-EtFOSAA), in soil-soybean systems. The results indicated that N-EtFOSAA at 300 µg/kg was taken up by soybean roots and shoots together with its transformation products (i.e., perfluorooctane sulfonamide (PFOSA), PFOS), while decreasing the biomass weight. Powered activated carbon (PAC) amendment significantly reduced the water leachable and methanol extractable N-EtFOSAA and its transformation products in soil. With soybean and after 60 days, 73.5% of the initially spiked N-EtFOSAA became non-extractable bound residues. The PAC addition also decreased the total plant uptake of N-EtFOSAA by 94.96%, indicating that the combination of PAC and soybean was effective in immobilizing N-EtFOSAA in soil. Overall, this study proved the concept that it may be feasible to stabilize PFAS in soil-plant systems when a suitable sorbent is used.

This study, data driven machine learning model was developed to estimate the partitioning of Per- and Poly-fluoroalkyl Substances (PFAS) compounds during aqueous adsorption on various adsorbent materials with a vision to potentially replace the time-consuming and labor-intensive adsorption experiments. Various regression models were trained and tested using previously published data. 290 data points and 170 data points for activated carbon and mineral adsorbents, respectively, were mined for developing the model. 70% of the data points were used for training and 30% was used for testing the models. Statistical parameters, such as Root-Mean-Square Error (RSME), R-Squared, Mean Average Error (MAE), Mean Squared Error (MSE), etc., were used to compare the regression models. It was found that rational quadratic GPR (R-squared = 0.9966) and fine regression tree (R-Squared = 0.9427) models had the highest estimation accuracy for carbon-based and mineral-based adsorbents, respectively. These models were then validated for prediction accuracy using 10 data points from previous studies as an outer test set. Rational quadratic GPR was able to achieve 99% prediction accuracy for carbon-based adsorbent, while fine tree regression model was able to achieve 94% prediction accuracy. Despite such high estimation accuracy, the data mining process revealed the data shortage and the need for more research on PFAS adsorption to present real-world models. This study, as one of the first, shed a light on the determination of key parameters in aquatic chemistry with data mining and machine learning approaches.

Poly- and perfluoroalkyl substances (PFAS) are a broad class of compounds whose chemical stability and amphiphilic properties make them ideal components of aqueous film forming foam (AFFF), used for fire suppression. However, widespread use of these chemicals has led to PFAS concentrations above health advisory limits in environmental media. Many PFAS strongly accumulate at interfaces, which can influence their transport and distribution in multiphase porous media systems. This process is critical in unsaturated soils, where adsorption at the air-water interface can reduce the migration of PFAS through the vadose zone to groundwater. A combined experimental/modeling study was undertaken to investigate the transport of a two-component mixture of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in variably saturated porous media. Modeled processes included: moisture release induced by surface tension changes, non-linear sorption to the solid phase, and competitive adsorption at the air-water interface. The model was validated through comparisons with experimental data for unsaturated transport of individual PFAS and mixtures in columns packed with Ottawa sand (40-270 mesh). Influent concentrations of PFOA and PFOS were 160 and 2.5 mg/L, respectively (levels similar to those in commercial 3% AFFF). A Darcy velocity of 10 cm/d was maintained at a 60% average water saturation. Laboratory observations and model results demonstrate that competitive adsorption at the air-water interface can alter PFAS transport. Consistent with model predictions, PFOA sorbed less in the mixture transport study than was anticipated from its single solute behavior, and its breakthrough curve exhibited concentration overshooting.

Concerns about the presence of PFAS in drinking water have led to a demand for effective treatment methods. IX resins can effectively remove PFAS, including short-chain compounds and poorly understood fluoroethers. However, few studies investigated the kinetics and sorption mechanisms of PFAS uptake by IX resins. In this research, short bed adsorber (SBA) experiments and rapid small-scale column tests (RSSCTs) were conducted with 23 PFAS to (1) determine the rate-limiting mass transfer step, (2) investigate the accuracy of the Gnielinski correlation for predicting film diffusion coefficients, and (3) determine contributions of hydrophobic and electrostatic interactions to PFAS uptake by IX resins by comparing RSSCT results obtained in methanol and groundwater.
We found that PFAS uptake rates were primarily controlled by film diffusion because (1) PFAS breakthrough curves showed almost no discontinuity after flow interruption equivalent to 3 days in RSSCTs and (2) Biot numbers were <5 for all 23 targeted PFAS. Film diffusion coefficients obtained from SBA experiments were within a factor of 1-2.5 of those predicted by the Gnielinski correlation. In methanol RSSCTs, the chain-length dependence of PFAS removal was opposite to that observed in groundwater. Furthermore, PFAS broke through much earlier in methanol RSSCTs than in groundwater RSSCTs, indicating the mechanism of PFAS uptake by IX resins is a combination of electrostatic and hydrophobic interactions, with the relative importance of the latter increasing with increasing PFAS chain length. This research will support the design of IX treatment processes in the context of PFAS remediation and drinking water treatment.

Per- and polyfluoroalkyl substances (PFAS) are increasingly attracting intense attention due to their ubiquity, persistence, bioaccumulative nature, and potential to exert toxicity. There are several sources of errors in PFAS analysis, and adsorption onto containers during sample collection, storage, and experimentation is not negligible. The mass transfer of PFAS from the aqueous phase to container has been rarely studied. Here, we investigated the roles of (1) PFAS (perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid ammonium salt (GenX), perfluorooctanesulfonamide (FOSA), perfluorobutane sulfonic acid (PFBS), and perfluorooctane sulfonic acid (PFOS)), (2) container material (high-density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and glass), (3) temperature (4°C and 20°C), and type of solution (single- or mixed-analyte) on the adsorption of PFAS to containers. In general, PFAS adsorption onto containers was affected by PFAS chain length and functional group, the coexistence of other PFAS, container hydrophobicity and manufacturer, and temperature. PFAS adsorbed to all containers, regardless of materials and temperature. In single-analyte solutions, adsorbed single PFAS ranged from 3.89 ng/cm² to 30.34 ng/cm², with perfluoroalkyl sulfonates adsorbing 2.5 - 6× more onto HDPE and PP containers than their corresponding perfluoroalkyl carboxylates. The PP container, which is widely recommended for studies, adsorbed the highest amount of total PFAS (55.73 ng/cm²) from the mixed-analyte solution. The trend of total PFAS adsorption from the mixture solution was PP > HDPE > PET > glass > PS. The result shows that container characterization for PFAS adsorption is an important step in PFAS studies.