Rapid Small-scale Column Tests Research Articles

Remove legacy perfluoroalkyl acids and emerging per- and polyfluoroalkyl ether acids by single-use and regenerable anion exchange resins: Rapid small-scale column tests and model fits

Rapid small-scale column tests (RSSCT) are used to study the removal of per- and polyfluoroalkyl substances (PFAS) for drinking water treatment by ion exchange. Breakthroughs of 15 emerging per- and perfluoroalkyl ether acids and six legacy perfluoroalkyl acid analogs are studied using a single-use PFAS-selective anion exchange resin (AER1) and a regenerable, generic anion exchange resin (AER2). The Bohart-Adams model was used to describe and predict breakthrough, with the modeled results reasonably aligned with RSSCT results in most cases, enabling shorter RSSCT duration for future applications. AER1 exhibited high uptake capacity with no breakthrough for 11 of the 21 tested PFAS during the 144,175 BV continuous operation, allowing compliance with the new National Primary Drinking Water Regulation in many application scenarios. AER2 exhibited much faster breakthroughs for most PFAS and is not a promising option for drinking water treatment. However, the summed PFAS capacity via model fit and total PFAS adsorbed via measurement were only <0.01 % of both resin capacities at full breakthrough, suggesting PFAS could only occupy a tiny portion of the ion exchange sites even for the PFAS-selective AER1. Ether group insertion in the PFAS group leads to later breakthrough, and linear isomers were better captured by the resins than the branched isomers. Overall, PFAS uptake capacity increases and kinetics decrease when the PFAS molecular volume increases. Regeneration using 10 % NaCl solutions partially released PFAS from AER2 but not from AER1, with more short-chain PFAS released than long-chain ones. Ether group insertion decreased the PFAS recoveries during the regeneration of AER2. The regenerated resins showed much faster breakthroughs than the pristine resins, making them unfavorable for drinking water treatment applications. Adsorption displacement of short-chain PFAS by long-chain PFAS was observed in pristine AER1, and post-regeneration leaching occurred for both resins, both phenomena making the resins a possible PFAS source in long-term use.

Adsorption of the fungicide carbendazim on activated carbon: analysis of isotherms, kinetics, rapid small-scale column tests, and impacts of the presence of organic matter

Abstract The adsorption of the fungicide carbendazim (CBZ) on granular activated carbon (GAC) made from bovine bone was investigated in deionized water (DW) and DW with the addition of natural organic matter (DWNOM). The study included tests of isotherms, kinetics, and rapid small-scale column tests (RSSCT). The Freundlich model represented better the adsorption of the fungicide in both matrices, while the pseudo-second-order model fitted better in DW. The isotherm and kinetic studies showed the interference of NOM in the adsorption of CBZ through changes in the parameters of the applied models. In RSSCT, the breakthrough time was faster in DWNOM than in DW. Nevertheless, the CBZ concentrations of both matrices were considered statistically similar for most contact times in RSSCT. In the fixed-bed experiments, the organic matter did not cause significant changes in the adsorption of CBZ in GAC. The NOM presence may have improved the efficiency of GAC in adsorbing CBZ in kinetic and RSSCT tests. There is no knowledge of a similar approach to studying the adsorption of CBZ on GAC in Brazil, mainly using fixed-bed studies. In this way, the present work contributes to a better understanding of the adsorption of carbendazim through the methods used.

Predicting per‐ and polyfluoroalkyl substances removal in pilot‐scale granular activated carbon adsorbers from rapid small‐scale column tests

AbstractPer‐ and polyfluoroalkyl substances (PFAS) occur widely in drinking water, and consumption of contaminated drinking water is an important human exposure route. Granular activated carbon (GAC) adsorption can effectively remove PFAS from water. To support the design of GAC treatment systems, a rapid bench‐scale testing procedure and scale‐up approach are needed to assess the effects of GAC type, background water matrix, and empty bed contact time (EBCT) on GAC use rates. The overarching goal of this study was to predict PFAS breakthrough curves obtained at the pilot‐scale from rapid small‐scale column test (RSSCT) data. The scale‐up protocol was developed for pilot data obtained with coagulated/settled surface water (TOC = 2.3 mg/L), three GACs, and two EBCTs. Between 7 and 11 PFAS breakthrough curves were available for each pilot column. RSSCT designs were investigated that assumed intraparticle diffusivity is independent of GAC particle size (i.e., constant diffusivity [CD]) or linearly dependent on GAC particle size (i.e., proportional diffusivity [PD]). CD‐RSSCTs effectively predicted the bed volumes of water that could be treated at the pilot‐scale to reach 50% breakthrough (BV50%) of individual PFAS. In contrast, PD‐RSSCTs overpredicted BV50% obtained at the pilot‐scale by a factor of ~2–3. The shape of PFAS breakthrough curves obtained with CD‐RSSCTs deviated from those obtained at the pilot‐scale, indicating that intraparticle diffusivity was dependent on GAC particle diameter (dp). Using the pore surface diffusion model (PSDM), intraparticle diffusivity was found to be proportional to (dp)0.25 when considering data up to about 70% PFAS breakthrough. This proportionality factor can be used to design RSSCTs or scale up existing CD‐RSSCT data using the PSDM. Using pilot‐scale data obtained with groundwater and wastewater‐impacted groundwater as well as with additional GACs, the developed RSSCT scale‐up approach was validated for PFAS breakthrough percentages up to 70%. The presented methodology permits the rapid prediction of GAC use rates for PFAS removal.

Removal of Per- and Polyfluoroalkyl substances by anion exchange resins: Scale-up of rapid small-scale column test data

Anion exchange (IX) is a readily implementable water treatment method that can effectively remove per- and polyfluoroalkyl substances (PFAS). The overarching objective of this research was to predict PFAS removal in full- or pilot-scale packed-bed IX resin contactors from rapid small-scale column test (RSSCT) data. Specific objectives were to (1) assess the effects of IX resin crushing on total anion exchange capacity and packed bed density, (2) determine the effects of initial PFAS concentration on PFAS uptake capacity, (3) determine the rate-limiting step controlling PFAS uptake kinetics, (4) determine the effects of hydraulic loading rate on PFAS uptake capacity, and (5) link constant diffusivity RSSCT data to pilot test data to develop a scale-up protocol. Experiments were conducted with two single-use IX resins and three water matrices, including coagulated surface water and groundwater.Crushing IX resin did not substantially change the bed density and total anion exchange capacity, but the morphology of particles changed from almost perfectly spherical to irregularly shaped. PFAS uptake capacity was independent of influent PFAS concentrations in the 30–300 ng/L range. This finding facilitated the development of an RSSCT scale-up approach because influent PFAS concentrations in RSSCTs and corresponding pilot tests often differ. Biot number values and data from interrupted RSSCTs demonstrated that film diffusion or a combination of film diffusion and intraparticle diffusion controls the rate of PFAS uptake by IX resins. From RSSCTs with identical empty bed contact times but different hydraulic loading rates (vf), PFAS uptake capacity was found to be a function of the square root of the product of Sherwood number and particle shape factor (Sh×ϕ). Using a constant diffusivity RSSCT design with a reduced vf, full- or pilot-scale PFAS breakthrough data can therefore be predicted by multiplying the bed volumes of water treated in the RSSCT by a factor of (Shpilot×ϕpilot)/(ShRSSCT×ϕRSSCT) . This research will support the design of future IX treatment processes in the context of PFAS remediation and drinking water treatment.

Trace Organic Contaminant Removal from Municipal Wastewater by Styrenic β-Cyclodextrin Polymers.

Trace organic contaminants (TrOCs) present major removal challenges for wastewater treatment. TrOCs, such as perfluoroalkyl and polyfluoroalkyl substances (PFAS), are associated with chronic toxicity at ng L-1 exposure levels and should be removed from wastewater to enable safe reuse and release of treated effluents. Established adsorbents, such as granular activated carbon (GAC), exhibit variable TrOC removal and fouling by wastewater constituents. These shortcomings motivate the development of selective novel adsorbents that also maintain robust performance in wastewater. Cross-linked β-cyclodextrin (β-CD) polymers are promising adsorbents with demonstrated TrOC removal efficacy. Here, we report a simplified and potentially scalable synthesis of a porous polymer composed of styrene-linked β-CD and cationic ammonium groups. Batch adsorption experiments demonstrate that the polymer is a selective adsorbent exhibiting complete removal for six out of 13 contaminants with less adsorption inhibition than GAC in wastewater. The polymer also exhibits faster adsorption kinetics than GAC and ion exchange (IX) resin, higher adsorption affinity for PFAS than GAC, and is regenerable by solvent wash. Rapid small-scale column tests show that the polymer exhibits later breakthrough times compared to GAC and IX resin. These results demonstrate the potential for β-CD polymers to remediate TrOCs from complex water matrices.

Enabling in situ electro-regeneration systems for PFOA-laden spent activated carbon adsorbents reuse

Adsorption is the main commercially used water treatment technology to remove per-and polyfluoroalkyl substances (PFAS) from water. Despite the high performance of this physical separation treatment, the endpoint of this technology is the production of PFAS-laden spent activated carbon. So far, several regeneration techniques have been used for spent activated carbon. However, activated carbon regeneration techniques remain challenging due to a limited understanding of cost/benefit analysis. In the present study, we developed the first proof of concept in situ electro-regeneration technique for the regeneration of perfluorooctanoic acid (PFOA, as a model long chain PFAS compound) laden-F400 using electro-assisted up-flow rapid small-scale column test (RSSCT) setup. The laboratory column experiments were conducted exploring sequential adsorption and electro-regeneration cycles. The results showed that the electro-regeneration of saturated F400 reinstated up to ∼60% of initial capacity. After the 1st regeneration cycle, the regeneration efficiency of spent F400 remained similar following 4 consecutive adsorption/regeneration cycles. The calculated operational cost for electro-regeneration was 0.70 kWh/kg, which is more competitive than current regeneration techniques. Overall, this novel proof-of-concept approach can be used as a promising alternative regeneration technique to existing ones to minimize waste PFAS-laden adsorbents in landfills and decrease the amount of CO2 emissions associated with the incineration of these sorbents.

Nitrogen doped residual carbon from gasification slag to enhance trifluoroacetate adsorption in groundwater: Experiments and calculations

In this work, a nitrogen doped residual carbon (RCN) from gasification slag was prepared to adsorb trifluoroacetate (TFA) from groundwater. The physicochemical properties of the residual carbon variants were characterized using BET, SEM, XPS and Boehm titration techniques, which determines the porous structure and basic surface property of RCN. For all residual carbon variants, the TFA adsorption kinetics conform the pseudo-second-order model and isotherm data followed the Langmuir model. The RCN exhibited the highest TFA monolayer adsorption capacity of 24.8 mg/g. Thermodynamics study indicated that TFA adsorption onto these adsorbents was spontaneous and the increasing temperature is not conductive to TFA adsorption. During the rapid small scale column tests, the RCN offered 1390 bed volumes (BV) to 3 μg/L breakthrough which was >4 times higher than did the pristine residual carbon (290 BV). Moreover, the DFT calculations obtained the adsorption strength sequence of sulfate > TFA > nitrate onto nitrogen doped carbon, which manifested most unfavorable effect of sulfate on TFA adsorption. This research offers a theoretical and practice reference for the simultaneous gasification slag utilization and perfluorochemicals purification.

Role of grinding method on granular activated carbon characteristics.

A coconut shell (AC1230CX) and a bituminous coal based (F400) granular activated carbon (GAC) were ground with mortar and pestle (MP), a blender, and a bench-scale ball milling unit (BMU). Blender was the most time-efficient for particle size reduction. Four size fractions ranging from 20 × 40 to 200 × 325 were characterized along with the bulk GACs. Compared to bulk GACs, F400 blender and BMU 20 × 40 fractions decreased in specific surface area (SSA, -23% and -31%, respectively) while smaller variations (-14% to 5%) occurred randomly for AC1230CX ground fractions. For F400, the blender and BMU size fraction dependencies were attributed to the combination of (i) radial trends in the F400 particle properties and (ii) importance of shear (outer layer removal) versus shock (particle fracturing) size reduction mechanisms. Compared to bulk GACs, surface oxygen content (At%-O1s) increased up to 34% for the F400 blender and BMU 20 × 40 fractions, whereas all AC1230CX ground fractions, except for the blender 100 × 200 and BMU 60 × 100 and 100 × 200 fractions, showed 25-29% consistent increases. The At%-O1s gain was attributed to (i) radial trends in F400 properties and (ii) oxidization during grinding, both of which supported the shear mechanism of mechanical grinding. Relatively small to insignificant changes in point of zero charge (pHPZC) and crystalline structure showed similar trends with the changes in SSA and At%-O1s. The study findings provide guidance for informed selection of grinding methods based on GAC type and target particle sizes to improve the representativeness of adsorption studies conducted with ground GAC, such as rapid small-scale column tests. When GACs have radial trends in their properties and when the target size fraction only includes larger particle sizes, manual grinding is recommended.

Comparing PFAS removal across multiple groundwaters for eight GACs and alternative adsorbent

AbstractEight granular activated carbons (GACs) and one alternative adsorbent (AA) were evaluated using rapid small‐scale column tests (RSSCTs) to remove low level per‐ and polyfluoroalkyl substances (PFAS) from several groundwaters. Results suggested variability among waters for adsorbents to reach breakthrough. Time to reach breakthrough appeared to be inversely proportional to the background dissolved organic carbon (DOC). Bituminous GACs (particularly F400 and UC1240LD) were more effective than non‐bituminous. The elution order for PFAS was PFHxA (C6) &gt; PFBS (C4) &gt; PFOA (C8) &gt; PFHxS (C6) &gt; PFOS (C8). Multivariate regression predicted bed volumes at which F400 reached significant exhaustion (defined here as 60%) for PFOA using only two parameters (humic acid, DOC). This merits further study as these parameters could potentially be incorporated into models for predicting PFAS breakthrough. VOCs presence negatively impacted PFAS adsorption on GAC. Relative to GACs, the AA was not nearly as impacted by DOC and showed superior performance.

Pilot-scale removal of persistent and mobile organic substances in granular activated carbon filters and experimental predictability at lab-scale

Present knowledge about the fate of persistent and mobile (PM) substances in drinking water treatment is limited. Hence, this study assesses the potential of fixed-bed granular activated carbon (GAC) filters to fill the treatment gap for PM substances and the elimination predictability from lab-scale experiments. Two parallel pilot filters (GAC bed height 2 m, diameter 15 cm) with different GAC were operated for 1.5 years (ca. 47,000 BV throughput) alongside rapid small-scale column tests (RSSCT) designed based on the proportional diffusivity (PD) and the constant diffusivity (CD) approaches. Background dissolved organic matter (DOM) and a set of 17 target substances were investigated, among them 2-acrylamido-2-methylpropane sulfonate (AAMPS), adamantan-1-amine (ATA), melamine (MEL) and trifluoromethanesulfonic acid (TFMSA). Nine substances were predominantly present in the drinking water used as pilot filter influent (frequencies of detection above 80 %, median concentrations 0.003–1.868 μg/L) and their breakthrough behaviors could be observed: TFMSA was not retained at all, four substances including AAMPS and ATA reached complete breakthrough below 20,000 BV, three compounds were partially retained until the end of operation and oxypurinol was retained completely. The comparable PM candidate and DOM removal performances of both GAC aligns with their very similar surface characteristics and elemental compositions. The agreement of results between RSSCT with the pilot-scale filters were substance specific and no superior RSSCT design could be identified. However, CD-RSSCT provide a conservative removal prediction for most studied compounds. MEL adsorption was significantly underestimated by both RSSCT designs. Using the criterion of a carbon usage rate (with respect to 50 % breakthrough) below 25 mgGAC/Lwater for an economic retention by fixed-bed GAC filters, five (out of nine) substances met the requirement.

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 new method to treat fumigant pesticides-spent granular activated carbon utilizing alkaline hydrolysis

Groundwater treatment of recalcitrant fumigant pesticides (1,2-dibromo-3-chloropropane (DBCP), 1,2-dibromoethane (EDB), 1,2-dichloropropane (DCP), and 1,2,3-trichloropropane (TCP)) often involves a pump and treat system with granular activated carbon (GAC). A novel and promising method of treating the pesticide-spent GAC is based on alkaline hydrolysis, a well-understood abiotic transformation mechanism, that offers a potentially greener approach to conventional thermal regeneration. Here, alkaline hydrolysis of these pesticide chemicals was evaluated under homogeneous (aqueous), and heterogeneous (pesticide spent-GAC) conditions involving bituminous- and coconut-based GAC. Aqueous treatment occurred at elevated pH (pH 12.0–12.4) and the pesticide rate of hydrolysis transformation was first-order (DBCP ≫ TCP ≫ EDB ≫ DCP). Significant pesticide loss (94.95–99.98%) was achieved in both types of GAC (pH 12.0–12.4; 30 d). GAC suspensions held (5 d) at pH 11.0, 12.0, and 12.6, resulted in the DBCP loss of 74%, 89%, and 99%, respectively. The pH dependency of DBCP hydrolysis underscores the correlation between alkaline conditions, aggressive hydrolysis treatment, and reaction time for engineered systems. The estimated time (4–8 min) for full OH- intraparticle diffusion into the GAC from bulk solution was much less than the pesticide hydrolysis half-lives indicating that alkaline hydrolysis treatment of pesticides in GAC was reaction rate limited. Rapid small scale column tests demonstrated that the post-treatment (i.e., base hydrolysis) impact on adsorptive characteristics of the GAC was limited.

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.

Novel protein nanofibril–carbon hybrid adsorbent efficiently removes As(iii), As(v) and other toxic elements from synthetic and natural waters in batch and rapid small-scale column tests

Novel adsorbents produced from β-lactoglobulin, a low-cost milk protein, have shown a high affinity to inorganic As(iii) and As(v).

Investigation of zero-valent iron (ZVI)/H2O continuous processes using multivariate analysis and artificial neural networks

Multivariate statistical techniques and artificial neural networks (ANNs) were used for the analysis, interpretation, and modeling of the results obtained in the study of zero-valent iron (ZVI) reactive beds designed for contaminant removal. A wide range of operating conditions was evaluated through more than 120 rapid small-scale column tests (RSSCT). The production of Fe(II) and Fe(III) species, dissolved oxygen consumption, and pH variation along the reactive bed were used as response variables for evaluating the process performance. Due to the complexity of the system, and the difficulty in defining and fitting kinetic parameters, ANN models were used to simulate the system without the need for kinetic expressions. Therefore the latter were used for assessing the system behavior within the investigated experimental domain and for evaluating the relative importance of the operating factors. In addition, the application of the multivariate techniques cluster analysis (CA) and principal component analysis (PCA) revealed underlying relationships among the response variables. Moreover, although multiple physicochemical processes are involved, the results obtained through PCA indicate that the main trends can be rationalized by considering a few key reactions only. The strategy of analyzing RSSCT results with different numerical techniques provides valuable knowledge for designing real-scale ZVI-based treatments aimed at the efficient elimination of a wide range of contaminants in the aqueous phase.

Interactions between H2O2 and dissolved organic matter during granular activated carbon-based residual H2O2 quenching from the upstream UV/H2O2 process

Granular activated carbon (GAC) filtration can be employed to synchronously quench residual H2O2 from the upstream UV/H2O2 process and further degrade dissolved organic matter (DOM). In this study, rapid small-scale column tests (RSSCTs) were performed to clarify the mechanisms underlying the interactions between H2O2 and DOM during the GAC-based H2O2 quenching process. It was observed that GAC can catalytically decompose H2O2, with a long-lasting high efficiency (>80% for approximately 50,000 empty-bed volumes). DOM inhibited GAC-based H2O2 quenching via a pore-blocking effect, especially at high concentrations (10 mg/L), with the adsorbed DOM molecules being oxidized by the continuously generated ·OH; this further deteriorated the H2O2 quenching efficiency. In batch experiments, H2O2 could enhance DOM adsorption by GAC; however, in RSSCTs, it deteriorated DOM removal. This observation could be attributed to the different ·OH exposure in these two systems. It was also observed that aging with H2O2 and DOM altered the morphology, specific surface area, pore volume, and the surface functional groups of GAC, owing to the oxidation effect of H2O2 and ·OH on the GAC surface as well as the effect of DOM. Additionally, the changes in the content of persistent free radicals in the GAC samples were insignificant following different aging processes. This work contributes to enhancing understanding regarding the UV/H2O2-GAC filtration scheme, and promoting the application in drinking water treatment.

Validating the use of lyophilized natural organic matter as background material in GAC rapid small-scale column tests

Utilities often test the effectiveness of different granular activated carbons (GACs) to determine which is most advantageous for their system. For surface water systems, in particular, the seasonal and annual variability of natural organic matter (NOM) in the source water makes it difficult to benchmark the effectiveness of GACs over multiple contract periods. This study produced stable, lyophilized NOM from the filtered water (FW), i.e., the influent to GAC contactors, which was then reconstituted (Recon) and tested against the FW itself in parallel rapid small-scale column tests (RSSCTs). The results demonstrated nearly identical NOM breakthrough profiles. RSSCTs conducted with both FW and Recon were shown to simulate the full-scale contactor performance well, while similar RSSCTs with regenerated GAC yielded a slightly earlier breakthrough, possibly due to the changes in GAC characteristics during regeneration and grinding. RSSCTs evaluating the removal of microcystin-LR (MC-LR) in the presence of background NOM contained in FW and Recon showed slightly different results, possibly due to the difference in chloride concentrations of these two waters. This work validates that reconstituted lyophilized NOM can be used as a source water surrogate for GAC evaluations when the constituent of interest is NOM, and potentially for other constituents depending upon the influence of additional inorganic constituents that were not evaluated as part of this study.

Assessing explicit models of per- and polyfluoroalkyl substances adsorption on anion exchange resins by rapid small-scale column tests

Managing per- and polyfluoroalkyl substance (PFAS) contamination has gained worldwide attention due to their ubiquitous occurrence in water systems. Anion exchange resins (AERs) have been proven effective in removing both long-chain and short-chain PFASs. In this study, an explicit model was developed to describe the breakthrough behavior of an individual PFAS as a single solute onto anion exchange resin in a column filtration process. The model was further modified to predict the breakthrough curve of co-existing PFASs on AER in multi-solute systems by incorporating a separation factor describing the competitive adsorption and a blockage factor describing the loss of adsorption sites. Rapid small-scale column tests (RSSCTs) were performed with six AERs of various properties and three model PFASs in both single- and multi-solutes systems. The breakthrough behaviors of RSSCTs for both single- and multi-solute systems were found adequately described by the models developed in this study. The experiments and accompanied model simulations reveal some important relationships between the AER performance and the properties of both the AERs and the PFASs.

High Efficiency Regeneration Performance of Exhausted Activated Carbon by Superheated Steam and Comparison with Conventional Chemical Regeneration Method

Spent activated carbon is a common by-product of pollution treatment with granular activated carbon (GAC) adsorption and therefore spent activated carbon treatment for reuse is critical to maximize cost-effectiveness and sustainability. Superheated steam regeneration is a novel treatment technology that uses water vapor and is more energy- and cost-efficient than other thermal regeneration methods. This work has value in that two modes of operation are compared in a small-scale process, whose experiment is well designed to reflect its large-scale process. Our study evaluated the effects of superheated steam regeneration on phenol-saturated activated carbon using a rapid small-scale column test (RSSCT) and evaluated this approach with the conventional chemical regeneration method. Our findings indicated that superheated steam regeneration achieved optimal performance at 500°C for 60 min, whereas chemical regeneration performance was optimal using 4% NaOH coupled with a low flow rate. Based on these observations, cyclic adsorption/regeneration tests were conducted six times. Additionally, differences on the carbon surface after regeneration were explored via scanning electron microscopy (SEM). The results indicated that superheated steam was more efficient and rendered cleaner carbon surfaces.

Leveraging DOM UV absorbance and fluorescence to accurately predict and monitor short-chain PFAS removal by fixed-bed carbon adsorbers

Carbon adsorbent fouling by dissolved organic matter (DOM) inhibits the ability of the widely-used rapid small-scale column test (RSSCT) to accurately predict the removal of organic micropollutants (OMP) from water by full-scale carbon adsorbers. Here, the adsorption of 11 short-chain per-/poly-fluoroalkyl substances (PFAS) from groundwater, surface water, and wastewater was examined in pilot columns as well as RSSCTs using constant diffusivity (CD) and proportional diffusivity (PD) designs. Neither the CD- or PD-RSSCT accurately predicted pilot adsorber breakthrough of PFAS using standard diffusional mass transfer models. However, PFAS breakthrough relative to optical property (e.g., peak C, UV absorbance at 254 nm) breakthrough remained constant between pilot column, CD-RSSCT, and PD-RSSCT designs. This finding permitted accurate breakthrough predictions for the sum of PFAS and for 9 of the 11 PFAS on an individual basis in pilot columns using RSSCTs. Multiple linear regressions incorporating influent and treated water optical parameters enabled the modeling approach to be applied to water sources with heterogeneous DOM characteristics. It is hypothesized that this methodology was successful because (i) optical parameters adequately quantified the competitive nature of DOM and their adsorption behaved similar to OMP and (ii) competitive adsorption by low-molecular weight DOM was the predominant fouling mechanism. An OMP monitoring approach was developed for waters containing DOM with heterogenous characteristics that also relied on raw and treated water optical properties. UVA254 and fluorescence monitoring could therefore enable water treatment to remove PFAS in a variety of scenarios that face inhibitory cost and analytical limitations, such as decentralized and low-resource settings.