Rapid Small-scale Column Tests Research Articles

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 <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 < 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.

Per‐ and polyfluoroalkyl substances removal with granular activated carbon and a specialty adsorbent: A case study

AbstractRemoval of per‐ and polyfluoroalkyl substances (PFAS) from water sources is of significant interest as many states have established limits. Three granular activated carbons (GACs) and a clay‐based adsorbent, Fluoro‐sorb® 200 (FS200), were tested using rapid small scale column tests (RSSCTs) to compare relative performance of the media for PFAS removal. FS200 effluent was below detection for all PFAS except PFHxA at 300,000 bed volumes (BVs). The three GACs performed similarly except for PFBS and PFHxA. FS200 showed higher BVs to breakthrough, required a significantly shorter empty bed contact time, and had higher hydraulic loading rate, translating into a smaller footprint than GAC. This work provides important contributions to the water treatment literature, including RSSCT evaluation of FS200 media and media life comparison of GAC and FS200 in drinking water matrices with low PFAS and organic carbon concentrations.Article Impact StatementUtilities needing PFAS treatment will benefit from the testing methodology and results.

Extending granular activated carbon (GAC) bed life: A column study of in-situ chemical regeneration of pesticide loaded activated carbon for water treatment

In-situ chemical regeneration of granular activated carbon (GAC) may represent an advantageous alternative to conventional off-site thermal regeneration in water treatment applications. The performance of chemical regeneration of carbon exhausted by metaldehyde and isoproturon was investigated using rapid small-scale column tests, performed using a sequence of pesticide adsorption and chemical regeneration cycles with a novel alkaline-organic regenerant solution. A fresh regenerant solution was able to achieve 82% and 45% regeneration of carbon exhausted by metaldehyde and isoproturon, respectively. After the first regeneration, the performance declined slightly to 79%, and to 36% after the fourth regeneration. A comparison using a thermally regenerated (operational) carbon suggested that chemical regeneration was more beneficial for carbon exhausted by metaldehyde. The regenerant solution has a potential to be re-used multiple times, thereby minimizing the amount of waste chemicals generated. A series of carbon characterization tests showed that chemical regeneration did not alter the surface area, pore size distribution and surface chemistry of the carbon. As part of the evaluation, the adsorption thermodynamics of virgin and chemically regenerated carbons were determined using isothermal titration calorimetry to evaluate the adsorption behaviour of the pesticides on the carbon samples. The relatively high regeneration efficiency achieved by chemical regeneration, and minimal deleterious effect to the physico-chemical properties of the carbon, demonstrated the beneficial potential of this process as an alternative to conventional thermal regeneration of GAC.

Perfluoroalkyl substances (PFAS) adsorption in drinking water by granular activated carbon: Influence of activated carbon and PFAS characteristics

Perfluoroalkyl substances (PFAS) persistence in the environment leads to their presence in drinking water, that is of high concern due to their potential human health risk. Adsorption onto activated carbon (AC) has been identified as an effective technique to remove PFAS. Adsorption isotherms and breakthrough curves, determined by rapid small-scale column tests (RSSCTs), were studied for eight PFAS and four granular ACs, characterized by different origins, porosities and numbers of reactivation cycles. Both batch and RSSCT results highlighted the strong interaction of AC and PFAS characteristics in adsorption capacity. The most important factor affecting AC performance is the surface charge: a positively-charged AC showed higher adsorption capacities with greater Freundlich constants (KF) and later 50% breakthroughs compared to the AC with neutral surface. Among the positively-charged ACs, a microporous AC demonstrated higher adsorption capacities for hydrophilic and marginally hydrophobic PFAS, while the mesoporous AC performed better for more hydrophobic PFAS, possibly due to lower pore blockage by organic matter. These results were confirmed at full-scale through a one-year monitoring campaign, in which samples were collected at the inlets and outlets of GAC systems in 17 drinking water treatment plants spread in a wide urban area, where the four analyzed ACs are used.

Modeling and experimental approaches for determining fluoride diffusion kinetics in bone char sorbent and prediction of packed-bed groundwater defluoridator performance

Fluoride (F) in groundwater (GW) in excess of 1.5 mg/L is a globally distributed problem impacting the health of hundreds of millions of people, many of whom cannot access centralized treatment infrastructure. Animal (e.g., cow) bone char has received emerging interest as a low-cost F sorbent for use in decentralized household and community water treatment. Pilot column tests using full-sized granular bone char particles can be used to assess treatment performance of fixed-bed contactors, but are costly, time consuming, and require large amounts of test water. Rapid small-scale column tests (RSSCTs) can be used to simulate F uptake in bone char contactors if the relationship between F intraparticle diffusion kinetics and bone char particle size is known. Two common approaches to the RSSCT assume either constant (CD) or linear proportional (PD) sorbate diffusivity as a function of sorbent particle size. This study used experimentally determined pseudo-equilibrium and kinetic F sorption data in model groundwater as inputs to the homogeneous surface diffusion model (HSDM) to determine F intraparticle diffusion coefficients for different-sized bone char particles, and to fit RSSCT and pilot column breakthrough data to evaluate CD and PD approaches. Results of this study, corroborated by incorporation of additional literature data, indicate approximately linearly proportional diffusivity of F as a function of bone char particle size. Congruently, the PD-RSSCT approach provided a superior simulation of pilot column F breakthrough compared to the CD-RSSCT. PD-RSSCT breakthrough data closely matched pilot breakthrough on a scaled service time basis up to around 500 bed volumes, corresponding to a relative F breakthrough of about 40%, and provided a slightly conservative indicator of F removal thereafter. The PD-RSSCT was compared with a hybrid modeling and empirical workflow using the HSDM with experimentally determined pseudo-equilibrium and kinetic parameter inputs as time-and-cost-saving approaches to evaluating full-sized groundwater treatment system performance. This comparison and a sensitivity analysis of HSDM input parameters used in the hybrid workflow indicated that greater precision can be obtained using the PD-RSSCT.

Asenic removal from groundwater using granular chitosan-titanium adsorbent

Arsenic (As) contamination poses an urgent environmental risk, and its removal from groundwater remains a challenge due to the lack of efficient adsorbents. Herein, a novel granular chitosan-titanium (CS-Ti) adsorbent was fabricated by the sol-gel method. Batch experiments show that As(V) adsorption on CS-Ti followed the pseudo-second-order kinetic model, and the adsorption isotherm conformed to the Freundlich model with the correlation coefficient of 0.99. In situ FTIR spectra revealed that the CS-Ti adsorbent was composed of amorphous TiOx and chitosan by forming C-O-Ti and N-Ti bonds, and the amorphous TiOx was responsible for As(V) adsorption. Rapid small-scale column tests show that 165.6 μg/L of As in groundwater were effectively removed in approximately 126-bed volumes, and the spent adsorbents were regenerated with 0.01 mol/L NaOH and maintained the adsorption efficiency after four cycles. This study provides a simple and practical route to fabricate adsorbents for water treatment.

Removing co-occurring contaminants of arsenic and vanadium with full-scale arsenic adsorptive media systems.

The U.S. Environmental Protection Agency conducted an Arsenic Demonstration Program (ADP) whereby 50 full, small-scale arsenic removal treatment systems were evaluated for removing arsenic to below the maximum contaminant level of 10 μg/L and their operating cost for a minimum of 1 year. The majority (28) of the systems installed were adsorptive media (AM) technology with the media replaced when exhausted. This paper reports on the results of two ADP projects and two laboratory rapid small-scale column tests (RSSCTs) using the iron-based media, Bayoxide E33 (E33) AM for the removal of arsenic (As) and the co-occurring contaminants (COCs) of vanadium and to a lesser degree fluoride (F) and nitrate (NO3). The ADP studies found that the AM effectively removed the COC of V, but with a lower removal capacity than of As. One ADP study found the AM to be ineffective for the removal of F and NO3. The RSSCT conducted on two other source waters also found vanadium to be removed by the same AM. The study results suggested the AM selectively sequence of As > V > F = N. The study also investigated the AM to achieve an As limit of 5 μg/L. The AM was found to reduce As to below 5 μg/L with around 30% shorter treatment run lengths.

Batch and Continuous Design of a Full‐Scale Treatment Facility for Removing Dissolved Natural Organic Matter

AbstractBatch and continuous flow adsorption experiments are carried out and the design of a full‐scale facility for removing dissolved natural organic matter (DNOM) from Catalan Lakewater is demonstrated. The adsorption efficiency is proportional to the temperature and the amount of adsorbent unlike pH increase. The highest DNOM removal rate is obtained at 35 °C, pH 4, and an adsorbent amount of 0.8 g L−1. Optimum contact time for batch studies is 60 min at equilibrium. Correlation constants (r) of Langmuir and Freundlich isotherms are 0.8905 and 0.9739, respectively. Based on the Freundlich isotherm, the highest adsorption capacity (qmax) obtained is 2.44 and 6.01 mg DNOM/g granulated activated carbon (GAC) for raw and enriched water, respectively. Consequently, the effects of adsorbent amount, bed depth, empty bed contact time, and organic loading on removal performance are investigated in the rapid small‐scale column test (RSSCT) columns. The targeted effluent concentration of 1 mg DNOM/L can easily be achieved in the columns. At the design capacity of the facility, 15 adsorption columns with dimensions of 7 m height, 4.33 m diameter, and 22 days of operation cycle are required to remove DNOM from raw water.

Mesoporous structure regulation of activated carbons and effects on the synergistic efficacy of synchronous adsorption and bio-degradation in biological activated carbon process

Abstract Mesoporous activated carbon MCGL-4 was tailored for simultaneous enhancement of adsorption and bio-degradation by multistage depth-activation (MDA). Synergistic efficacy of synchronous adsorption and bio-degradation was evaluated in pilot-scale bio-enhanced activated carbon (BEAC) system. Results identified that MCGL-4 obtains synchronously well-developed meso- (0.7605 cm3/g), micro- (0.2655 cm3/g) and macro-porous (0.143 cm3/g) structures. Higher volume during 20.4–208.2 Å (0.6848 cm3/g) ensured higher adsorption capacities for natural organic matters (NOM). The initial immobilized biomass and stabilities on MCGL-4 were also significantly promoted. Rapid small-scale column tests system (RSSCTs) tests showed that adsorption capacities for humic-like organics were 67,725.32 mg·DOC/(kg·carbon) at 39.50 m3·H2O/(kg·carbon). In BEAC system, MCGL-4 achieved higher removal efficiency for fulvic acid, humic acid and aromatic organic matters than commercial carbons. At 39.50 m3·H2O/(kg·carbon), cumulative uptake of organic-pollutants achieved by MCGL-4 was 94,850.51 mg·DOC/(kg·carbon). The proportion occupied by bio-degradation were 31,674.70 mg·DOC/(kg·carbon). It also confirmed that bio-degradation ability was much higher than commercial carbons after mesoporous structures regulation by MDA process.

Application of Rapid Small-Scale Column Tests for Treatment of Perfluoroalkyl Acids Using Anion-Exchange Resins and Granular Activated Carbon in Groundwater with Elevated Organic Carbon

Rapid small-scale column tests (RSSCTs) are often employed in laboratory testing to determine contaminant treatment effectiveness by anion-exchange resins (AERs) or granular activated carbons (GACs...

Predicting breakthrough of vanadium in fixed-bed absorbent columns with complex groundwater chemistries: A multi-component granular ferric hydroxide−vanadate−arsenate−phosphate−silicic acid system

Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater chemistries. The BTCs were simulated successfully using a homogeneous surface diffusion model (HSDM) combining equilibrium chemical adsorption and kinetic mass transfer. Adsorption parameters for various groundwater compositions were predicted using the CD-MUSIC surface complexation model, which was set up for the first time for akaganéite-based granular ferric hydroxide with a competitive multi-solute system. The results indicated that V(V) is less prone to competitive adsorption effects, and use of the homogeneous surface diffusion model to predict the BTCs requires then the kinetic mass transfer Biot number to be used as the only fitting parameter. On the other hand, a concentration overshoot could be observed for the two weaker absorbed oxo-anions arsenate and phosphate because of displacement by the vanadate. Results of pilot scale test column BTCs of vanadate for three waterworks with different groundwater compositions could be favorably extrapolated with a unique Freundlich constant kF of 3.2 derived on basis of the multi-solute CD-MUSIC model, and a unique Biot number of 37 fixed for all three different test sites.

Use of rapid small-scale column tests for simultaneous prediction of phosphorus and nitrogen retention in large-scale filters

Rapid small-scale column tests (RSSCTs) have been previously used to predict the effluent concentration of a single nutrient in large filters with good accuracy. However, in drainage waters originating from heavy textured soils, where there is a need for in-ditch filters to retain both dissolved reactive phosphorus (DRP) and ammonium (NH4) simultaneously, the suitability of a RSSCT approach to model both parameters must be proved. In this study, a decision support tool was used to identify appropriate media that may be placed in filters for the removal of DRP and NH4. The selected media for this study were sand and zeolite. Both media were placed in acrylic tubes each with an internal diameter of 0.01 m and with lengths ranging from 0.1 to 0.4 m, and their performance for simultaneous removal of DRP and NH4 (1 mg DRP and NH4-N L−1) from water was evaluated. The data generated from the RSSCTs were used to model DRP and NH4 removals in 0.4 m-long laboratory columns of internal diameter 0.1 m, which had the same media configuration as the small columns and were operated using the same influent concentrations. The developed model successfully predicted the effluent concentration of both the DRP and NH4-N from the large columns. This indicates using RSSCTs to model the performance of filters will produce substantial savings in operational, financial and labour costs, without affecting the accuracy of model predictions.

Differentiating between adsorption and biodegradation mechanisms while removing trace organic chemicals (TOrCs) in biological activated carbon (BAC) filters

Efficient adsorption of certain trace organic chemicals (TOrCs) present in secondary treated municipal wastewater treatment plant (WWTP) effluents onto granular activated carbon (GAC) has already been demonstrated at lab- and full-scale. Due to high organic matter concentrations in WWTP effluents, GAC filters eventually develop a biofilm and turn into biological activated carbon filters (BAC), where removal of organic compounds is governed by biodegradation as well as by adsorption. However, determining TOrC breakthrough by conducting a long-term BAC column experiment to discern between the removal mechanisms is not possible due to competition for adsorption sites, fluctuating water quality, and other variables. Therefore, a rapid small scale column test (RSSCT) was conducted to determine the contribution of adsorption for select chemicals at 10,000 bed volumes treated (BVT). These results were then used in the pore surface diffusion model (PSDM) to model adsorption behavior at 40,000 BVTs. Pseudo-Freundlich K values obtained from the PSDM model were compared with K values obtained from an integral mass balance calculation. This comparison revealed that the modeling was most accurate for moderately to poorly adsorptive compounds. In comparing RSSCT results to long-term BAC columns, the modeling approach best predicted BAC removal of well adsorbing compounds, such as atenolol, trimethoprim, metoprolol, citalopram, and benzotriazole. However, differences in predicted vs observed BAC removal for the removals of venlafaxine, tramadol and carbamazepine revealed that BAC adsorption capacity was not yet exhausted for these compounds. Therefore, a comparison was not possible. The approach would be improved by operation at longer EBCT and improved calculation of compound fouling indices.

Adsorption mechanisms of PFOA onto activated carbon anchored with quaternary ammonium/epoxide-forming compounds: A combination of experiment and model studies

When wood-based activated carbon was tailored with quaternary ammonium/epoxide (QAE) forming compounds (QAE-AC), this tailoring dramatically improved the carbon's effectiveness for removing perfluorooctanoic acid (PFOA) from groundwater. With favorable tailoring, QAE-AC removed PFOA from groundwater for 118,000 bed volumes before half-breakthrough in rapid small scale column tests, while the influent PFOA concentration was 200 ng/L. The tailoring involved pre-dosing QAE at an array of proportions onto this carbon, and then monitoring bed life for PFOA removal. When pre-dosing with 1 mL QAE, this PFOA bed life reached an interim peak, whereas bed life was less following 3 mL QAE pre-dosing, then PFOA bed life exhibited a steady rise for yet subsequently higher QAE pre-dosing levels. Large-scale atomistic modelling was used herein to provide new insight into the mechanism of PFOA removal by QAE-AC. Based on experimental results and modelling, the authors perceived that the QAE's epoxide functionalities cross-linked with phenolics that were present along the activated carbon's graphene edge sites, in a manner that created mesopores within macroporous regions or created micropores within mesopores regions. Also, the QAE could react with hydroxyls outside of these pore, including the hydroxyls of both graphene edge sites and other QAE molecules. This latter reaction formed new pore-like structures that were external to the activated carbon grains. Adsorption of PFOA could occur via either charge balance between negatively charged PFOA with positively charged QAE, or by van der Waals forces between PFOA's fluoro-carbon tail and the graphene or QAE carbon surfaces.

Effective removal of perfluorooctanoate from groundwater using quaternary nitrogen-grafted granular activated carbon

In this study, a quaternary nitrogen-grafted activated carbon (SNQ) was synthesized to remove perfluorooctanoate (PFOA) from a groundwater source. Batch isotherm tests and rapid small scale column tests (RSSCTs) were used to evaluated the performance of these variants in removing PFOA from groundwater. When processing groundwater that had been spiked with 200 ng/L PFOA, the SNQ exhibited 201,000 BV to 60 % breakthrough. This was 1.6 times higher than for the pristine SAC (128,000 BV). The longer bed life was attributed to the tailored carbon’s enhanced positively charged surface properties, which were monitored for this SNQ adsorbent by means of X-Ray Photoelectron Spectrometer, Scanning Electron Microscopy and Incremental surface charge titration analysis. Kinetics and isotherm tests show that the SNQ exhibited higher adsorption rate and adsorption capacity than the pristine subbituminous coal based activated carbon (SAC); and this was attributed to SNQ’s retained pore structure, high quaternary nitrogen ratio (0.89 %) and positive charge (0.47 meq/g). Moreover, the positively charged quaternary nitrogen groups onto the SNQ strongly attracted PFOA and lead to higher effective diffusion rates (12.6×10−10 m2/s). In order to test the nature of PFOA sorption, the authors employed a dynamic regeneration protocol using ethanol as an organic solvent; and this protocol restored 73 % PFOA adsorption capacity of the SNQ. In light of this tailored SNQ carbon’s high PFOA adsorption capacity and regenerability, we anticipated this quaternary nitrogen-grafted activated carbon could serve as an excellent adsorbent for PFOA removal from groundwater.

Improvement of Manganese Feroxyhyte's Surface Charge with Exchangeable Ca Ions to Maximize Cd and Pb Uptake from Water.

The surface configuration of tetravalent manganese feroxyhyte (TMFx) was appropriately modified to achieve higher negative surface charge density and, hence, to improve its efficiency for the removal of dissolved Cd and Pb mostly cationic species from water at pH values commonly found in surface or ground waters. This was succeeded by the favorable engagement of Ca2+ cations onto the surface of a mixed Mn-Fe oxy-hydroxide adsorbent during the preparation step, imitating an ion-exchange mechanism between H+ and Ca2+; therefore, the number of available negatively-charged adsorption sites was increased. Particularly, the calcium coverage can increase the deprotonated surface oxygen atoms, which can act as adsorption centers, as well as maintain them during the subsequent drying procedure. The developed Ca-modified adsorbent (denoted as TMFx-Ca) showed around 10% increase of negative surface charge density, reaching 2.0 mmol [H+]/g and enabling higher adsorption capacities for both Cd and Pb aquatic species, as was proved also by carrying out specific rapid small-scale column tests, and it complied with the corresponding strict drinking water regulation limits. The adsorption capacity values were found 6.8 μg·Cd/mg and 35.0 μg·Pb/mg, when the restructured TMFx-Ca adsorbent was used, i.e., higher than those recorded for the unmodified material.

Influence of granular activated carbon media properties on natural organic matter and disinfection by-product precursor removal from drinking water

Operational and financial constraints challenge effective removal of natural organic matter (NOM), and specifically disinfection by-product (DBP) precursors, at remote and/or small sites. Granular activated carbon (GAC) is a widely used treatment option for such locations, due to its relatively low maintenance and process operational simplicity. However, its efficacy is highly dependent on the media capacity for the organic matter, which in turn depends on the media characteristics.The influence of GAC media properties on NOM/DBP precursor removal has been studied using a range of established and emerging media using both batch adsorption tests and rapid small-scale column tests. DBP formation propensity (DBPFP) was measured with reference to trihalomethanes (THMs) and haloacetic acids (HAAs). All GAC media showed no selectivity for specific removal of precursors of regulated DBPs; DBP formation was a simple function of residual dissolved organic carbon (DOC) levels.UV254 was found to be a good surrogate measurement of DBPFP for an untreated water source having a high DOC. Due to the much-reduced concentration of DBP precursors, the correlation was significantly poorer for the coagulation/flocculation-pretreateed water source.Breakthrough curves generated from the microcolumn trials revealed DOC removal and consequent DBP reduction to correlate reasonably well with the prevalence pores in the 5–10 nm range. A 3–6 fold increase in capacity was recorded for a 0.005–0.045 cm3/g change in 5–10 nm-sized pore volume density. No corresponding correlation was evident with other media pore size ranges.

Evaluating the effects of water matrix constituents on micropollutant removal by activated carbon and β-cyclodextrin polymer adsorbents

The performance of adsorbents for the removal of organic micropollutants (MPs) from water can be influenced by the presence of water matrix constituents. The objective of this research was to evaluate the influence of water matrix constituents on the performance of coconut-shell activated carbon (CCAC), porous β-cyclodextrin polymer (CDP), and CDP coated on cellulose microcrystal (CDP@CMC) adsorbents. MP removals were measured in batch experiments for a mixture of 90 MP at 1 μg L−1 and MP breakthrough was measured in rapid small-scale column test (RSSCT) experiments for a mixture of 15 MP at 500 ng L−1. All experiments were performed first with nanopure water, and subsequently with six different water samples collected from two separate groundwater, surface water, and wastewater effluent sources. The results of batch and RSSCT experiments demonstrate more rapid adsorption kinetics and less adsorption inhibition in the presence of matrix constituents for CDP adsorbents relative to CCAC. Further, the treatment capacity of CDP@CMC in the RSSCT experiments was higher than that of CCAC, particularly in more complex water matrices. Statistical analyses were performed to investigate associations between adsorption inhibition among groups of MPs and the concentrations of specific water matrix constituents. For CCAC, adsorption inhibition was observed for all MPs and was primarily attributed to the presence of dissolved organic matter with molar weight less than 1000 Da. For CDP adsorbents, adsorption inhibition was primarily observed for cationic MPs and was attributed to the screening of the negative surface charge of CDP by inorganic ions in water samples with high ionic strength. These data further demonstrate the value of CDP as an alternative adsorbent to CCAC for the removal of MPs during water and wastewater treatment.

Assessment of the breakthrough of micropollutants in full-scale granular activated carbon adsorbers by rapid small-scale column tests and a novel pilot-scale sampling approach

This study aimed to compare three approaches for predicting the service life of full-scale GAC adsorbers for the removal of micropollutants.

Removing per‐ and polyfluoroalkyl substances from groundwaters using activated carbon and ion exchange resin packed columns

AbstractHuman exposure to per‐ and polyfluoroalkyl substances (PFAS) in drinking water is of growing concern as a result of increasing reports of occurrence and potential regulation. Adsorption of PFAS by granular activated carbon (GAC) or ion exchange (IX) resin is a suitable treatment technique. However, few studies compare PFAS removal in continuous flow GAC or IX adsorption systems using real drinking water sources. In this study, rapid small‐scale column tests (RSSCTs) were used to investigate the effects of PFAS type and chain length on adsorption by GAC and IX resin for six groundwaters used as drinking water supplies. Seven PFAS substances with chain lengths of C4–C9 were detected in the groundwaters with the sum of their concentrations (ΣPFAS) ranging from 156 to 7,044 ng/L. Adsorption capacities (qΣPFAS) were calculated to compare the removal capacity among different sorbents and qΣPFAS values ranged from 10.3 to 228 ng PFAS/mg sorbent after about 100,000 bed volumes treated. Coal‐based GACs had higher adsorption capacity compared with coconutshell‐based GAC, which was likely due to higher mesopore and macropore volumes. IX resins performed better than GAC in removing PFAS, but they were not effective in treating short‐chain perfluorocarboxylic acids (PFCAs). Perfluorosulfonic acids (PFSAs) broke through later than PFCAs with the same chain length. Within PFSA or PFCA classes, shorter‐chain PFAS species always broke through before longer‐chain PFAS. Statistical analysis demonstrated that PFAS with higher hydrophobicity and molecular weight are more amenable to GAC adsorption. Empirical models were developed and predicted PFAS breakthrough. By quantifying PFAS selectivity and removal efficiency, this work provides benchmark data for commercially available treatment technologies and guidance toward specific PFAS classes for which new treatment technologies may be most beneficial.