Modeling PFAS Removal Using Granular Activated Carbon for Full-Scale System Design.

Per- and polyfluoroalkyl substances (PFAS) are increasingly of interest to drinking water utilities due to state regulations, the release of federal and state health advisories, and public concern. Pilot-scale data were fitted for 16 PFAS species and five commercial-activated carbons using an open-source pore and surface diffusion model that includes an automated parameter-fitting tool. The estimated model parameters are presented, and an uncertainty analysis was evaluated considering the expected temporal variability of influent concentrations. Expected treatment performance differed between two seasons in the pilot phase for the same carbon, which was not captured by modeled uncertainty. However, modeling results can support a utility's decision to choose activated carbon, and make design and operational decisions that can address changing water production rates and treatment goals. For the utility that undertook this pilot study and their desired treatment goals, granular activated carbon (GAC) was found to be an effective treatment technology for PFAS removal.

Modeled Impacts of Drinking Water Pb Reduction Scenarios on Children's Exposures and Blood Lead Levels.

In recent years, environmental lead (Pb) exposure through drinking water has resulted in community public health concerns. To understand potential impacts on blood Pb levels (BLLs) from drinking water Pb reduction actions (i.e., combinations of lead service lines [LSL] and corrosion control treatment [CCT] scenarios), EPA's Stochastic Human Exposure and Dose Simulation (SHEDS)-Multimedia/Integrated Exposure Uptake and Biokinetic (IEUBK) model was applied for U.S. children aged 0 to <6 years. The results utilizing a large drinking water sequential sampling data set from 15 cities to estimate model input concentration distributions demonstrated lowest predicted BLLs for the "no LSLs" with "combined CCT" scenario and highest predicted BLLs for the "yes LSLs" and "no CCT" scenario. Modeled contribution to BLLs from ingestion of residential drinking water ranged from ∼10 to 80%, with the highest estimated for formula-fed infants (age 0 to <1 year). Further analysis using a "bounding" data set spanning a range of realistic water Pb concentrations and variabilities showed BLL predictions consistent with the sequential sampling-derived inputs. Our study illustrates (1) effectiveness of LSL replacement coupled with CCT for reducing Pb in drinking water and children's BLLs, and (2) in some age groups, under realistic local and residential water use conditions, drinking water can be the dominant exposure pathway.

Occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in Source Water and Their Treatment in Drinking Water.

Per-and polyfluoroalkyl substances (PFAS) occurrence in drinking water and treatment methods for their removal are reviewed. PFAS are fluorinated substances whose unique properties make them effective surface-active agents with uses ranging from stain repellants to fire-fighting foams. In response to concerns about drinking water contamination and health risks from PFAS exposure, the United States Environmental Protection Agency published Health Advisories (HAs) for perfluorooctanoic acid and perfluorooctane sulfonic acid. The occurrence of six PFAS in drinking water has been reported in the Third Unregulated Contaminant Monitoring Rule (UCMR3), and subsequent analysis of the dataset suggested that four percent of water systems reported at least one detectable PFAS compound and 1.3 percent of water systems reported results above the HAs. Many treatment technologies have been evaluated in the literature, with the most promising and readily applied treatment technologies being activated carbon, anion exchange resins, and high-pressure membrane systems. From these data and literature reports, research and data gaps were identified and suggestions for future research are provided.

Method to assess component contribution to toxicity of complex mixtures: Assessment of puberty acquisition in rats exposed to disinfection byproducts.

A method based on regression modeling was developed to discern the contribution of component chemicals to the toxicity of highly complex, environmentally realistic mixtures of disinfection byproducts (DBPs). Chemical disinfection of drinking water forms DBP mixtures. Because of concerns about possible reproductive and developmental toxicity, a whole mixture (WM) of DBPs produced by chlorination of a water concentrate was administered as drinking water to Sprague-Dawley (S-D) rats in a multigenerational study. Age of puberty acquisition, i.e., preputial separation (PPS) and vaginal opening (VO), was examined in male and female offspring, respectively. When compared to controls, a slight, but statistically significant delay in puberty acquisition was observed in females but not in males. WM-induced differences in the age at puberty acquisition were compared to those reported in S-D rats administered either a defined mixture (DM) of nine regulated DBPs or individual DBPs. Regression models were developed using individual animal data on age at PPS or VO from the DM study. Puberty acquisition data reported in the WM and individual DBP studies were then compared with the DM models. The delay in puberty acquisition observed in the WM-treated female rats could not be distinguished from delays predicted by the DM regression model, suggesting that the nine regulated DBPs in the DM might account for much of the delay observed in the WM. This method is applicable to mixtures of other types of chemicals and other endpoints.

Comprehensive assessment of a chlorinated drinking water concentrate in a rat multigenerational reproductive toxicity study.

Some epidemiological studies report associations between drinking water disinfection byproducts (DBPs) and adverse reproductive/developmental effects, e.g., low birth weight, spontaneous abortion, stillbirth, and birth defects. Using a multigenerational rat bioassay, we evaluated an environmentally relevant "whole" mixture of DBPs representative of chlorinated drinking water, including unidentified DBPs as well as realistic proportions of known DBPs at low-toxicity concentrations. Source water from a water utility was concentrated 136-fold, chlorinated, and provided as drinking water to Sprague-Dawley rats. Timed-pregnant females (P0 generation) were exposed during gestation and lactation. Weanlings (F1 generation) continued exposures and were bred to produce an F2 generation. Large sample sizes enhanced statistical power, particularly for pup weight and prenatal loss. No adverse effects were observed for pup weight, prenatal loss, pregnancy rate, gestation length, puberty onset in males, growth, estrous cycles, hormone levels, immunological end points, and most neurobehavioral end points. Significant, albeit slight, effects included delayed puberty for F1 females, reduced caput epidydimal sperm counts in F1 adult males, and increased incidences of thyroid follicular cell hypertrophy in adult females. These results highlight areas for future research, while the largely negative findings, particularly for pup weight and prenatal loss, are notable.

Polanyi adsorption potential theory for estimating PFAS treatment with granular activated carbon.

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that have gained interest because some PFAS have been shown to have negative health effects and prolonged environmental and biological persistence. Chemicals classified as PFAS have a wide range of chemical moieties that impart widely variable properties, leading to a range of water treatment process efficacies. The Polanyi Potential Adsorption Theory was used to estimate Freundlich isotherm parameters to predict the efficacy of granular activated carbon (GAC) treatment for 428 PFAS chemicals for which the vast majority had no previously published treatment data. This method accounts for the physical/chemical characteristics of the individual PFAS beyond molecular weight or chain length that have previously been employed. From a statistical analysis of available data and model results, many of the 428 PFAS were predicted to be effectively treatable by GAC. Although not directly applicable to full-scale design, the approach demonstrates a systematic method for predicting the effectiveness of GAC where isotherm or column data are not available. This then can be used to prioritize future research.

Impact of phosphate addition on PFAS treatment performance for drinking water.

Adding new unit operations to drinking water treatment systems requires consideration of not only efficacy for its design purpose but also costs, water quality characteristics, impact on overall regulatory compliance, and impact of other treatment unit operations. Here, pilot study results for ion exchange (IX) and granular activated carbon (GAC) are presented for a utility with both per- and polyfluoroalkyl substances (PFAS) and volatile organic contaminant removal needs. Specifically, the impact of upstream air stripping and phosphate addition on PFAS treatment performance was evaluated. Modeling was used to fit the IX and GAC pilot data and predict performance under different scenarios. GAC performance was generally consistent for treating water before or after the air stripper, but the addition of phosphate prior to air-stripping resulted in a loss of 15%-25% capacity for some PFAS on IX media, demonstrating the need to consider the entire treatment train before implementing PFAS removal unit operations.

Microwave-assisted green synthesis of silver nanostructures.

Over the past 25 years, microwave (MW) chemistry has moved from a laboratory curiosity to a well-established synthetic technique used in many academic and industrial laboratories around the world. Although the overwhelming number of MW-assisted applications today are still performed on a laboratory (mL) scale, we expect that this enabling technology may be used on a larger, perhaps even production, scale in conjunction with radio frequency or conventional heating. Microwave chemistry is based on two main principles, the dipolar mechanism and the electrical conductor mechanism. The dipolar mechanism occurs when, under a very high frequency electric field, a polar molecule attempts to follow the field in the same alignment. When this happens, the molecules release enough heat to drive the reaction forward. In the second mechanism, the irradiated sample is an electrical conductor and the charge carriers, ions and electrons, move through the material under the influence of the electric field and lead to polarization within the sample. These induced currents and any electrical resistance will heat the sample. This Account summarizes a microwave (MW)-assisted synthetic approach for producing silver nanostructures. MW heating has received considerable attention as a promising new method for the one-pot synthesis of metallic nanostructures in solutions. Researchers have successfully demonstrated the application of this method in the preparation of silver (Ag), gold (Au), platinum (Pt), and gold-palladium (Au-Pd) nanostructures. MW heating conditions allow not only for the preparation of spherical nanoparticles within a few minutes but also for the formation of single crystalline polygonal plates, sheets, rods, wires, tubes, and dendrites. The morphologies and sizes of the nanostructures can be controlled by changing various experimental parameters, such as the concentration of metallic salt precursors, the surfactant polymers, the chain length of the surfactant polymers, the solvents, and the operation reaction temperature. In general, nanostructures with smaller sizes, narrower size distributions, and a higher degree of crystallization have been obtained more consistently via MW heating than by heating with a conventional oil-bath. The use of microwaves to heat samples is a viable avenue for the greener synthesis of nanomaterials and provides several desirable features such as shorter reaction times, reduced energy consumption, and better product yields.

Developmental toxicity evaluations of whole mixtures of disinfection by-products using concentrated drinking water in rats: gestational and lactational effects of sulfate and sodium.

A developmental toxicity bioassay was used in three experiments to evaluate water concentrates for suitability in multigenerational studies. First, chlorinated water was concentrated 135-fold by reverse osmosis; select lost disinfection by-products were spiked back. Concentrate was provided as drinking water to Sprague-Dawley and F344 rats from gestation day 6 to postnatal day 6. Maternal serum levels of luteinizing hormone on gestation day 10 were unaffected by treatment for both strains. Treated dams had increased water consumption, and increased incidences of polyuria, diarrhea, and (in Sprague-Dawley rats) red perinasal staining. Pup weights were reduced. An increased incidence of eye defects was seen in F344 litters. Chemical analysis of the concentrate revealed high sodium (6.6 g/l) and sulfate (10.4 g/l) levels. To confirm that these chemicals caused polyuria and osmotic diarrhea, respectively, Na2SO4 (5-20 g/l) or NaCl (16.5 g/l) was provided to rats in drinking water. Water consumption was increased at 5- and 10-g Na2SO4/l and with NaCl. Pup weights were reduced at 20-g Na2SO4/l. Dose-related incidences and severity of polyuria and diarrhea occurred in Na2SO4-treated rats; perinasal staining was seen at 20 g/l. NaCl caused polyuria and perinasal staining, but not diarrhea. Subsequently, water was concentrated ∼120-fold and sulfate levels were reduced by barium hydroxide before chlorination, yielding lower sodium (≤1.5 g/l) and sulfate (≤2.1 g/l) levels. Treatment resulted in increased water consumption, but pup weight and survival were unaffected. There were no treatment-related clinical findings, indicating that mixtures produced by the second method are suitable for multigenerational testing.

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.

Per- and polyfluoroalkyl substances in the environment.

Over the past several years, the term PFAS (per- and polyfluoroalkyl substances) has grown to be emblematic of environmental contamination, garnering public, scientific, and regulatory concern. PFAS are synthesized by two processes, direct fluorination (e.g., electrochemical fluorination) and oligomerization (e.g., fluorotelomerization). More than a megatonne of PFAS is produced yearly, and thousands of PFAS wind up in end-use products. Atmospheric and aqueous fugitive releases during manufacturing, use, and disposal have resulted in the global distribution of these compounds. Volatile PFAS facilitate long-range transport, commonly followed by complex transformation schemes to recalcitrant terminal PFAS, which do not degrade under environmental conditions and thus migrate through the environment and accumulate in biota through multiple pathways. Efforts to remediate PFAS-contaminated matrices still are in their infancy, with much current research targeting drinking water.

Estimating costs for nitrate and perchlorate treatment for small drinking water systems.

When choosing a treatment technology for nitrate or perchlorate removal, drinking water utilities overwhelmingly choose ion exchange. However, of late, biological treatment and point-of-use systems have received a great deal of attention. This article utilizes several new U.S. Environmental Protection Agency models to estimate the cost of nitrate and perchlorate treatment for small drinking water systems. The analysis here shows that, when comparing the three technologies for a typical set of design choices and drinking water quality conditions, the least-cost option varies among the three depending on system size. This relationship varies with changes to the water quality and design factors such as, but not restricted to, influent nitrate and perchlorate concentrations, the choice of residual management options, and the presence of co-contaminants and competing ions.

Avoiding pitfalls when modeling removal of per- and polyfluoroalkyl substances by anion exchange.

Per- and polyfluoroalkyl substances (PFAS) are receiving a great deal of attention from regulators, water utilities, and the general public. Anion-exchange resins have shown high capacities for removal of these substances from water, but there is currently a paucity of ion-exchange treatment models available to evaluate performance. In this work, important theoretical and practical considerations are discussed for modeling PFAS removal from drinking water using gel-type, strong-base anion-exchange resin in batch and column processes. Several important limitations found in the literature preclude movement toward model development, including the use of inappropriate isotherms, inappropriate kinetic assumptions, and experimental conditions that are not relevant to drinking water conditions. Theoretical considerations based on ion-exchange fundamentals are presented that will be of assistance to future researchers in developing models, designing batch and column experiments, and interpreting results of batch and column experiments.

Managing and treating per- and polyfluoroalkyl substances (PFAS) in membrane concentrates.

Per- and polyfluoroalkyl substances (PFAS), which are present in many waters, have detrimental impacts on human health and the environment. Reverse osmosis (RO) and nanofiltration (NF) have shown excellent PFAS separation performance in water treatment; however, these membrane systems do not destroy PFAS but produce concentrated residual streams that need to be managed. Complete destruction of PFAS in RO and NF concentrate streams is ideal, but long-term sequestration strategies are also employed. Because no single technology is adequate for all situations, a range of processes are reviewed here that hold promise as components of treatment schemes for PFAS-laden membrane system concentrates. Attention is also given to relevant concentration processes because it is beneficial to reduce concentrate volume prior to PFAS destruction or sequestration. Given the costs and challenges of managing PFAS in membrane concentrates, it is critical to evaluate both established and emerging technologies in selecting processes for immediate use and continued research.

Concentration, chlorination, and chemical analysis of drinking water for disinfection byproduct mixtures health effects research: U.S. EPA's Four Lab Study.

The U.S. Environmental Protection Agency's "Four Lab Study" involved participation of researchers from four national Laboratories and Centers of the Office of Research and Development along with collaborators from the water industry and academia. The study evaluated toxicological effects of complex disinfection byproduct (DBP) mixtures, with an emphasis on reproductive and developmental effects that have been associated with DBP exposures in some human epidemiologic studies. This paper describes a new procedure for producing chlorinated drinking water concentrate for animal toxicology experiments, comprehensive identification of >100 DBPs, and quantification of 75 priority and regulated DBPs. In the research reported herein, complex mixtures of DBPs were produced by concentrating a natural source water with reverse osmosis membranes, followed by addition of bromide and treatment with chlorine. By concentrating natural organic matter in the source water first and disinfecting with chlorine afterward, DBPs (including volatiles and semivolatiles) were formed and maintained in a water matrix suitable for animal studies. DBP levels in the chlorinated concentrate compared well to those from EPA's Information Collection Rule (ICR) and a nationwide study of priority unregulated DBPs when normalized by total organic carbon (TOC). DBPs were relatively stable over the course of the animal studies (125 days) with multiple chlorination events (every 5-14 days), and a significant portion of total organic halogen was accounted for through a comprehensive identification approach. DBPs quantified included regulated DBPs, priority unregulated DBPs, and additional DBPs targeted by the ICR. Many DBPs are reported for the first time, including previously undetected and unreported haloacids and haloamides. The new concentration procedure not only produced a concentrated drinking water suitable for animal experiments, but also provided a greater TOC concentration factor (136×), enhancing the detection of trace DBPs that are often below detection using conventional approaches.

The impact of temperature on the performance of anaerobic biological treatment of perchlorate in drinking water.

A 20-month pilot-scale study was conducted to examine the impact of temperature on the performance of an anaerobic biological contractor used to treat perchlorate-contaminated water. The contractor was successfully acclimated with indigenous microorganisms. Influent temperatures varied from 1.4 to 30 degrees C. The objectives of the study were to investigate the effects of temperature on perchlorate removal, nitrate removal, nitrite formation, dissolved oxygen consumption, sulfide production, and nutrient acetate consumption. The results confirmed that consistent biological perchlorate removal to 2 microg /L is feasible at temperatures above 10 degrees C. Effluent concentrations of perchlorate, nitrate, and dissolved oxygen varied inversely with temperature, while sulfide varied positively with temperature. Under the conditions that prevailed during this study, 10 degrees C was a threshold temperature below which microbial activity, including perchlorate reduction, decreased dramatically.

Integrated disinfection by-products mixtures research: concentration by reverse osmosis membrane techniques of disinfection by-products from water disinfected by chlorination and ozonation/postchlorination.

To conduct the health-effect studies described in subsequent articles in this series, concentrated aqueous mixtures of disinfection by-products were required for the two water treatment trains described in the preceding article (Miltner et al., 2008). To accomplish this, the finished drinking waters from each treatment train were sent through cation-exchange resin columns to remove hardness and free chlorine. Reverse osmosis membranes were then used to concentrate approximately 2400 L of each finished water down to approximately 18 L. The resulting volumetric concentration factors for the chlorinated and ozonated/postchlorinated waters were 136- and 124-fold, respectively. The concentrates were spiked with select disinfection by-products (DBPs) that were lost during the concentration effort. The results, along with the rationale for choosing the method of concentration, are presented. After reintroduction of a select list of lost DBPs, the concentration methodology used herein was able to produce concentrates that retained large percentages of the DBPs that were in the initial finished drinking waters. Further, the distributions of the DBPs in the concentrates matched those found in the finished drinking waters.

Integrated disinfection by-products mixtures research: disinfection of drinking waters by chlorination and ozonation/postchlorination treatment scenarios.

This article describes disinfection of the same source water by two commonly used disinfection treatment scenarios for purposes of subsequent concentration, chemical analysis, and toxicological evaluation. Accompanying articles in this issue of the Journal of Toxicology and Environmental Health describe concentration of these finished waters by reverse osmosis techniques, chemical characterization of the resulting disinfection by-product (DBP) concentrates, in vivo and in vitro toxicological results, and risk assessment methods developed to analyze data from this project. This project, called the "Four Lab Study," involved participation of scientists from four laboratories/centers of the U.S. Environmental Protection Agency Office of Research and Development as well as extramural collaborators from the water industry and academia. One of the two finished waters was prepared by conventional treatment and disinfected by chlorination. The other finished water was also prepared by conventional treatment and disinfected by ozonation followed by chlorination (ozonation/postchlorination). Chlorination conditions of dose, time and temperature were similar for both treatment scenarios, allowing for a comparison. Both finished waters had acceptably low levels of particulates and bacteria, representative pH and chlorine levels, and contained numerous DBP. Known effects of ozonation were observed in that, relative to the water that was chlorinated only, the ozonated/postchlorinated water had lower concentrations of total organic halogen, trihalomethanes (THM), haloacetic acids (HAA), and higher concentrations of bromate, and aldehydes.

Research issues underlying the four-lab study: integrated disinfection by-products mixtures research.

Chemical disinfection of drinking water is a major public health triumph of the 20th century, resulting in significant decreases in morbidity and mortality from waterborne diseases. Disinfection by-products (DBP) are chemicals formed by the reaction of oxidizing disinfectants with inorganic and organic materials in the source water. To address potential health concerns that cannot be answered directly by toxicological research on individual DBPs or defined DBP mixtures, scientists residing within the various organizations of the U.S. Environmental Protection Agency's Office of Research and Development (the National Health and Environmental Effects Research Laboratory, the National Risk Management Research Laboratory, the National Exposure Research Laboratory, and the National Center for Environmental Assessment) engaged in joint investigation of environmentally realistic complex mixtures of DBP. Research on complex mixtures of DBP is motivated by three factors: (a) DBP exposure is ubiquitous to all segments of the population; (b) some positive epidemiologic studies are suggestive of potential developmental, reproductive, or carcinogenic health effects in humans exposed to DBP; and (c) significant amounts of the material that makes up the total organic halide portion of the DBP have not been identified. The goal of the Integrated Disinfection Byproducts Mixtures Research Project (the 4Lab Study) is provision of sound, defensible, experimental data on environmentally relevant mixtures of DBP and an improved estimation of the potential health risks associated with exposure to the mixtures of DBP formed during disinfection of drinking water. A phased research plan was developed and implemented. The present series of articles provides the results from the first series of experiments.

Integrated disinfection by-products research: assessing reproductive and developmental risks posed by complex disinfection by-product mixtures.

This article presents a toxicologically-based risk assessment strategy for identifying the individual components or fractions of a complex mixture that are associated with its toxicity. The strategy relies on conventional component-based mixtures risk approaches such as dose addition, response addition, and analyses of interactions. Developmental toxicity data from two drinking-water concentrates containing disinfection by-products (DBP) mixtures were used to illustrate the strategy. The results of this study showed that future studies of DBP concentrates using the Chernoff-Kavlock bioassay need to consider evaluating DBP that are concentrated more than 130-fold and using a rat strain that is more sensitive to chemically-induced pregnancy loss than Sprague-Dawley rats. The results support the planned experimental design of a multigeneration reproductive and developmental study of DBP concentrates. Finally, this article discusses the need for a systematic evaluation of DBP concentrates obtained from multiple source waters and treatment types. The development of such a database could be useful in evaluating whether a specific DBP concentrate is sufficiently similar to tested combinations of source waters and treatment alternatives so that health risks for the former may be estimated using data on the latter.