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•SPAC had up to s480 times higher adsorption mass loading of PFAAs than GAC.•SPAC and GAC adsorption efficiency depends on PFAS chain length.•The ceramic MF membrane had minimal ...fouling during long-term filtration.•PFASs were effectively removed by the combined SPAC/MF system.
Contamination of drinking water sources with per- and polyfluoroalkyl substances (PFASs) is a major challenge for environmental engineers. While granular activated carbon (GAC) is an effective adsorbent-based treatment technology for long-chained PFASs, GAC is less effective for removal of short-chained compounds, necessitating a more complete treatment strategy. Super-fine powder activated carbon (SPAC; particle diameter <1 um) is potentially a superior adsorbent to GAC due to high specific surface area and faster adsorption kinetics. This study served to evaluate SPAC coupled with ceramic microfiltration (CMF) for PFAS removal in a continuous flow system. Comparison of PFAS mass loading rates onto SPAC and GAC to 10% breakthrough of PFASs using contaminated groundwater indicates that SPAC has nearly double the adsorption potential of GAC. Limitations reaching breakthrough for the SPAC system led to additional higher mass loading experiments where PFAS adsorption onto SPAC reached 2990 μg/g (for quantifiable PFASs), 480x greater than GAC and is thought to be a function of adsorbent size, pore content and PFAS chain length. Additional analysis of system performance through the application of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) revealed the presence of additional PFASs in influent samples that were removed by the SPAC/CMF system.
A process based on electrical discharge plasma was tested for the transformation of perfluorooctanoic acid (PFOA). The plasma-based process was adapted for two cases, high removal rate and high ...removal efficiency. During a 30 min treatment, the PFOA concentration in 1.4 L of aqueous solutions was reduced by 90% with the high rate process (76.5 W input power) and 25% with the high efficiency process (4.1 W input power). Both achieved remarkably high PFOA removal and defluorination efficiencies compared to leading alternative technologies. The high efficiency process was also used to treat groundwater containing PFOA and several cocontaminants including perfluorooctanesulfonate (PFOS), demonstrating that the process was not significantly affected by cocontaminants and that the process was capable of rapidly degrading PFOS. Preliminary investigation into the byproducts showed that only about 10% of PFOA and PFOS is converted into shorter-chain perfluoroalkyl acids (PFAAs). Investigation into the types of reactive species involved in primary reactions with PFOA showed that hydroxyl and superoxide radicals, which are typically the primary plasma-derived reactive species, play no significant role. Instead, scavenger experiments indicated that aqueous electrons account for a sizable fraction of the transformation, with free electrons and/or argon ions proposed to account for the remainder.
Desalination of unconventional water resources is becoming increasingly common for the augmentation of drinking water supplies. Desalination is energy and cost intensive, and concentrate disposal is ...a significant issue that impedes desalination in many regions of the globe. One possible approach to decrease desalination costs while alleviating concentrate disposal issues is through the extraction of valuable commodities. While past researchers have evaluated the technical feasibility of extracting minerals from both seawater and, to a lesser extent, desalination concentrate, the feasibility of commodity extraction is dependent upon technical, energy, and cost considerations, as well as, market fluctuations of the minerals extracted. Most of the available literature has focused on technical processes used to extract minerals and has not evaluated the feasibility of extraction considering the aforementioned concerns. For this study, the feasibility of material extraction from seawater and desalination concentrate was investigated through three steps: 1) screening for potentially profitable compounds; 2) reviewing literature on extraction methods and market fluctuations for these compounds; and 3) assessing the costs of extracting these compounds. Although the extraction of various compounds from desalination concentrate is technically viable, based on the literature review and the primarily cost analysis, the extraction of the majority would not be profitable considering the current market and available technologies. The results from this study suggest that while the extraction of commodities of sodium, chlorine, potassium, and magnesium from desalination concentrate could be profitable, the feasibility of extraction is highly dependent on commodity pricing and final product purity. Due to the marginally attractive economics of extraction and significant uncertainties associated with producing commodities, this study suggests that extraction from desalination concentrate is unlikely to significantly improve the economics of desalination unless concentrate disposal costs were significantly reduced as a result.
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•Extraction from desalination concentrate is dependent upon numerous factors.•If high purity products could be produced, extraction of major ions is feasible.•Extraction of trace metals is currently economically unfeasible.
•Basic guidelines for plasma reactor design and optimization have been developed.•Rhodamine B degradation depends on the area of the plasma–liquid interface.•Reactor performance can be improved by ...generating foam on the liquid surface.
To improve the feasibility of plasma-based water treatment technology and develop basic guidelines for reactor design and optimization, a study was conducted to identify and characterize design parameters and physical phenomena that influence treatment efficiency. The first phase of the study established that the chemical reactions responsible for the degradation of organic solutes can be more accurately represented, mathematically, as heterogeneous reactions, rather than the common representation as homogeneous reactions. Using Rhodamine B as the model solute, the observed removal rate constant was found to be proportional to the area of the plasma–liquid interface. This observation supported the validity of the proposed heterogeneous rate equation and inspired the conception of a general design principle, which prescribes maximizing contact between the plasma and the treated solution. The second phase of the study involved the application of this design principle to create seven different “contact-oriented” reactors. The design parameters employed to increase contact included feeding liquid streams directly through the discharge region and generating a layer of foam on the liquid surface. The contact-oriented reactors validated their founding principle by achieving removal efficiencies up to 145 times that for the reference case (point-plate with discharge in liquid). The removal efficiencies attained in this work compare quite favorably with those achieved by other advanced oxidation processes for the degradation of Rhodamine B.
Conventional water resources in many regions are insufficient to meet the water needs of growing populations, thus reuse is gaining acceptance as a method of water supply augmentation. Recent ...advancements in membrane technology have allowed for the reclamation of municipal wastewater for the production of drinking water, i.e., potable reuse. Although public perception can be a challenge, potable reuse is often the least energy-intensive method of providing additional drinking water to water stressed regions. A variety of membranes have been developed that can remove water contaminants ranging from particles and pathogens to dissolved organic compounds and salts. Typically, potable reuse treatment plants use polymeric membranes for microfiltration or ultrafiltration in conjunction with reverse osmosis and, in some cases, nanofiltration. Membrane properties, including pore size, wettability, surface charge, roughness, thermal resistance, chemical stability, permeability, thickness and mechanical strength, vary between membranes and applications. Advancements in membrane technology including new membrane materials, coatings, and manufacturing methods, as well as emerging membrane processes such as membrane bioreactors, electrodialysis, and forward osmosis have been developed to improve selectivity, energy consumption, fouling resistance, and/or capital cost. The purpose of this review is to provide a comprehensive summary of the role of polymeric membranes and process components in the treatment of wastewater to potable water quality and to highlight recent advancements and needs in separation processes. Beyond membranes themselves, this review covers the background and history of potable reuse, and commonly used potable reuse process chains, pretreatment steps, and advanced oxidation processes. Key trends in membrane technology include novel configurations, materials, and fouling prevention techniques. Challenges still facing membrane-based potable reuse applications, including chemical and biological contaminant removal, membrane fouling, and public perception, are highlighted as areas in need of further research and development.
This study investigated membrane fouling during wastewater reclamation by collecting operational performance data and employing state-of-the-art techniques for characterization of membrane foulants. ...Utilizing a pilot-scale membrane unit, two nanofiltration membranes (NF-90 and NF-4040, Dow/Filmtec) and one low-pressure reverse osmosis membrane (TMG10, Toray America) were tested at two wastewater reclamation facilities treating microfiltered non-nitrified secondary effluent and nitrified/denitrified tertiary effluent. The membranes and foulants were characterized by environmental scanning electron microscopy coupled with energy dispersive spectroscopy, attenuated total reflection-Fourier transform infrared spectrometry, zeta-potential measurement, atomic force microscopy, phospholipids analysis, and contact angle measurement.
During treatment of the nitrified/denitrified effluent, membrane fouling was dominated by biofouling in combination with organic fouling, colloidal fouling, and inorganic scaling. Sufficient chloramines residual was identified as being critical in controlling biofouling during wastewater desalination. During filtration of the non-nitrified effluent, fouling of the membrane lead-elements was mainly caused by adsorption and deposition of effluent organic matter while biofouling still observed in tail-elements despite the formation of chloramines. Rough and hydrophobic membrane with high permeability (e.g., NF-90) displayed more severe initial specific flux decline during filtration, while smooth and hydrophilic membrane (e.g., NF-4040) exhibited high and constant specific flux when biofouling was under control.
•Removal of perfluoroalkyl acids by GAC and NF was evaluated.•Virgin and fouled NF270 membranes were tested using artificial groundwater.•Multiple carbons tested using rapid small scale column tests ...with and without DOM.•NF270 had >93% removal of all PFAAs during all experiments.•Carbon performance varied based on type, water chemistry, and sorbate.
Perfluoroalkyl acids (PFAAs) are of concern because of their persistence in the environment and the potential toxicological effects on humans exposed to PFAAs through a variety of possible exposure routes, including contaminated drinking water. This study evaluated the efficacy of nanofiltration (NF) and granular activated carbon (GAC) adsorption in removing a suite of PFAAs from water. Virgin flat-sheet NF membranes (NF270, Dow/Filmtec) were tested at permeate fluxes of 17–75Lm−2h−1 using deionized (DI) water and artificial groundwater. The effects of membrane fouling by humic acid on PFAA rejection were also tested under constant permeate flux conditions. Both virgin and fouled NF270 membranes demonstrated >93% removal for all PFAAs under all conditions tested. GAC efficacy was tested using rapid small-scale columns packed with Calgon Filtrasorb®300 (F300) carbon and DI water with and without dissolved organic matter (DOM). DOM effects were also evaluated with F600 and Siemens AquaCarb®1240C. The F300 GAC had <20% breakthrough of all PFAAs in DI water for up to 125,000 bed volumes (BVs). When DOM was present, >20% breakthrough of all PFAAs by 10,000 BVs was observed for all carbons.
The incomplete rejection of certain pesticides, disinfection by-products, endocrine disrupting compounds, and pharmaceutically active compounds has been reported during full- and pilot-scale ...high-pressure membrane applications. Since the removal of these compounds in water and wastewater treatment applications is of great importance where a high product water quality is desired, an understanding of the factors affecting the permeation of solutes in high-pressure membrane systems is needed. In this paper, findings of a comprehensive literature review are reported, targeting membrane rejection mechanisms and factors affecting rejection. The following key solute parameters were identified to primarily affect solute rejection: molecular weight (MW), molecular size (length and width), acid disassociation constant (p
K
a), hydrophobicity/hydrophilicity (log
K
ow), and diffusion coefficient (
D
p). Key membrane properties affecting rejection that were identified include molecular weight cut-off, pore size, surface charge (measured as zeta potential), hydrophobicity/hydrophilicity (measured as contact angle), and surface morphology (measured as roughness). In addition, feed water composition, such as pH, ionic strength, hardness, and the presence of organic matter, was also identified as having an influence on solute rejection. From the knowledge gained during the literature review, a rejection diagram was proposed, which qualitatively allows prediction of solute rejection if certain solute and membrane properties are known.
Commercial polyamide nanofiltration (NF), reverse osmosis (RO), and ultra-low pressure RO (ULPRO) membranes (NF-90, NF-200, TFC-HR, and XLE) as well as a cellulose triacetate RO membrane (CTA) were ...employed to investigate the effect of fouling on transport of organic micropollutants. Due to foulant precipitation and cake-layer formation, membrane surface characteristics changed considerably in terms of contact angle (an index of hydrophobicity), zeta-potential, functionality, and surface morphology, which potentially affected transport of contaminants as compared to unfouled (virgin) membranes. The transport of ionic organic micropollutants was hindered as a result of improved Donnan exclusion (electrostatic repulsion) likely due to a more negative surface charge as quantified by zeta-potential measurements. Membrane fouling also resulted in an increased adsorption capacity and reduced mass transport through partitioning and diffusion of solutes across the membrane. These effects led to an increase in rejection of hydrophobic non-ionic solutes (e.g., disinfection byproducts and chlorinated solvents) by fouled membranes. However, the increasing surface charge has the potential to result in a larger molecular weight cut-off of a fouled membrane due to membrane swelling, which can lead to lower rejection for hydrophilic non-ionic solutes, especially where nanofiltration membranes with a larger molecular weight cut-off are employed. Membrane fouling facilitated the transport of hydrophobic and hydrophilic organic contaminants through CTA membranes resulting in elevated concentrations of target solutes in the permeate. Findings of the study indicate that membrane fouling significantly affects the rejection of organic solute by CTA, NF, and ULPRO membranes while it is less important for thin film composite RO membranes.
•Nanofiltration experiments were performed with 67 nonionic organic compounds.•QSPR models were developed to predict the rejection of compounds by a nanofiltration (NF) membrane.•Two types of models ...(QSPR-Spiegler–Kedem models and QSPRs using flux as a variable) were developed.•Developed linear and nonlinear models can be used to predict the rejection over a wide range of flux.•Developed models are applicable only to nonionic organic compounds without membrane affinity.
Recent interest in quantitative structure property/activity relationship (QSPR/QSAR) models to predict the removal of organic contaminants by membrane processes has highlighted the need to develop models applicable to different operating conditions, such as flux. In this study, two types of QSPR models were developed to predict removal of nonionic organic compounds by a nanofiltration membrane (NF270) including: (1) QSPR models with flux as an independent (or predictor) variable; and (2) QSPR models to predict fitting parameters of a fundamental model (i.e., Spiegler–Kedem model). Rejection data for 67 nonionic organic compounds and an NF membrane at five solvent fluxes (10–120Lm−2h−1) were generated and used for model development and validation. In order to select the best statistical method to develop QSPRs, several models were developed using multiple linear regression (MLR), partial least squares (PLS), and artificial neural network (ANN) with molecular descriptors selected by different methods (i.e., filtering, hybrid, and wrapper methods). The most effective linear and nonlinear models were developed using PLS and ANN with molecular descriptors selected by variable importance plot and feed forward selection. The rejection of nonionic compounds with minimal solute-membrane affinity could be described by permeate flux, and a compound’s molecular depth and diffusion coefficient. Fitting parameters of Spiegler–Kedem model (reflection coefficient and permeability coefficient) could be best described by size parameters and diffusivity. These results indicate that the rejection of the majority of the nonionic organic compounds evaluated was mainly due to size exclusion. Generally, both QSPR methods developed during this study were found to be effective methods for predicting solute rejection by the nanofiltration membrane, and nonlinear models provided better fits (based on statistical parameters) of both training and validation rejection datasets.
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