Machine Learning for Polymer Design to Enhance Pervaporation-Based Organic Recovery.

Pervaporation (PV) is an effective membrane separation process for organic dehydration, recovery, and upgrading. However, it is crucial to improve membrane materials beyond the current permeability-selectivity trade-off. In this research, we introduce machine learning (ML) models to identify high-potential polymers, greatly improving the efficiency and reducing cost compared to conventional trial-and-error approach. We utilized the largest PV data set to date and incorporated polymer fingerprints and features, including membrane structure, operating conditions, and solute properties. Dimensionality reduction, missing data treatment, seed randomness, and data leakage management were employed to ensure model robustness. The optimized LightGBM models achieved RMSE of 0.447 and 0.360 for separation factor and total flux, respectively (logarithmic scale). Screening approximately 1 million hypothetical polymers with ML models resulted in identifying polymers with a predicted permeation separation index >30 and synthetic accessibility score <3.7 for acetic acid extraction. This study demonstrates the promise of ML to accelerate tailored membrane designs.

Electrolytic Seawater Mineralization and the Mass Balances That Demonstrate Carbon Dioxide Removal.

We present the mass balances associated with carbon dioxide (CO2) removal (CDR) using seawater as both the source of reactants and as the reaction medium via electrolysis following the "Equatic" (formerly known as "SeaChange") process. This process, extensively detailed in La Plante E.C.; ACS Sustain. Chem. Eng.2021, 9, ( (3), ), 1073-1089, involves the application of an electric overpotential that splits water to form H+ and OH- ions, producing acidity and alkalinity, i.e., in addition to gaseous coproducts, at the anode and cathode, respectively. The alkalinity that results, i.e., via the "continuous electrolytic pH pump" results in the instantaneous precipitation of calcium carbonate (CaCO3), hydrated magnesium carbonates (e.g., nesquehonite: MgCO3·3H2O, hydromagnesite: Mg5(CO3)4(OH)2·4H2O, etc.), and/or magnesium hydroxide (Mg(OH)2) depending on the CO32- ion-activity in solution. This results in the trapping and, hence, durable and permanent (at least ∼10 000-100 000 years) immobilization of CO2 that was originally dissolved in water, and that is additionally drawn down from the atmosphere within: (a) mineral carbonates, and/or (b) as solvated bicarbonate (HCO3-) and carbonate (CO32-) ions (i.e., due to the absorption of atmospheric CO2 into seawater having enhanced alkalinity). Taken together, these actions result in the net removal of ∼4.6 kg of CO2 per m3 of seawater catholyte processed. Geochemical simulations quantify the extents of net CO2 removal including the dependencies on the process configuration. It is furthermore indicated that the efficiency of realkalinization of the acidic anolyte using alkaline solids depends on their acid neutralization capacity and dissolution reactivity. We also assess changes in seawater chemistry resulting from Mg(OH)2 dissolution with emphasis on the change in seawater alkalinity and saturation state. Overall, this analysis provides direct quantifications of the ability of the Equatic process to serve as a means for technological CDR to mitigate the worst effects of accelerating climate change.

Simple and Low-Cost Electroactive Membranes for Ammonia Recovery.

Ammonia is considered a contaminant to be removed from wastewater. However, ammonia is a valuable commodity chemical used as the primary feedstock for fertilizer manufacturing. Here we describe a simple and low-cost ammonia gas stripping membrane capable of recovering ammonia from wastewater. The material is composed of an electrically conducting porous carbon cloth coupled to a porous hydrophobic polypropylene support, that together form an electrically conductive membrane (ECM). When a cathodic potential is applied to the ECM surface, hydroxide ions are produced at the water-ECM interface, which transforms ammonium ions into higher-volatility ammonia that is stripped across the hydrophobic membrane material using an acid-stripping solution. The simple structure, low cost, and easy fabrication process make the ECM an attractive material for ammonia recovery from dilute aqueous streams, such as wastewater. When paired with an anode and immersed into a reactor containing synthetic wastewater (with an acid-stripping solution providing the driving force for ammonia transport), the ECM achieved an ammonia flux of 141.3 ± 14.0 g.cm-2.day-1 at a current density of 6.25 mA.cm-2 (69.2 ± 5.3 kg(NH3-N)/kWh). It was found that the ammonia flux was sensitive to the current density and acid circulation rate.

High-Efficiency Recovery of Acetic Acid from Water Using Electroactive Gas-Stripping Membranes.

Recovery of carbon-based resources from waste is a critical need for achieving carbon neutrality and reducing fossil carbon extraction. We demonstrate a new approach for extracting volatile fatty acids (VFAs) using a multifunctional direct heated and pH swing membrane contactor. The membrane is a multilayer laminate composed of a carbon fiber (CF) bound to a hydrophobic membrane and sealed with a layer of polydimethylsiloxane (PDMS); this CF is used as a resistive heater to provide a thermal driving force for PDMS that, while a highly hydrophobic material, is known for its ability to rapidly pass gases, including water vapor. The transport mechanism for gas transport involves the diffusion of molecules through the free volume of the polymer matrix. CF coated with polyaniline (PANI) is used as an anode to induce an acidic pH swing at the interface between the membrane and water, which can protonate the VFA molecule. The innovative multilayer membrane used in this study has successfully demonstrated a highly efficient recovery of VFAs by simultaneously combining pH swing and joule heating. This novel technique has revealed a new concept in the field of VFA recovery, offering promising prospects for further advancements in this area. The energy consumption was 3.37 kWh/kg for acetic acid (AA), and an excellent separation factor of AA/water of 51.55 ± 2.11 was obtained with high AA fluxes of 51.00 ± 0.82 g.m-2hr-1. The interfacial electrochemical reactions enable the extraction of VFAs without the need for bulk temperature and pH modification.

Electrolytic Sulfuric Acid Production with Carbon Mineralization for Permanent Carbon Dioxide Removal.

Several billion metric tons per year of durable carbon dioxide removal (CDR) will be needed by mid-century to prevent catastrophic climate warming, and many new approaches must be rapidly scaled to ensure this target is met. Geologically permanent sequestration of carbon dioxide (CO2) in carbonate minerals-carbon mineralization-requires two moles of alkalinity and one mole of a CO2-reactive metal such as calcium or magnesium per mole of CO2 captured. Chemical weathering of geological materials can supply both ingredients, but weathering reactions must be accelerated to achieve targets for durable CDR. Here, a scalable CDR and mineralization process is reported in which water electrolysis is used to produce sulfuric acid for accelerated weathering, while a base is used to permanently sequester CO2 from air into carbonate minerals. The process can be integrated into existing extractive processes by reacting produced sulfuric acid with critical element feedstocks that neutralize acidity (e.g., rock phosphorus or ultramafic rock mine tailings), with calcium- and magnesium-bearing sulfate wastes electrolytically upcycled. The highest reported efficiency of electrolytic sulfuric acid production is achieved by maintaining catholyte feed conditions that minimize Faradaic losses by hydroxide permeation of the membrane-separated electrochemical cell. The industrial implementation of this process provides a pathway to gigaton-scale CO2 removal and sequestration during the production of critical elements needed for decarbonizing global energy infrastructure and feeding the world.

Multistage Surface-Heated Vacuum Membrane Distillation Process Enables High Water Recovery and Excellent Heat Utilization: A Modeling Study.

Surface-heated membrane distillation (MD) enhances the energy efficiency of desalination by mitigating temperature polarization (TP). However, systematic investigations of larger scale, multistage, surface-heated MD system with high water recovery and heat recycling are limited. Here, we explore the design and performance of a multistage surface-heated vacuum MD (SHVMD) with heat recovery through a comprehensive finite difference model. In this process, the latent heat of condensation is recovered through an internal heat exchanger (HX) using the retentate from one stage as the condensing fluid for the next stage and an external HX using the feed as the condensing fluid. Model results show that surface heating enhances the performance compared to conventional vacuum MD (VMD). Specifically, in a six-stage SHVMD process, 54.44% water recovery and a gained output ratio (GOR) of 3.28 are achieved with a surface heat density of 2000 W m-2, whereas a similar six-stage VMD process only reaches 18.19% water recovery and a GOR of 2.15. Mass and energy balances suggest that by mitigating TP, surface heating increases the latent heat trapped in vapor. The internal and external HXs capture and reuse the additional heat, which enhances the GOR values. We show for SHVMD that the hybrid internal/external heat recovery design can have GOR value 1.44 times higher than that of systems with only internal or external heat recovery. Furthermore, by only increasing six stages to eight stages, a GOR value as high as 4.35 is achieved. The results further show that surface heating can reduce the energy consumption of MD for brine concentration. The multistage SHVMD technology exhibits a promising potential for the management of brine from industrial plants.

A reverse-selective ion exchange membrane for the selective transport of phosphates via an outer-sphere complexation-diffusion pathway.

Specific-ion selectivity is a highly desirable feature for the next generation of membranes. However, existing membranes rely on differences in charge, size and hydration energy, which limits their ability to target individual ion species. Here we demonstrate a nanocomposite ion-exchange membrane material that enables a reverse-selective transport mechanism that can selectively pass a single ion species. We demonstrate this transport mechanism with phosphate ions selectively transporting across negatively charged cation exchange membranes. Selective transport is enabled by the in situ growth of hydrous manganese oxide nanoparticles throughout a cation exchange membrane that provide a diffusion pathway via phosphate-specific, reversible outer-sphere interactions. On incorporating the hydrous manganese oxide nanoparticles, the membrane's phosphate flux increased by a factor of 27 over an unmodified cation exchange membrane, and the selectivity of phosphorous over sulfate, nitrate and chloride reaches 47, 100 and 20, respectively. By pairing ion-specific outer-sphere interactions between the target ions and appropriate nanoparticles, these nanocomposite ion-exchange materials can, in principle, achieve selective transport for a range of ions.

Desalinating a real hyper-saline pre-treated produced water via direct-heat vacuum membrane distillation.

Membrane distillation (MD) is an emerging thermal desalination technology capable of desalinating waters of any salinity. During typical MD processes, the saline feedwater is heated and acts as the thermal energy carrier; however, temperature polarization (as well as thermal energy loss) contributes to low distillate fluxes, low single-pass water recovery and poor thermal efficiency. An alternative approach is to integrate an extra thermal energy carrier as part of the membrane and/or module assembly, which can channel externally provided heat directly to the membrane-feedwater interface and/or along the feed channel length. This direct-heat delivery has been demonstrated to increase single-pass water recovery and enhance the overall thermal efficiency. We developed a bench-scale direct-heated vacuum MD (DHVMD) process to desalinate pre-treated oil and gas "produced water" with an initial total dissolved solids of 115,500 ppm at a feed temperature ranging between 24 and 32 °C. We evaluated both water flux and specific energy consumption (SEC) as a function of water recovery. The system achieved a 50% water recovery without significant scaling, with an average flux >6 kg m-2 hr-1 and a SEC as low as 2,530 kJ kg-1. The major species of mineral scales (i.e., NaCl, CaSO4, and SrSO4) that limited the water recovery to 68% were modeled in terms of thermodynamics and identified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. In addition, we further developed and employed a physics-based process model to estimate temperature, salinity, water transport and energy flows for full-scale vacuum MD and DHVMD modules. Model results show that a direct-heat input rate of 3,600 W can increase single-pass water recovery from 2.1% to 3.1% while lowering the thermal SEC from 7,800 kJ kg-1 to 6,517 kJ kg-1 in an unoptimized module. Finally, the scaling up potential of DHVMD process is briefly discussed.

Multiplexed Anodic Stripping Voltammetry Detection of Heavy Metals in Water Using Nanocomposites Modified Screen-Printed Electrodes Integrated With a 3D-Printed Flow Cell.

In this study, we present multiplexed anodic stripping voltammetry (ASV) detection of heavy metal ions (HMIs)-As(III), Cd(II), and Pb(II)-using a homemade electrochemical cell consisting of dual working, reference and counter screen-printed electrodes (SPE) on polyimide substrate integrated with a 3D-printed flow cell. Working and counter electrodes were fabricated by the screen-printing of graphite paste while the Ag/AgCl paste was screen-printed as a reference electrode (Ag/AgCl quasi-reference electrode). The working electrodes were modified with (BiO)2CO3-reduced graphene oxide (rGO)-Nafion [(BiO)2CO3-rGO-Nafion] and Fe3O4 magnetic nanoparticles (Fe3O4MNPs) decorated Au nanoparticles (AuNPs)-ionic liquid (IL) (Fe3O4-Au-IL) nanocomposites separately to enhance HMIs sensing. Electrochemical detection was achieved using square wave ASV technique. The desired structure of the flow electrochemical cell was optimized by the computational fluid dynamic (CFD). Different experimental parameters for stripping analysis of HMIs were optimized including deposition time, deposition potential and flow rate. The linear range of calibration curves with the sensing nanocomposites modified SPE for the three metal ions was from 0-50 µg/L. The limits of detection (S/N = 3) were estimated to be 2.4 µg/L for As(III), 1.2 µg/L for Pb(II) and 0.8 µg/L for Cd(II). Furthermore, the homemade flow anodic stripping sensor platform was used to detect HMIs in simulated river water with a 95-101% recovery, indicating high selectivity and accuracy and great potential for applicability even in complex matrices.

Enhanced removal of per- and polyfluoroalkyl substances in complex matrices by polyDADMAC-coated regenerable granular activated carbon.

Granular activated carbon (GAC) has been used to remove per- and polyfluoroalkyl substances (PFASs) from industrial or AFFF-impacted waters, but its effectiveness can be low because adsorption of short-chained PFASs is ineffective and its sites are exhausted rapidly by co-contaminants. To increase adsorption of anionic PFASs on GAC by electrostatic attractions, we modified GAC's surface with the cationic polymer poly diallyldimethylammonium chloride (polyDADMAC) and tested its capacity in complex water matrices containing dissolved salts and humic acid. Amending with concentrations of polyDADMAC as low as 0.00025% enhanced GAC's adsorption capacity for PFASs, even in the presence of competing ions. This suggests that electrostatic interactions with polyDADMAC's quaternary ammonium functional groups helped bind organic and inorganic ions as well as the headgroup of short-chain PFASs, allowing more overall PFAS removal by GAC. Evaluating the effect of polymer dose is important because excessive addition can block pores and reduce overall PFAS removal rather than increase it. To decrease the waste associated with this adsorption strategy by making the adsorbent viable for more than one saturation cycle, a regeneration method is proposed which uses low-power ultrasound to enhance the desorption of PFASs from the polyDADMAC-GAC with minimum disruption to the adsorbent's structure. Re-modification with the polymer after sonication resulted in a negligible decrease in the sorbent's capacity over four saturation rounds. These results support consideration of polyDADMAC-modified GAC as an effective regenerable adsorbent for ex-situ concentration step of both short and long-chain PFASs from real waters with high concentrations of competing ions and low PFAS loads.

Cost-benefit analysis of nanofertilizers and nanopesticides emphasizes the need to improve the efficiency of nanoformulations for widescale adoption.

Nanotechnology-based approaches have demonstrated encouraging results for sustainable agriculture production, particularly in the field of fertilizers and pesticide innovation. It is essential to evaluate the economic and environmental benefits of these nanoformulations. Here we estimate the potential revenue gain/loss associated with nanofertilizer and/or nanopesticide use, calculate the greenhouse gas emissions change from the use of nanofertilizer and identify feasible applications and critical issues. The cost-benefit analysis demonstrates that, while current nanoformulations show promise in increasing the net revenue from crops and lowering the environmental impact, further improving the efficiency of nanoformulations is necessary for their widescale adoption. Innovating nanoformulation for targeted delivery, lowering the greenhouse gas emissions associated with nanomaterials and minimizing the content of nanomaterials in the derived nanofertilizers or pesticides can substantially improve both economic and environmental benefits.

Nitrate Removal in an Electrically Charged Granular-Activated Carbon Column.

Nitrate removal from groundwater remains a challenge. Here, we report on the development of a flow-through, electrically charged, granular-activated carbon (GAC)-filled column, which effectively removes nitrate. In this system, the GAC functioned as an anode, while a titanium sheet acted as a cathode. The high removal rate of nitrate was achieved through a combination of electrosorption and electrochemical transformation to N2. The column could be readily regenerated in situ by reversing the polarity of the applied potential. We demonstrate that in the presence of chloride, the mechanism responsible for the observed nitrate removal involves a combination of electroadsorption of nitrate to the anodically charged GAC, electroreduction of nitrate to ammonium, and the oxidation of ammonium to N2 gas by reactive chlorine and other oxidative radicals (with nearly 100% N2 selectivity). Given the ubiquitous presence of chloride in groundwater, this method represents a ready, green, and sustainable treatment process with significant potential for the remediation of contaminated groundwater.

Removal of As(III) by Electrically Conducting Ultrafiltration Membranes.

As(III) species are the predominant form of arsenic found in groundwater. However, nanofiltration (NF) and reverse osmosis (RO) membranes are often unable to effectively reject As(III). In this study, we fabricate highly conducting ultrafiltration (UF) membranes for effective As(III) rejection. These membranes consist of a hydrophilic nickel-carbon nanotubes layer deposited on a UF support, and used as cathodes. Applying cathodic potentials significantly increased As(III) rejection in synthetic/real tap water, a result of locally elevated pH that is brought upon through water electrolysis at the membrane/water interface. The elevated pH conditions convert H3ASO3 to H2AsO3-/HAsO32- that are rejected by the negatively charged membranes. In addition, it was found that Mg(OH)2 that precipitates on the membrane can further trap arsenic. Importantly, almost all As(III) passing through the membranes is oxidized to As(V) by hydrogen peroxide produced on the cathode, which significantly decreased its overall toxicity and mobility. Although the high pH along the membrane surface led to mineral scaling, this scale could be partially removed by backwashing the membrane. To the best of our knowledge, this is the first report of effective As(III) removal using low-pressure membranes, with As(III) rejection higher than that achieved by NF and RO, and high water permeance.

Hydrothermal carbonization of anaerobic digestate and manure from a dairy farm on energy recovery and the fate of nutrients.

Hydrothermal carbonization (HTC) of raw and anaerobically digested (AD) manure with either water or whey was studied, with the goal of recovering energy and nutrients. Specifically, the impacts of HTC reaction temperature (180-240 °C), solid feedstock, and type of liquid on hydrochar quality and aqueous phase properties were tested. Of the hydrochars produced, the calorific value of whey-based hydrochar was the highest, (19.4 and 16.0 MJ/kg for manure and digestate, respectively). Overall, the net energy gain was higher for HTC of manure with whey (7.4-8.3 MJ/kg dry feedstock) and water (4.4-5.1 MJ/kg) compared to the combined AD-HTC process with whey (4.4-5.3 MJ/kg) and water (2.3-2.9 MJ/kg). Digestate-derived hydrochar contained up to 1.8% P, higher than manure-derived hydrochar (≤1.5%). Using whey as a liquid for HTC increased the aqueous-phase N-P-K concentrations up to 3,200, 410, and 7,900 mg/L, respectively, suggesting its potential use as a liquid fertilizer.

Linker-Free Magnetite-Decorated Gold Nanoparticles (Fe3O4-Au): Synthesis, Characterization, and Application for Electrochemical Detection of Arsenic (III).

Linker-free magnetite nanoparticles (Fe3O4NPs)-decorated gold nanoparticles (AuNPs) were grown using a new protocol that can be used as a new platform for synthesis of other intact metal-metal oxide nanocomposites without the need for linkers. This minimizes the distance between the metal and metal oxide nanoparticles and ensures the optimum combined effects between the two material interfaces. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy confirmed the successful synthesis of the Fe3O4-Au nanocomposite, without any change in the magnetite phase. Characterization, using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy, revealed the composite to consist of AuNPs of 70 ± 10 nm diameter decorated with tiny 10 ± 3 nm diameter Fe3O4NPs in Au:Fe mass ratio of 5:1. The prepared Fe3O4-Au nanocomposite was embedded in ionic liquid (IL) and applied for the modification of glassy carbon electrode (GCE) for the electrochemical detection of As(III) in water. By combining the excellent catalytic properties of the AuNPs with the high adsorption capacity of the tiny Fe3O4NPs towards As(III), as well as the good conductivity of IL, the Fe3O4-Au-IL nanocomposite showed excellent performance in the square wave anodic stripping voltammetry detection of As(III). Under the optimized conditions, a linear range of 1 to 100 µg/L was achieved with a detection limit of 0.22 µg/L (S/N = 3), and no interference from 100-fold higher concentrations of a wide variety of cations and anions found in water. A very low residual standard deviation of 1.16% confirmed the high precision/reproducibility of As(III) analysis and the reliability of the Fe3O4-Au-IL sensing interface. Finally, this proposed sensing interface was successfully applied to analyzing synthetic river and wastewater samples with a 95-101% recovery, demonstrating excellent accuracy, even in complex synthetic river and wastewater samples containing high concentrations of humic acid without any sample pretreatments.

The evolution of metal size and partitioning throughout the wastewater treatment train.

Understanding the behavior of heavy metals in wastewater is critical for the development of metal removal and detection techniques. In this study, we characterize the dynamic and evolving size and partitioning behavior of lead (Pb), cadmium (Cd), and arsenite (As(III)) throughout the wastewater treatment train (WWTT). Metal concentrations were determined in three size fractions (>0.45 µm, 0.45 µm - 5 kDa, and <5 kDa), and the partitioning/complexation of the metals was quantified for the <0.45 µm fraction. Cd was found to be highly mobile, with the fraction of dissolved Cd gradually increasing throughout the WWTT. As(III) was also highly mobile, with its size distribution and partitioning remaining largely steady, except when FeCl3 was used as a flocculation agent, which led to the formation of arsenic/iron complexes. However, Pb was found primarily in complex forms or adsorbed onto inorganic particulates. The WWTT had little impact on the size and partitioning of Pb, except that the formation of the Pb/iron complex occurred after flocculation with FeCl3. An increase of water hardness slightly increased the metals in the dissolved fraction. Overall, this study provides insight into the evolution of metals throughout the WWTT, offering guidance to users and researchers regarding their treatment and detection.

Bismuth Subcarbonate Decorated Reduced Graphene Oxide Nanocomposite for the Sensitive Stripping Voltammetry Analysis of Pb(II) and Cd(II) in Water.

In this paper, bismuth subcarbonate (BiO)2CO3-reduced graphene oxide nanocomposite incorporated in Nafion matrix ((BiO)2CO3-rGO-Nafion) was synthesized and further applied, for the first time, in the sensitive detection of Pb(II) and Cd(II) by square-wave anodic stripping voltammetry (SWASV). The as-synthesized nanocomposites were characterized by energy-dispersive spectroscopy (EDS), Raman spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). (BiO)2CO3 composite plays a key role in the improvement of the detection sensitivity, which can form multicomponent alloy with cadmium and lead. Additionally, the unique structure of rGO can enlarge the surface area and provide abundant active sites. Moreover, Nafion incorporation in the nanocomposite can effectively increase the adhesion and mechanical strength of the film, and further improve the preconcetration ability due to the cation-exchange capacity of its abundant sulfonate groups. As expected, the (BiO)2CO3-rGO/Nafion nanocomposite-modified glassy carbon electrode ((BiO)2CO3-rGO-Nafion/GCE) achieved low detection limits of 0.24 µg/L for Pb(II) and 0.16 µg/L for Cd(II), in the linear range of 1.0-60 µg/L, and showed some excellent performance, such as high stability, good selectivity, and sensitivity. Finally, synthetic water samples were prepared and further used to verify the practicability of the (BiO)2CO3-rGO-Nafion/GCE with satisfactory results.

Structural Dependence of Reductive Defluorination of Linear PFAS Compounds in a UV/Electrochemical System.

Per and polyfluoroalkyl substances (PFAS), legacy chemicals used in firefighting and the manufacturing of many industrial and consumer goods, are widely found in groundwater resources, along with other regulated compounds, such as chlorinated solvents. Due to their strong C-F bonds, these molecules are extremely recalcitrant, requiring advanced treatment methods for effective remediation, with hydrated electrons shown to be able to defluorinated these compounds. A combined photo/electrochemical method has been demonstrated to dramatically increase defluorination rates, where PFAS molecules sorbed onto appropriately functionalized cathodes charged to low cell potentials (-0.58 V vs Ag/AgCl) undergo a transient electron transfer event from the electrode, which "primes" the molecule by reducing the C-F bond strength and enables the bond's dissociation upon the absorption of a hydrated electron. In this work, we explore the impact of headgroup and chain length on the performance of this two-electron process and extend this technique to chlorinated solvents. We use isotopically labeled PFAS molecules to take advantage of the kinetic isotope effect and demonstrate that indeed PFAS defluorination is likely driven by a two-electron process. We also present density functional theory calculations to illustrate that the externally applied potential resulted in an increased rate of electron transfer, which ultimately increased the measured defluorination rate.

Comparison of the colloidal stability, mobility, and performance of nanoscale zerovalent iron and sulfidated derivatives.

Nanoscale zerovalent iron (nZVI) and sulfidated nanoscale zerovalent iron (S-nZVI) have been increasingly studied for heavy metal removal in the subsurface. However, a comprehensive comparison of the effectiveness of the technologies and the stability of derived metal-adsorbed composites is lacking. In this study, we evaluated the colloidal stability and transport of nZVI, S-nZVI and S-nZVI modified with nanosized silica (FeSSi). Furthermore, we monitored the metal immobilization performance of the three nanoparticles (NPs) under anoxic conditions in synthetic groundwater for 30 days. The NP-metal composites were thereafter discharged into a river water and metal remobilization was monitored for 20 days. Sulfidation improved the colloidal stability of nZVI in both simple media and in natural waters, although a lower initial agglomeration rate constant (ka) was observed in unmodified nZVI at acidic pH. The transport of nZVI in saturated soil column was enhanced with sulfidation due to decreased electrostatic attraction between the NPs and sand. The three NPs sequestered more than 80 % of Cu2+, Zn2+, Cd2+ and Cr2O72- from groundwater. Among the three NPs tested, S-nZVI had a slightly higher removal capacity for metals than nZVI in synthetic groundwater and the chemical stability of metal-S-nZVI composites upon discharge into river water was the highest.

Single and binary protein electroultrafiltration using poly(vinyl-alcohol)-carbon nanotube (PVA-CNT) composite membranes.

Electrically conductive composite ultrafiltration membranes composed of carbon nanotubes have exhibited efficient fouling inhibition in wastewater treatment applications. In the current study, poly(vinyl-alcohol)-carbon nanotube membranes were applied to fed batch crossflow electroultrafiltration of dilute (0.1 g/L of each species) single and binary protein solutions of α-lactalbumin and hen egg-white lysozyme at pH 7.4, 4 mM ionic strength, and 1 psi. Electroultrafiltration using the poly(vinyl-alcohol)-carbon nanotube composite membranes yielded temporary enhancements in sieving for single protein filtration and in selectivity for binary protein separation compared to ultrafiltration using the unmodified PS-35 membranes. Assessment of membrane fouling based on permeate flux, zeta potential measurements, and scanning electron microscopy visualization of the conditioned membranes indicated significant resulting protein adsorption and aggregation which limited the duration of improvement during electroultrafiltration with an applied cathodic potential of -4.6 V (vs. Ag/AgCl). These results imply that appropriate optimization of electroultrafiltration using carbon nanotube-deposited polymeric membranes may provide substantial short-term improvements in binary protein separations.