Electromagnetic Induction of Zerovalent Iron (ZVI) Powder and Nanoscale Zerovalent Iron (NZVI) Particles Enhances Dechlorination of Trichloroethylene in Contaminated Groundwater and Soil: Proof of Concept

This study evaluates the concept of using zerovalent iron (ZVI) powder or nanoscale zerovalent iron (NZVI) particles in combination with a low frequency (150 kHz) AC electromagnetic field (AC EMF) to effectively remove trichloroethylene (TCE) from groundwater and saturated soils. ZVI and NZVI are ferromagnetic, which can induce heat under applied AC EMF. The heat generated by ZVI and NZVI induction can increase the rate of dechlorination, according to Arrhenius’ equation, and increase the rate of TCE desorption from TCE-sorbed soil. Both dechlorination and TCE desorption enhance the overall TCE removal rate. We evaluated this novel concept in laboratory batch reactors. We found that both ZVI and NZVI can induce heat under applied AC EMF up to 120 °C in 20 min. Using ZVI and NZVI with AC EMF enhanced dechlorination of dissolved TCE (no soil) up to 4.96-fold. In addition to increasing the temperature by ZVI and NZVI induction heating, AC EMF increased intrinsic ZVI and NZVI reactivity, ostensibly due to accelerated corrosion, as demonstrated by the increased ORP. In a soil-water-TCE system, NZVI together with AC EMF thermally enhanced desorption of TCE from soil and increased the degradation of TCE up to 5.36-fold compared to the absence of AC EMF. For the first time, this study indicates the potential for ZVI and NZVI coupled with AC EMF as a combined remediation technique for increasing the rate and completeness of in situ cleanup of adsorbed phase contaminants

Partitioning Behavior of Organic Contaminants in Carbon Storage Environments: A Critical Review

Carbon capture and storage is a promising strategy for mitigating the CO₂ contribution to global climate change. The large scale implementation of the technology mandates better understanding of the risks associated with CO₂ injection into geologic formations and the subsequent interactions with groundwater resources. The injected supercritical CO₂ (sc-CO₂) is a nonpolar solvent that can potentially mobilize organic compounds that exist at residual saturation in the formation. Here, we review the partitioning behavior of selected organic compounds typically found in depleted oil reservoirs in the residual oil–brine–sc-CO₂ system under carbon storage conditions. The solubility of pure phase organic compounds in sc-CO₂ and partitioning of organic compounds between water and sc-CO₂ follow trends predicted based on thermodynamics. Compounds with high volatility and low aqueous solubility have the highest potential to partition to sc-CO₂. The partitioning of low volatility compounds to sc-CO₂ can be enhanced by cosolvency due to the presence of higher volatility compounds in the sc-CO₂. The effect of temperature, pressure, salinity, pH, and dissolution of water molecules into sc-CO₂ on the partitioning behavior of organic compounds in the residual oil–brine–sc-CO₂ system is discussed. Data gaps and research needs for models to predict the partitioning of organic compounds in brines and from complex mixtures of oils are presented. Models need to be able to better incorporate the effect of salinity and cosolvency, which will require more experimental data from key classes of organic compounds

Effect of Initial Speciation of Copper- and Silver-Based Nanoparticles on Their Long-Term Fate and Phytoavailability in Freshwater Wetland Mesocosms

Ag⁰- and CuO-engineered nanomaterials (ENMs) or their sulfidized forms are introduced into freshwater wetlands through wastewater effluent and agricultural runoff. Knowledge about the rates of transformations of these ENMs in realistic environments and the impact of the form of the incoming ENM (i.e., sulfidized or pristine) on bioavailability and fate is limited. Here, five freshwater wetland mesocosms were exposed to 3 g of total metal as CuO, CuS, Ag⁰, or Ag₂S ENMs or soluble CuNO₃ added weekly for 1 month. Total metal and metal speciation was measured in sediment and plant samples collected 1, 3, 6, and 9 months after addition. The form of the added ENM did not affect the metal distribution, and ENMs distributed similarly to added ionic Cu or Ag. For the dosing condition used, ∼50% of the added Ag or Cu metal mass was found in <i>Egeria densa</i> plant tissue, with the remainder primarily in the surficial sediment. Ag⁰ and CuO ENMs transformed quickly in sediment, with no evidence of CuO and only ∼4% of silver present as Ag⁰ ENM 1 week after the last ENM addition. In contrast to sediment, Ag⁰ and CuO ENMs were persistent in <i>E. densa</i> tissues for up to 9 and 6 months, respectively. The persistence of ENMs in <i>E. densa</i> suggests that chronic exposures, or food web transfers, for both the transformed and the initially added ENMs are possible

Measurement and Modeling of Setschenow Constants for Selected Hydrophilic Compounds in NaCl and CaCl₂ Simulated Carbon Storage Brines

ConspectusCarbon capture, utilization, and storage (CCUS), a climate change mitigation strategy, along with unconventional oil and gas extraction, generates enormous volumes of produced water containing high salt concentrations and a litany of organic compounds. Understanding the aqueous solubility of organic compounds related to these operations is important for water treatment and reuse alternatives, as well as risk assessment purposes. The well-established Setschenow equation can be used to determine the effect of salts on aqueous solubility. However, there is a lack of reported Setschenow constants, especially for polar organic compounds.In this study, the Setschenow constants for selected hydrophilic organic compounds were experimentally determined, and linear free energy models for predicting the Setschenow constant of organic chemicals in concentrated brines were developed. Solid phase microextraction was employed to measure the salting-out behavior of six selected hydrophilic compounds up to 5 M NaCl and 2 M CaCl₂ and in Na–Ca–Cl brines. All compounds, which include phenol, <i>p</i>-cresol, hydroquinone, pyrrole, hexanoic acid, and 9-hydroxyfluorene, exhibited log–linear behavior up to these concentrations, meaning Setschenow constants previously measured at low salt concentrations can be extrapolated up to high salt concentrations for hydrophilic compounds. Setschenow constants measured in NaCl and CaCl₂ brines are additive for the compounds measured here; meaning Setschenow constants measured in single salt solutions can be used in multiple salt solutions.The hydrophilic compounds in this study were selected to elucidate differences in salting-out behavior based on their chemical structure. Using data from this study, as well as literature data, linear free energy relationships (LFERs) for prediction of NaCl, CaCl₂, LiCl, and NaBr Setschenow constants were developed and validated. Two LFERs were improved. One LFER uses the Abraham solvation parameters, which include the index of refraction of the organic compound, organic compound’s polarizability, hydrogen bonding acidity and basicity of the organic compound, and the molar volume of the compound. The other uses an octanol–water partitioning coefficient to predict NaCl Setschenow constants. Improved models from this study now include organic compounds that are structurally and chemically more diverse than the previous models. The CaCl₂, LiCl, and NaBr single parameter LFERs use concepts from the Hofmeister series to predict new, respective Setschenow constants from NaCl Setschenow constants. The Setschenow constants determined here, as well as the LFERs developed, can be incorporated into CCUS reactive transport models to predict aqueous solubility and partitioning coefficients of organic compounds. This work also has implications for beneficial reuse of water from CCUS; this can aide in determining treatment technologies for produced waters

Natural Organic Matter Alters Biofilm Tolerance to Silver Nanoparticles and Dissolved Silver

Motivated by the need to understand environmental risks posed by potentially biocidal engineered nanoparticles, the effects of silver nanoparticle (AgNP) exposure on viability in single species Pseudomonas fluorescens biofilms were determined via dye staining methods. AgNP dispersions, containing both particles and dissolved silver originating from the particles, negatively impacted biofilm viability in a dose-dependent manner. No silver treatments (up to 100 ppm AgNPs) resulted in 100% biofilm viability loss, even though these same concentrations caused complete viability loss in planktonic culture, suggesting some biofilm tolerance to AgNP toxicity. Colloidally stable AgNP suspensions exhibited greater toxicity to biofilms than corresponding particle-free supernatants containing only dissolved silver released from the particles. This distinct nanoparticle-specific toxicity was not observed for less stable, highly aggregated particles, suggesting that biofilms were protected against nanoparticle aggregate toxicity. In both the stable and highly aggregated dispersions, dissolved silver made a significant contribution to overall toxicity. Therefore, despite increased colloidal stability when humic acid adsorbed to AgNPs, the presence of humic acid mitigated the toxicity of AgNP suspensions because it bound to silver ions in solution

Effect of Applied Voltage, Initial Concentration, and Natural Organic Matter on Sequential Reduction/Oxidation of Nitrobenzene by Graphite Electrodes

Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H₂ at the cathode and oxidizing conditions and O₂ at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration, and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (<i>k</i>_NB) and NSB (<i>k</i>_NSB) increased with applied voltage between 2 V and 3.5 V (when the initial NB concentration was 100 μM, <i>k</i>_NB = 0.3 h^–1 and <i>k</i>_NSB = 0.04 h^–1at 2 V; k_NB = 1.6 h^–1 and k_NSB = 0.64 h^–1at 3.5 V) but stopped increasing beyond the threshold of 3.5 V. When initial NB concentration decreased from 100 to 5 μM, <i>k</i>_NB and <i>k</i>_NSB became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased <i>k</i>_NB while slightly increased <i>k</i>_NSB, but only to a limited extent (∼factor of 3) for dissolved organic carbon content up to 100 mg/L. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation

Effects of Molecular Weight Distribution and Chemical Properties of Natural Organic Matter on Gold Nanoparticle Aggregation

The complexity of natural organic matter (NOM) motivates determination of how specific components in a NOM mixture interact with and affect nanoparticle (NP) behavior. The effects of two Suwannee River NOM fractions (separated by a 100,000 g/mol ultrafiltration membrane) on gold NP aggregation are compared. The weight-average molecular weight, <i>M</i>_<i>w</i>, for the unfractionated NOM was 23,300 g/mol, determined by size exclusion chromatography with multiangle light scattering. The NOM was comprised of ∼1.8 wt % of >100,000 g/mol retentate (NOM_r, <i>M</i>_<i>w</i> = 691,000 g/mol) and 98 wt % of filtrate (NOM_f, <i>M</i>_<i>w</i> = 12,800 g/mol). Ten ppm of NOM_r provided significantly better NP stability against aggregation than 10 ppm of NOM_f in 100 mM NaCl due to steric effects. In the unfractionated NOM, the relative importance of the two components was concentration-dependent. For a low concentration of unfractionated NOM (10 ppm), both fractions contributed to the NOM effects; for a high concentration (560 ppm), NP stability was controlled by the small amount (10 ppm) of NOM_r present, rather than the higher amount (550 ppm) of NOM_f. Therefore, large humic aggregates in a heterogeneous NOM sample can have disproportionately strong effects, and characterization of <i>M</i>_<i>w</i> distributions (rather than average <i>M</i>_<i>w</i>) may be required to explain NOM effects on NP behavior

Sulfidation Mechanism for Zinc Oxide Nanoparticles and the Effect of Sulfidation on Their Solubility

Environmental transformations of nanoparticles (NPs) affect their properties and toxicity potential. Sulfidation is an important transformation process affecting the fate of NPs containing metal cations with an affinity for sulfide. Here, the extent and mechanism of sulfidation of ZnO NPs were investigated, and the properties of resulting products were carefully characterized. Synchrotron X-ray absorption spectroscopy and X-ray diffraction analysis reveal that transformation of ZnO to ZnS occurs readily at ambient temperature in the presence of inorganic sulfide. The extent of sulfidation depends on sulfide concentration, and close to 100% conversion can be obtained in 5 days given sufficient addition of sulfide. X-ray diffraction and transmission electron microscopy showed formation of primarily ZnS NPs smaller than 5 nm, indicating that sulfidation of ZnO NPs occurs by a dissolution and reprecipitation mechanism. The solubility of partially sulfidized ZnO NPs is controlled by the remaining ZnO core and not quenched by a ZnS shell formed as was observed for partially sulfidized Ag NPs. Sulfidation also led to NP aggregation and a decrease of surface charge. These changes suggest that sulfidation of ZnO NPs alters the behavior, fate, and toxicity of ZnO NPs in the environment. The reactivity and fate of the resulting <5 nm ZnS particles remains to be determined

Bacterial Nanocellulose Aerogel Membranes: Novel High-Porosity Materials for Membrane Distillation

We fabricated, characterized, and tested novel fibrous aerogel membranes in direct contact membrane distillation (MD) to elucidate the effects of a model high-porosity membrane material on MD performance. Unsupported bacterial nanocellulose aerogels exhibit higher porosity, thinner fibers, and lower bulk thermal conductivity than any previously reported MD materials. Modeling and experiments demonstrate that these material properties confer significantly higher intrinsic membrane permeability and thermal efficiency than symmetric PVDF phase inversion membranes with lower porosity. Development of macroporous fibrous membranes with aerogel-like porosity and thermal conductivity (>98% and <0.03 W m^–1 K^–1, respectively) in thinner-film formats may further improve MD flux

Time and Nanoparticle Concentration Affect the Extractability of Cu from CuO NP-Amended Soil

We assess the effect of CuO nanoparticle (NP) concentration and soil aging time on the extractability of Cu from a standard sandy soil (Lufa 2.1). The soil was dosed with CuO NPs or Cu­(NO3)­2 at 10 mg/kg or 100 mg/kg of total added Cu, and then extracted using either 0.01 M CaCl₂ or 0.005 M diethylenetriaminepentaacetic acid (DTPA) (pH 7.6) extraction fluid at selected times over 31 days. For the high dose of CuO NPs, the amount of DTPA-extractable Cu in soil increased from 3 wt % immediately after mixing to 38 wt % after 31 days. In contrast, the extractability of Cu­(NO₃)₂ was highest initially, decreasing with time. The increase in extractability was attributed to dissolution of CuO NPs in the soil. This was confirmed with synchrotron X-ray absorption near edge structure measurements. The CuO NP dissolution kinetics were modeled by a first-order dissolution model. Our findings indicate that dissolution, concentration, and aging time are important factors that influence Cu extractability in CuO NP-amended soil and suggest that a time-dependent series of extractions could be developed as a functional assay to determine the dissolution rate constant