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The salt removal capacity (SRC) of the carbon electrodes in membrane capacitive deionization (MCDI) is limited by the applied potential (

Neutralization of the bio-oil pH has been shown to generate a neutralized bio-oil aqueous phase (NBOAP) that includes most of the acidic components and a neutralized bio-oil organic phase (NBOOP) that includes hydrophobic organics, such as phenols. NBOOP can be used for fuel production, while NBOAP can be fed to microbial electrolysis cells (MECs) for hydrogen production. After pH neutralization, some organic acidic components remain in NBOOP. This work is focused on capturing acidic compounds from NBOOP through water extraction and electrosorption, and demonstrating hydrogen production via MECs. Capacitive deionization (CDI) is proven effective in capturing ions from NBOOP-contacted water and NBOAP via electrosorption. Captured acidic compounds enable the MEC application to effectively produce renewable hydrogen. Chemical oxygen demand (COD) removal of 49.2%, 61.5%, and 60.8% for 2, 4, and 10 g/L-anode/day loading were observed, corresponding to a total COD degradation of 0.19 g/L, 0.79 g/L, and 1.3 g/L, respectively. A maximum hydrogen productivity of 4.3 L-H2/L-anode/day was obtained. Major compounds in the water phase such as fatty acids, sugar derivatives, furanic and phenolic compounds were converted to hydrogen with an efficiency of 80–90%. This approach may lead the entire biomass pyrolysis process to be an overall carbon-neutral process.

This study focuses on the influence of hydrophilic groups and metal-ion loading on adsorbent polymer conformation, which controls access to adsorption sites and may limit adsorption capacity. Gaining a better understanding of the factors that influence conformation may yield higher-capacity adsorbents. Polyamidoxime (PAO), deuterated-PAO polyacrylic acid diblock copolymers (d-PAO-b-PAA), and randomly configured copolymers (PAO-co-PAA) were synthesized and characterized by neutron reflectometry in air and D2O. For d-PAO-b-PAA, characterization was also performed after alkali conditioning and in simulated seawater. PAO and PAO-co-PAA, with similar molecular weight and grafting density, extended from 95-A thickness in air to 180 and 280-A in D2O, respectively. This result suggests that polymer swelling may cause the additional adsorption capacity observed when polymer hydrophilicity increases. Two d-PAO-b-PAA samples, A and B, with a d-PAO thickness of 55-A swelled to 110-A and 140-A, respectively, with an overall thickness increase of ∼160% in D2O. After alkali conditioning, molecular interactions increased the density of PAA near the PAO-PAA interface, while the d-PAO thickness only decreased by ∼10 A. The d-PAO thickness of both samples declined to ∼90-A after adsorption in simulated seawater due to polymer-chain crosslinking. These results are expected to aid in improving adsorbent synthesis to increase uranium capacity.

Compositional changes by the decay of radionuclides in radioactive aerosols can influence their charging state, coagulation frequency and size distribution throughout their atmospheric lifetime. The importance of such effects is unknown as they have not been considered in microphysical and global radioactivity transport studies to date. We explore the effects of compositional changes on the charging efficiency and coagulation rates of aerosols using a set of kinetic equations that couple all relevant processes (decay, charging and coagulation) and their evolution over time. Compared to a coupled aggregation-tracer model for the prediction of the radioactive composition of particulates undergoing coagulation, our kinetic approach can provide similar results using much less central processing unit time. Together with other considerations, our approach is computational efficient enough to allow implementation in 3D atmospheric transport models. The decay of radionuclides and the production of decay products within radioactive aerosols may significantly affect the aerosol charging rates, and either hinder or promote the coagulation of multicomponent radioactive aerosols. These results suggest that radiological phenomena occurring within radioactive aerosols, as well as subsequent effects on aerosol microphysics, should be considered in regional and global models to more accurately predict radioactivity transport in the atmosphere in case of a nuclear plant accident.

Bio-oil or pyrolysis oil — a product of thermochemical decomposition of biomass under oxygen-limited conditions — holds great potential to be a substitute for nonrenewable fossil fuels. However, its high acidity, which is primarily due to the degradation of hemicelluloses, limits its applications. For the evaluation of bio-oil production and treatment, it is essential to accurately measure the acidity of bio-oil. The total acid number (TAN), which is defined as the amount of potassium hydroxide needed to titrate one gram of a sample and has been established as an ASTM method to measure the acidity of petroleum products, has been employed to investigate the acidity of bio-oil. The TAN values of different concentrations of bio-oil components such as standard solutions of acetic acid, propionic acid, vanillic acid, hydroxybenzoic acid, syringic acid, hydroxymethylfurfural, and phenol were analyzed according to the ASTM D664 standard method. This method showed the same linear relationship between the TAN values and the molar concentrations of acetic, propionic, and hydroxybenzoic acids. A different linear relationship was found for vanillic acid, due to the presence of multiple functional groups that can contribute to the TAN value. The influence of the titration solvent on the TAN values has been determined by comparing the TAN values and titration curves obtained from the standard method with results from the TAN analysis in aqueous environment and with equilibrium modeling results. Aqueous bio-oil samples with a known amount of acetic acid added were also analyzed. The additional acetic acid in bio-oil samples caused a proportional increase in the TAN values. The results of this research indicate that the TAN value of a sample with acids acting as monoprotic acids in the titration solvent can be converted to the molar concentration of total acids. For a sample containing acids that act as diprotic and polyprotic acids, however, its TAN value cannot be simply converted to the molar concentration of total acids because these acids have a stronger contribution to the TAN values than the contribution of monoprotic acids.

One of the current barriers to achieving fast and stable performance for flow-electrode capacitive deionization (FCDI) is determining optimal operating parameters. To date, however, no consensus has been reached for universal conditions for FCDI. Through experimental and modeling approaches in this study, we systematically evaluated the influence of applied potential (V = 1.2–2.4 V) and electrolyte concentration (C0 = 0.05–0.5 M) on the FCDI and electrodialysis (ED) desalination processes. Evaluation indicators include the concentration decrease in the desalinated solution, salt removal rates, pH fluctuations, charge efficiency, and energy consumption. Results demonstrated that the dynamic curves of concentration decrease at 2.0 V nearly overlapped with the response at 1.6 V at certain electrolyte concentrations, while the salt removal rates at 0.2 M salt concentration were the best among all concentrations tested at a range of applied potential. It was thus concluded that the optimum conditions for FCDI operation are 1.6 V applied potential and 0.2 M initial salt concentration, under which faradaic reactions are not being triggered, and concentration polarization does not significantly affect ion transfer. Furthermore, a comparative study between FCDI and ED indicated that ED has a different dependence on the electrolyte concentration and applied potential, in which the desalination can be linearly enhanced with increasing potential but greatly limited at high concentrations. Due to the presence of carbon particles in FCDI, the enhanced charge/ion transfer is probably the main reason for the different desalination performance of FCDI and ED. The optimal operating parameters obtained in this work could be used as basic test conditions for further development of new carbon-based materials for FCDI.

The influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorption on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.

Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Toth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can be further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set of optimal GSTA parameters, both dimensional and non-dimensional, as well as the corresponding thermodynamic parameters necessary to predict the behavior of the system at temperatures for which data were not available. It will be shown that this code, utilizing the GSTA model, was able to describe a wide variety of gas-solid adsorption systems at equilibrium. Additionally, a physical interpretation of these results will be provided, as well as an alternate derivation of the GSTA model, which intends to reaffirm the physical meaning.

Radioactive decay processes, such as alpha decay, produce decay chains where the mass numbers of nuclides decrease as larger nuclides expel energetic particles to form smaller nuclides. Under these conditions, the coefficient matrix that describes the differential rate expressions for radioactive decay can be made lower triangular. With this special structure, formulating an algebraic solution to the decay chains can be done by first formulating the eigenvectors that make up the coefficient matrix, which can then be solved using forward substitution for a lower triangular matrix. This work details the derivation of algebraic solutions for decay chains of any number of stable and unstable nuclides with any number of branching based on this eigenvector analysis. A prototype computational code was developed to validate and compare this methodology against a number of other methods for solving similar systems. A two-phase sorting algorithm yielding the lower triangular matrix structure was established to apply the developed algebraic solutions for decay chains involving beta-emitting radionuclides transformed into daughter nuclides without change in their mass number. The methodologies produced in this work provide an efficient way to estimate nuclide fractions from natural decay processes.

The influence of low-amplitude, high-frequency, pulsed electrical potential on ion transport in mesoporous carbon electrodes has been investigated. Mesoporous carbon electrodes of approximately 10-nm average pore size were synthesized based on a soft-template method. The carbon electrodes were used in capacitive deionization experiments with salt solutions consisting of a mixture of ions of concentrations ranging from 5000 ppm to 10,000 ppm to investigate the effect of a pulsed potential on the ion removal rate. Higher rates of sorption and regeneration were observed when the pulsed potential was superimposed on a direct current (DC) offset of 1.2 V that is typically applied in capacitive deionization (CDI). The rate of ion sorption in CDI experiments was dependant on the amplitude and frequency of the pulsed potential. Conductivity measurements showed enhancement in transport rates due to the pulsed potential up to 130%. The effect was stronger during regeneration. Neutron imaging, a visualization technique, was also employed to quantify the diffusion of ions through mesoporous carbon electrodes under different conditions. Sequences of neutron images showed enhanced transport of gadolinium ions under the influence of pulsed potential. From the concentration histories of gadolinium ions inside the carbon electrodes, the effective diffusion coefficient of gadolinium ions was estimated at 8.3 ± 0.4 × 10−11 m2/s at 1.2 V DC and 1.1 × 10−10 m2/s at 1.2 V DC with pulsed potential added.

Bacterial spore interactions with planar surfaces in aquatic environments, including adhesive forces and force–distance profiles, are influenced by the geometry and physicochemical properties of the system. The characteristics of spores of Bacillus thuringiensis (Bt) are determined using electron microscopy and electrokinetic measurements. The average size of the spores is 1.57 μm long and 0.86 μm wide, and the zeta potential values are negative for the solutions used in this work. The zeta potentials of the spores and mica surfaces used in the experiments are measured as a function of pH and ionic strength. The Derjaguin, Landau, Verwey and Overbeek (DLVO) theory is employed to predict the interaction force between the spores and planar surfaces as a function of the separation distance, and a force balance is used to explain the adhesive force. Theoretical estimations are compared to experimental measurements obtained from atomic force microscopy (AFM). The DLVO-based calculations are consistent with AFM force measurements, while the calculated adhesive force shows some deviations from the measurements. The deviations can be minimized by considering the roughness of the Bt spore and substrate surfaces. Results are important in the understanding of spore interactions with environmental surfaces in aquatic systems.

Off-gases produced during the reprocessing of used nuclear fuel (UNF) include 129I2, 3HHO, 14CO2, 85Kr, and 135Xe, which are volatilized out into the off-gas. In order to meet regulatory requirements for reprocessing plant emissions, these gases must be captured and removed from the off-gas stream prior to off-gas emission. Of particular interest are the noble gases, Kr and Xe, which can be fairly difficult to remove from the off-gas due to their low chemical reactivity. Thus, this work is focused on utilizing engineered adsorbents, AgZ-PAN and HZ-PAN, to capture Kr and Xe from a mixed-gas stream at relatively low temperatures (191–295 K) and various flow rates (50–2000 mL/min). Isothermal data for Kr and Xe on each adsorbent are analyzed to produce the Langmuir parameters needed to model the mixture adsorption capacities at relevant temperatures using the Extended Langmuir model. Those parameters are then incorporated into a fixed-bed adsorption model developed in this work using the Mulitphysics Object-Oriented Simulation Environment (MOOSE). That model is used to simulate breakthrough times for Kr and Xe in packed columns of AgZ-PAN and HZ-PAN, ranging in length from 6 to 20 in., at relevant temperatures and flow rates. Breakthrough times varied from nearly instantaneous for Kr in AgZ-PAN to 30 h for Xe in HZ-PAN. After the developed model was validated by comparisons with experimental breakthrough data, the model framework was used to simulate the performance of multiple fixed-bed columns connected in series.

Based on the electrosorption of ions by charged electrodes, the capacitive deionization method was considered for ion removal from saline water using mesoporous carbon electrodes. Mesoporous carbon was synthesized via a self-assembly method, with a narrow pore size distribution in the range of 6–10 nm. It was found that the rates of ion sorption and release by mesoporous carbon electrodes increase with an increase in the temperature of the solution. A drift in the conductivity was observed during electrosorption of Instant Ocean solutions, which may be explained as the result of competition between ions of different valence and size. The diffusion coefficient of ions during electrosorption was evaluated as a function of temperature, and a transport model coupled with an electrical-double-layer model was employed to calculate the mass of salt adsorbed by the electrodes. The calculated cumulative mass of salt captured in the electrical double layers of the electrodes was compared to the experimental data at different temperatures.

Enzyme fuel cells (EFCs) offer some advantages over traditional precious-metal-catalyzed fuel cells, such as polymer electrolyte membrane fuel cells (PEMFCs). However, EFCs exhibit far less power output than PEMFCs and have relatively short life spans before materials must be replaced. In this work, electrochemical impedance spectroscopy (EIS) is used to analyze the internal resistances throughout the EFC at a variety of operating conditions. EIS analysis is focused primarily on the resistances of the anode, solution/membrane, and cathode. Increased enzyme loading results in improved power output and reductions in internal resistance. Conditions are identified for which enzyme loading does not limit the EFC performance. EIS experiments are also reported for EFCs operated continuously for 2 days; power output declines sharply over time, while all internal resistances increase. Drying of the cathode and enzyme/mediator degradation are believed to have contributed to this behavior. Finally, experiments are performed at varying air-humidification temperatures. Little effect on internal resistances or power output is observed. However, it is anticipated that increased air humidification can improve longevity by delivering more water to the cathode. Improvements to the enzymatic cathode are needed for EFC development. These improvements need to focus on improving transport rather than increasing enzyme loading.

Neutron imaging was used to study cathode water content over time in a three-dimensional-cathode enzyme fuel cell (EFC). A porous carbon felt cathode allowed air to flow through the electrode. A solution with laccase and a mediator formed an aqueous layer on the electrode surface. Water loss was observed in situ via neutron imaging for varying experimental conditions, including flow rates of hydrogen and air, cathode inlet humidity, volume of enzyme solution, and its composition. Cathode water loss occurred for all experimental conditions, but the loss rate was noticeably reduced when a high-salt-concentration enzyme solution was used in the cathode in conjunction with increased humidity in the air feed stream. Results from neutron imaging and power density analysis were used in analyzing the causes that could contribute to EFC water loss. An increase in temperature due to the exothermic cathode reaction is considered a plausible cause of cathode water loss via evaporation. This is the first reported application of neutron imaging as a technique to study EFC water management. The results suggest that neutron imaging can be employed to provide a better understanding of EFC phenomena and thereby contribute to design and operational improvements of EFCs.

Although some differences have been observed, the transport behavior of radioactive aerosol particles has often been assumed to be analogous to the behavior of nonradioactive aerosols in dispersion models. However, radioactive particles can become electrostatically charged as a result of the decay process. Theories have been proposed to describe this self-charging phenomenon, which may have a significant effect on how these particles interact with one another and with charged surfaces in the environment. In this study, atomic force microscopy (AFM) was employed to quantify surface forces between a particle and a planar surface and to compare measurements with and without the involvement of radioactivity. The main objective of this work is to assess directly the effects of radioactivity on the surface interactions of radioactive aerosols via the measurement of the adhesion force. The adhesion force between a silicon nitride AFM tip and an activated gold substrate was measured so that any possible effects due to radioactivity could be observed. The adhesion force between the tip and the gold surface increased significantly when the gold substrate (25 mm{sup 2} surface area) was activated to a level of approximately 0.6 mCi. The results of this investigation will prompt further work into themore » effects of radioactivity in particle-surface interactions.« less

The fundamental mechanism of electrosorption of ions developing a double layer inside nanopores was studied via a combination of experimental and theoretical studies. A novel graphitized-carbon monolithic material has proven to be a good electrical double-layer capacitor that can be applied in the separation of ions from aqueous solutions. An extended electrical double-layer model indicated that the pore size distribution plays a key role in determining the double-layer capacitance in an electrosorption process. Because of the occurrence of double-layer overlapping in narrow pores, mesopores and micropores make significantly different contributions to the double-layer capacitance. Mesopores show good electrochemical accessibility. Micropores present a slow mass transfer of ions and a considerable loss of double-layer capacitance, associated with a shallow potential distribution inside pores. The formation of the diffuse layer inside the micropores determines the magnitude of the double-layer capacitance at low electrolyte concentrations and at conditions close to the point of zero charge of the material. The effect of the double-layer overlapping on the electrosorption capacitance can be reduced by increasing the pore size, electrolyte concentration, and applied potential. The results are relevant to water deionization.

This study investigates the effect of surfactants and key design parameters on the removal efficiency (RE) of paramagnetic colloidal particles by high-gradient magnetic filtration, and attempts to predict the effect of these parameters by a trajectory model. Magnetic filtration offers an advantage over conventional filtration in that it can achieve a reversible and selective separation. An aqueous suspension of paramagnetic colloidal ferric oxide (Fe 2 O 3 ) particles was treated with sodium dodecyl sulfate (SDS) and delivered through a column containing a stainless steel wool filter matrix, which was mounted between the poles of an electromagnet. The RE of the surfactant-treated particles was measured by analyzing effluent samples for Fe 2 O 3 concentration. The effect of the applied magnetic induction, fluid velocity, and radius of the stainless steel wires on the RE was tested and compared for both surfactant-treated and untreated particles. These three factors had a marked effect on the RE of surfactant-treated particles. An increase in applied magnetic induction from 0.2 to 0.5 T increased the RE from 79.9 to 93.4%, a decrease in wire radius from 49 to 15 μm increased the RE from 60.2 to 93.4%, and a decrease in fluid velocity from 0.5 to 0.1 cm/s increased the RE from 69.5 to 95.3%. In the absence of a magnetic field (0 T), the RE was 10.8%. The predictions of the trajectory model agreed closely with these results. The same factors had a negligible effect on the RE of untreated particles. Over the range of all three parameters, the RE varied from 90 to 99%, but these variations were not statistically significant. In the absence of applied magnetic induction, the RE was 90.1%. These results differed markedly from the trajectory model predictions and demonstrated that nonmagnetic filtration mechanisms are primarily responsible for the capture of particles without SDS. Regeneration experiments indicated that the particles were captured in the primary minimum of the potential energy. On the other hand, these results showed that the magnetic filtration mechanism is primarily responsible for the removal of particles treated with SDS and that these particles are captured in the secondary minimum of the potential energy. Therefore, surfactant adsorption onto colloidal particles can potentially preserve and enhance the advantages of magnetic filtration (e.g., reversibility and selectivity).

The study of aggregation of colloidal particles involves assessment of the thermodynamics and kinetics of the process and the characteristics of the phase formed. In this article, recent contributions to the understanding of aggregation are discussed from two different perspectives: (1) developments following the classical treatment and (2) new molecular approaches.

Recent advances in the application of electric fields to interface modification, leading to drop breakup and coalescence in liquid–liquid dispersions or particle aggregation in solid–liquid suspensions, are reviewed in this article. Potential new applications based on electrospray and electrocoalescence of droplets are discussed. Both of these phenomena may occur under applied electric fields and may apply to drops, particles or bubbles. Several industrial applications take advantage of electric fields. Some of these applications are based on well-understood phenomena, such as normal electrospray of droplets (e.g., as in ink jet printing), while others are less understood (e.g., inverse electrospray). Recent developments of electric-field effects and applications, as well as expected future directions, are discussed.

A sorption modeling approach based on surface complexation concepts was applied to predict copper uptake and its effects on the surface electrostatic potential of ferric oxide and silica colloids. Equilibrium modeling of copper uptake by ferric oxide using the traditional surface complexation model (SCM) was reasonably successful with some discrepancies especially in the acidic pH ranges and high colloid concentration cases. Good predictions of the ferric oxide charge reversals during uptake were obtained from the modeling. Based on the SCM predictions, copper removal from solution is due to the outer-sphere complexation of the first hydrolysis product, resulting in the surface-metal complex SO − CuOH + . The SCM was found to be insufficient to describe copper uptake by silica particles. To address discrepancies between experimental data and SCM predictions, the SCM was modified to include attributes of the surface polymer model (SPM), which incorporates sorption of the dimeric copper species Cu 2 (OH) 2 2+ . The continuum model (CM) was also studied as a second modification to the SCM to include formation of surface precipitates. Both the SPM and the CM were successful in modeling copper uptake and ζ potential variations as a function of pH at various solution conditions and colloid concentrations. From the SPM and CM predictions, it was concluded that for systems with high surface loadings, copper removal from solution occurs due to the formation of both monomeric and dimeric surface complexes, as well as through precipitation mechanisms.

Cyclic voltammetry experiments at various electrolyte solution concentrations (0.001–0.1 M) and scan rates (1 to 5 mV s −1 ) have been performed to study the electrical double layer (edl) formation in nanostructured carbon aerogel. The results show that carbon aerogel is a good edl capacitor and can be further divided into mesoporous and microporous capacitors. According to the experiments, the mesoporous capacitor shows a fast charging/discharging response and is only minimally affected by the electrolyte concentration and scan rate. Therefore, the specific capacitance of the mesoporous capacitor is found to be constant over a wide range of applied electrical potentials. On the other hand, the microporous capacitor shows a slow charging/discharging response and its capacitance strongly depends on the electrolyte concentration and potential. Unlike previous experiments, in which only a flat minimum was observed at the point of zero charge (pzc), in the current study, a deep minimum is observed near the pzc at low electrolyte concentration if a slow scan rate is used. This unique feature is a result of edl overlapping in the micropores and is consistent with the predictions by the Gouy–Chapman model employed in this study. Based on this behavior, a new approach is suggested for pzc measurements of solid porous materials for which a large portion of the surface area is in the micropore region.

Experimental studies were carried out to determine the effects of influent pH, ionic strength, metal concentration, and empty-bed contact time (EBCT) on copper sorption in the activated carbon fixed-bed columns. As the influent pH was increased, the column performance significantly improved. An overshoot of the effluent concentration was observed at pH 3.0 due to desorption of copper from the surface–metal complexes. The uptake enhanced as the ionic strength was increased; however, this role was much weaker than that of pH. An increase in metal concentration resulted in a decrease in the bed volumes at the breakthrough. In the beginning of all the experiments, the effluent pH increased dramatically and then dropped and approached lower values. Less sorption was observed when prewashed columns were used, in which the pH in the columns was kept constant. Modelling of the metal sorption in the prewashed columns was performed using a metal ion transport model hydrogeochem and a fixed-bed model.

Electrosorption is generally defined as potential-induced adsorption on the surface of charged electrodes. After polarization of the electrodes, ions are removed from the electrolyte solution by the imposed electric field and adsorbed onto the surface of the electrodes. Experimental and modeling studies were conducted using two types of carbon aerogel composites of different surface areas to provide a better understanding on the mechanisms of electrosorption. The experimental results revealed that no significant specific adsorption of F− ions occurred, while strong specific adsorption was observed for NO3− and Cu2+ ions. In addition, although the two types of carbon aerogel electrodes had different surface areas, their capacities were found to be very similar because of the electrical double-layer overlapping effect in micropores. An electrical double-layer model developed in our previous work (16), in which the electrical double-layer overlapping correction is included, is expanded in the present work by considering the effect of the specific adsorption on the electrosorption process. Modeling results were compared with experimental data obtained under various conditions. When the overlapping effect and specific adsorption were considered, the model provided results that were in good agreement with experimental data.

This study investigates the transition from reversible secondary to irreversible primary-minimum aggregation of superparamagnetic particles in surfactant solutions. The magnetic induction at which this transition occurs is experimentally determined by visualization of chain formation under a magnetic field and chain breakup after the field is removed. The value of the theoretical transitional magnetic induction is calculated from the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, which includes van der Waals, electrostatic, and magnetic-dipole forces, as well as non-DLVO steric repulsion. Experimental results show that the transitional magnetic induction increases with higher concentrations of sodium dodecyl sulfate (SDS). When the surfactant concentration is high, the theoretical value of transitional magnetic induction agrees well with the experimental value. Only when the surface of the particles is completely covered by surfactant molecules can the secondary-minimum chains break up quickly to form a uniformly dispersed particle suspension after the magnetic force is removed. Moreover, such investigations reveal that the primary-minimum chains are shorter when they are formed in solutions of higher concentrations of SDS. This phenomenon occurs because the nonequilibrium steric repulsion between adsorbed SDS layers on the surface of the particles allows the transition from secondary- to primary-minimum aggregation for some of the particles in a chain. When the SDS segments are not adequately compressed, long chains formed in SDS solutions break up at points of secondary-minimum aggregation after removal of the magnetic force. At these points, the adsorbed SDS layers keep particles away from the primary-minimum, leading to the breakup of long chains and formation of short primary-minimum magnetic chains.

Copper uptake by ferric oxide and silica particles is studied through batch kinetic experiments. Copper uptake rates are found to be strongly dependent on pH and on the sorbate/sorbent molar concentration ratio. Dramatic changes to the zeta potential of both colloids from baseline values are observed. Modeling of copper uptake and zeta potential charge reversals using the surface complexation model (SCM) yields poor descriptions under high surface coverage conditions. The conventional SCM, modified in the recent literature to (i) the surface polymer model (SPM), which additionally incorporates uptake of dimeric copper species; and (ii) the continuum model (CM), which includes formation of surface precipitates, is extended here to model uptake kinetics. Both the SPM and the CM are successful in modeling copper uptake rates as well as zeta potential variations over a wide range of solution conditions. For systems with high surface loadings, copper removal from solution appears to result from the formation of monomeric and dimeric surface complexes, as well as through precipitation mechanisms. It is further concluded that a kinetic model incorporating diffusion through the surface film of sorbed and precipitated copper species as the rate-limiting process, in association with the SPM and CM, successfully describes the effect of pH and colloid concentration on copper uptake and oxide particle zeta potential histories.

X-ray photoelectron spectroscopy (XPS) is employed to study chemical interactions between three metal ions — Cu(II), Mo(VI), and Cr(VI) — and chitosan, a natural biopolymer extracted from crab shells. Three forms of chitosan are used — flakes, beads, and modified beads obtained by glutaraldehyde cross-linking. XPS provides identification of the sorption sites involved in the accumulation of metals, as well as the forms of species sorbed on the biopolymer. It is found that sorption occurs on amine functional groups for all the three metals. With copper, the sorption step is not followed by reduction of the metal. More complex phenomena are involved in molybdate removal. A partial reduction (about 20–25% of the total molybdenum content) occurs with chitosan beads and flakes. The distribution of reduced Mo(V) on the surface of the sorbent differs from that in the bulk of the sorbent for raw chitosan beads, while the glutaraldehyde cross-linking allows uniform distribution of reduced Mo(V) throughout the sorbent. The difference between these two forms of chitosan can be related to a complementary photoreduction step occurring on the surface of the biopolymer. For chromium, a similar trend with molybdenum is followed but to a greater extent; with cross-linked sorbents all chromate previously sorbed is reduced to Cr(III), while with raw chitosan beads Cr(VI) reduction does not exceed 60%.

Copper uptake by ferric oxide and silica particles is studied through batch equilibrium and kinetic experiments under different conditions of pH and ionic strength. Acid–base titrations of the oxide particles indicate that the point of zero charge is 3.0 for the ferric oxide and 4.7 for the silica particles used in this study. For the same particles, electrokinetic measurements show an isoelectric point of 2.2 for ferric oxide and 2.7 for silica. The extent of metal removal is found to strongly depend on solution conditions and to increase with an increase in pH. Changes in ionic strength cause little or no significant change in the pH dependence of ion uptake. From control experiments, as well as from copper hydrolysis and speciation calculations, copper precipitation (as CuO) is evident above pH 6. In the acidic and neutral pH ranges, a marked increase in the ζ potential of both sorbents from baseline values is found during equilibrium copper uptake. Size distribution measurements show an increase in the number of flocculated sorbent particles at pH values corresponding to the steep increase in copper uptake. Further, at highly acidic pH ranges silica particles are found to be well stabilized and non-flocculating in equilibrium uptake studies. Similar findings are observed with ferric oxide particles at highly alkaline pH values. Kinetic studies indicate that copper uptake by ferric oxide is a much slower process as compared with uptake by silica under the conditions studied here. Also, the lower the sorbate/sorbent molar concentration ratio, the faster is the rate of copper uptake. With both particles, a rapid increase in ζ potential is observed within the first few minutes. Floc formation and breakage are evident from size distribution measurements. These findings indicate a possible role of metal ion uptake in particle flocculation kinetics through alteration of the ζ potential of sorbent particles.

A two-step magnetically seeded filtration process that includes heterogeneous flocculation (shear-flow and Brownian) and magnetic filtration is examined experimentally. The effects of various parameters — magnetic-field strength, size of particles, flow rate, seeding concentration, and solution pH — on the removal efficiency are investigated. A breakthrough model — which combines trajectory analysis, a particle buildup model, and a bivariate population-balance model applicable for Brownian flocculation — is developed to predict particle breakthrough in a magnetic filter. Experiments show that the removal efficiency increases as magnetic-field strength and particle size are increased and flow rate is decreased. A maximum in the removal efficiency is observed at a certain seeding concentration and at the lower pH values, which is explained from competing effects that take place with respect to magnetic susceptibility and size of aggregates as the seeding concentration and solution pH are increased. Modeling results of the trajectory analysis show that the effect of hydrodynamic resistance becomes important as Reynolds number and particle size are increased or the magnetic-field strength is decreased. Similarly to experimental observations, the modeling results predict that the removal efficiency increases with increasing magnetic-field strength and particle size indicating that the relative importance of magnetic and drag forces and the aggregation rate in the flocculation step play an important role in the magnetically seeded process. The breakthrough model developed in this study provides a good description of the experimental breakthrough data obtained from magnetic filtration of paramagnetic particles and magnetically seeded filtration with Brownian-flocculation.

The use of ozone in water and wastewater treatment systems has been shown to be a process that is limited by mass transfer. The most effective way to overcome this limitation is to increase the interfacial area available for mass transfer by decreasing the size of the ozone gas bubbles that are dispersed in solution. Electrostatic spraying (ES) of ozone into water was investigated in this work as a method of increasing the rate of mass transfer of ozone into a solution and thereby increasing the rate of phenol oxidation. The studies were conducted in a 30 cm column of 7.5 cm internal diameter, using deionized water and phenol as the solution phase and an ozone–oxygen mixture, generated by a corona-discharge ozone generator, as the gas phase. Results were obtained for ES at input power levels ranging from 0 to 4 kV and compared with two different pore-size bubble diffusers (10–15 μm and 40–60 μm). It was determined that the rate of mass transfer could be increased by as much as 40% when the applied voltage was increased from 0 to 4 kV as a result of the smaller bubbles generated by ES. In addition, ES was shown to be more effective than the medium-pore-size (10–15 μm) bubble diffuser; the best results were achieved at low gas flow rates. Phenol oxidation rates were also compared for ES and the medium-pore-size bubble diffuser, and the results indicate that the increased mass transfer rate achieved by ES enhances the rate of removal of phenol from solution.

Small gas bubbles are used in many environmental and industrial processes for solid-liquid separations or to facilitate heat and mass transfer between phases. Typically, smaller bubbles are preferred in treatment techniques due to both their high surface area-to-volume ratio and their increased bubble density at a fixed flow rate. This study examines some of the factors that affect the size of bubbles produced in the processes of electroflotation, dissolved air flotation, and a relatively new method known as electrostatic spraying. The effect of voltage, current and ionic strength was studied in electroflotation, the effect of pressure was studied in dissolved air flotation and the effect of voltage, capillary dimensions and flow rate was studied in electrostatic spraying. In electroflotation, the flow rate of gas produced increased as a function of voltage and current. Flow rate also increased as the ionic strength of the aqueous medium was increased. However, no clear trends in bubble size as a function of these parameters were evident. The bubbles produced in dissolved air flotation showed a decrease in size as saturation pressure was increased; however, the differences were insignificant at high pressures. Bubble size in electrostatic spraying decreased as voltage was increased. Finally, this study compares the three methods of bubble production in terms of average bubble diameter, bubble size distribution and power consumed during production. Dissolved air flotation produced the largest average bubble diameters, while electroflotation produced the smallest average bubble diameters. In terms of bubble size distribution, dissolved air flotation produced the most narrow distribution, electrostatic spraying produced the widest distribution, and electroflotation produced an intermediate distribution. In terms of power consumption, the pilot-scale dissolved air flotation system maximized surface area production, electroflotation produced an intermediate value, and electrostatic spraying of air produced the least surface area as a function of power consumed.

Magnetic seeding flocculation of micrometer-sized particles in liquid suspensions is investigated. Primary forces acting on individual particles, including gravity and magnetic attraction, as well as van der Waals, electrostatic, magnetic dipole, and hydrodynamic interparticle forces, are examined and quantified. A mathematical statement of the overall relative velocity is developed from the net force acting on a particle. From this, the equation of relative motion for two particles in cylindrical coordinates is derived. A computer model is then used to solve this equation repeatedly to find the particle trajectory borderline between collision and noncollision, thus determining the collision efficiency and collision frequency. The effects of a variety of parameters on flocculation performance are then explored. It is found that some factors have unexpected and complex influences on the collision efficiency and collision frequency, particularly the particle size ratio and the direction of the magnetic field.

Copper adsorption by granular activated carbon is reported in this paper. The experimental section includes titrations of activated carbon, as well as equilibrium and kinetic studies of copper adsorption. The potentiometric titration results show that the point of zero charge is 9.5, and that the surface charge increases with decreasing pH. The adsorption of copper strongly depends on solution pH and increases from 10 to 95% at pH ranging from 2.3 to 8. A dramatic increase in pH and emission of small gas bubbles are observed during the experiments, which may result from adsorption of hydrogen ion and/or reduction-oxidation reactions. The two-pK triple-layer model is employed to describe copper adsorption. KINEQL, an adsorption kinetics algorithm, is used to represent the experimental data, and it is found that the model can describe reasonably well the experimental measurements of surface charge, adsorption equilibrium, and adsorption kinetics. Calculations show that formation of the surface-metal complexes SO−Cu2+ and SO−CuOH+ (a hydrolysis product of SO−Cu 2+) in the outer layer around the surface of carbon results in removal of copper ion. It is also found that mass transfer controls the adsorption rate, and that adsorption occurs in the micropore region where both external mass transfer and diffusion are important.

The second part of KINEQL, which calculates adsorption rates under the condition that adsorption is controlled by mass transfer, is described in this article. The adsorption process is analyzed again in terms of three separate but interacting phenomena: surface ionization, complex formation, and the presence of an electrostatic double layer adjacent to adsorbent surfaces. A general form of a rate expression, suitable for transport-controlled cases, is formulated; this rate expression represents an approximate form of the intraparticle equation that has been found by other investigators to be very accurate for batch processes. Sample calculations demonstrating the use of the algorithm to calculate adsorption histories of cadmium on aluminum oxide are presented. Matching of experimental results with model calculations is obtained only after a combined macropore and micropore diffusion model is employed. In this model, macrodiffusion and microdiffusion act in parallel and independently. Reasonable values of the transport parameters are obtained in the case where only the simple metal ion diffuses into the interior of the adsorbents.

A general expression for the uptake of organic solutes from aqueous solutions by soil and sediment pellets in the Laplace domain is presented. This expression, together with the appropriate macroscopic conservation equation and initial and boundary conditions, provides a complete description of the movement and distribution of organic solutes through soil and subsurface systems. To obtain the numerical results for a specific system, the inversion from the Laplace domain into the time domain is required. In the present work, the use of two techniques, the fast Fourier transforms (FFT) and the Fourier series approximation (FSA), for inverting the Laplace transforms in connection with several problems concerning organic solute uptake by soils was explored. The FSA technique was found successful in all cases while the results by the FFT technique were strongly influenced by the selection of the algorithm parameters. In comparison with several numerical techniques for the direct solution of intraparticle diffusion equations, the FSA technique was found to have advantages in both accuracy and computational efficiency.