Residence Time Research Articles

Dual-functional adsorptive membranes for PFAS removal: Mechanism, CFD simulation, and selective enrichment

The remediation of emerging water contaminants, particularly per- and polyfluoroalkyl substances (PFAS), presents challenges due to their refractory nature and the presence of competing substances. Dual-functional adsorptive membranes, with hydrophobic backbone and quaternary ammonium moieties, were thereby designed to selectively intercept organic competitors while enrich PFAS. A 96.8 % removal of perfluorooctanoic acid (PFOA) was achieved and this effective removal (>90 %) maintained across five reuse cycles with a total treatment capacity of 650 L m−2. Rather than the rejection mechanism of nanofiltration process, these adsorptive membranes utilize synergistic electrostatic attraction and hydrophobic interactions, leading to a greater enrichment factor of 18.5 (PFOA over humic acid) and a permeability of 34.6 L m-2h−1 bar−1 (1.9- and 4.5-fold higher than reported NF 270 membranes, respectively). Furthermore, computational fluid dynamics (CFD) modeling revealed that the sponge-like matrix effectively prevents channeling flow and enhance access to adsorption sites. Sensitivity analysis and the high Damkohler number indicated that the adsorption process is mass transfer-controlled, with the key parameters ranked in order of significance: residence time > fluid viscosity > intrinsic adsorption rate. With consistent removal performance with co-existing competitors, efficient regeneration, and reusability, the dual-functional adsorptive membranes offer promising practical efficacy for PFAS remediation.

H2-Rich Gas Production from Gasification of Oily Sludge via Supercritical Water Technology: Synergy Effect of KOH, K2CO3, and Reaction Parameters

Yielding H2 as a sustainable gaseous fuel from oily sludge is of critical importance in mitigating the environmental effects linked with the usage of conventional fossil fuels. The deficiency in the drying of biomass has ensued to the exploration of supercritical water gasification (SCWG) as an effective method for harvesting H2-rich gas. This study utilized a combination of two alkali catalysts (KOH and K2CO3) in supercritical water to generate a H2-rich gas from a conventional oily sludge. The Box-Behnken design was utilized to assess the impact of different operational variables, including temperature (400-600°C), feed concentration (FC) (between 5 and 25 wt.%), residence time (RT) (15-45 min), and catalyst to feed mass ratios (FMR) (0-0.50). The maximum production of H2 at 3.22 mmolg-feed-1 was achieved under optimal conditions of 600°C, 32.76 min, and a KOH to FMR of 0.45 and K2CO3 to FMR of 0.28.

Optimizing waste heat recovery for hydrogen production: Modeling and simulation of ternary size metallic granule flow in a cooling cylinder

In order to recover the waste heat of high temperature metallic granules to produce steam for hydrogen production, a waste heat recovery cooling cylinder with cooling water channel is innovatively developed. The simulation is carried out based on DEM and soft sphere model to study the flow characteristics of ternary size metallic granules. The model of cooling cylinder is established and verified by comparing to the experiment data. The change rule of bed shape in the waste heat recovery cooling cylinder is examined, and the inclination angle, rotational speed and filling rate are assessed to find their influence on the flow characteristics of ternary size metallic granules. The results indicated that, with the increase of inclination angle, the axial velocity increases by 482.76%, which means the reduce of residence time of granules. With the increase of rotational speed, the axial velocity has an increase of 161.54%, the sum velocity increases by 158.49%, leading to a decrease of residence time. As the filling rate increases from 1.5% to 15.5%, the contact number has an increase of 91.53%, which lead to the increase of heat transfer area. The residence time and heat transfer area will directly affect the waste heat recovery efficiency, so a proper arrangement of granule flow is significant for enhancing the heat transfer efficiency.

Biofilm mass transfer and thermodynamic constraints shape biofilm in trickle bed reactor syngas biomethanation

Syngas (H2, CO2, CO) produced thermochemically from lignocellulosic biomass is an underexploited source for resource recovery and valorisation through its biological conversion for the production of a wide range of chemicals and fuels. Syngas biomethanation is one such promising bioconversion pathway, displaying interesting features such as high conversion efficiency and product selectivity, as methane is the sole product of the process. The biological conversion of syngas to high purity biomethane is still typically associated with a number of challenges related to the syngas composition, CO toxicity, and gas–liquid mass transfer limitations. In this work, the syngas biomethanation process carried out in trickle bed reactors was investigated at its boundary conditions to explore the limits of the process, focusing on syngas composition and mass-transfer conditions potentially limiting process performance. The process was found to be robust when exposed to CO excess, but highly sensitive to H2 excess, which caused severe inhibition even under small amounts of excess H2. This implies that biomethane purity comparable to natural gas can be achieved by addition of renewable H2, but this requires precise control to avoid process failure. Modulating the liquid recirculation rate and gas residence time allowed for a maximum methane productivity of 9.8 ± 0.5 mmol CH4 h−1 Lreactor−1 with full conversion of H2 and CO at a gas residence time of 1 h. Nevertheless, increasing the gas–liquid mass transfer with increasing liquid recirculation rate did not lead to increased methane productivity, which suggested additional rate-limiting bottlenecks in the process. Careful investigation of other factors potentially limiting the process led to the conclusion that diffusive transport of syngas components in the biofilm was the main bottleneck of the process. This diffusive limitation leads to a scenario of severe substrate scarcity in the biofilm phase that conditions the thermodynamic feasibility of the different biochemical reactions involved in syngas biomethanation. In turn, these thermodynamic constraints were found to drive the stratification of microbial groups and sequential consumption of syngas components along the height of the reactor

Employing stable isotopes to reveal temporal trajectories of water travelling through the soil–plant-atmosphere continuum

The spatiotemporal patterns of water travelling through the soil–plant-atmosphere continuum (SPAC) have received much attention due to the frequency of extreme weather and water scarcity. However, the interconnections and transboundary transport of specific compartments within the hydrologic cycle are poorly understood. We portrayed the propagation paths of water isotope signals by analyzing isotopes of precipitation, soil water, and xylem water. The isotope sine curves analysis method was improved to quantify water transfer efficiency, mean transmission time from precipitation to soil (MTT1), mean transmission time from soil to trees (MTT2), mean residence time within soil (MRTSW), and mean residence time within tree xylems (MRTXY). The temporal trajectory of water traveling through SPAC was depicted, and its influencing factors and intrinsic mechanisms were explored. Our results showed that (1) water isotopes were blocked when crossing water pools (precipitation, soil water, and xylem water) and the transfer efficiency was progressively weaker (85.5 %→13.5 %). (2) The MTT1 was significantly and positively correlated with soil porosity (Spearman correlation coefficient, 0.551). Its spatiotemporal pattern (0.8–15.9d) indicated that the transport and mixing of soil water involved two modes: displacement flow and bypass flow. The MTT2 (−13.2d–4.3d) of Platycadus orientalis was in general smaller than that of Quercus variabilis (−4.7d–11.5d). (3) The MRT (35.2d–343.8d) was influenced by a combination of soil physicochemical properties, root distribution, and tree morphological traits. Our study shows that connectivity between pools is better reflected with transfer efficiency. Comparing MTT and MRT of P. orientalis and Q. variabilis, tree hydrodynamic processes were quantified, and P. orientalis was more sensitive to seasonal moisture variability. Additionally, our study improved the understanding of the “black box” within the hydrological interface of plant-soil interactions.

Scheduling Dual-Arm Multi-Cluster Tools With Residency Time Constraints Beyond Swap-Based Strategies and Module-Bound Regions

Scheduling Dual-Arm Multi-Cluster Tools With Residency Time Constraints Beyond Swap-Based Strategies and Module-Bound Regions

Innovative Long-Acting Bisoprolol Patch: Synergistic Ion-Pair Skin Adsorption for Drug Delivery Control Coupled with Dynamic Modulation of Penetration Enhancers.

This study aims to develop a sustained release patch for bisoprolol (BSP) to address the issue of blood pressure fluctuations caused by traditional dosing methods, ensuring continuous drug release and efficient utilization. Long-chain saturated fatty acids (C6-C12) were chosen as counterions to precisely control BSP's permeation rate in the patch formulation, and the ion-pairing strategy's mechanism in drug delivery was thoroughly investigated. Molecular docking results revealed significant differences in the adsorption capacities of different ion pairs in the stratum corneum (SC) and epidermis, directly influencing their residence times and thereby regulating BSP's passive diffusion rate. Particularly, the BSP-C10 ion pair successfully reduced BSP's permeation rate to one-third of its baseline. To enhance drug delivery efficiency and reduce costs, chemical permeation enhancers (CPEs) are typically added to sustained release patches. In contrast to traditional static analyses based on cumulative permeation, this study utilized ATR-FTIR dynamic detection of isopropyl myristate (IPM) as a preferred enhancer, studying its disruptive effects on the skin barrier during drug delivery. The study observed that during drug delivery, the interaction between IPM and skin lipids follows a U-shaped trend: initially increasing, then decreasing, with the peak occurring at 10 h. Similarly, the drug delivery rate displays a comparable pattern. The addition of IPM as CPE increased the patch utilization rate from 39.8 ± 4.31 to 79.8 ± 7.27%. This strategy aims to rapidly reduce blood pressure in the initial phase with subsequent weakening of IPM disruption, allowing the ion-pairing strategy to dominate drug delivery control and maintain stable long-term therapeutic effects. Pharmacokinetic studies demonstrated that the newly developed BSP sustained release patch maintains stable blood drug concentrations, reduces burst release effects, increases bioavailability to 84.679%, doubles MRT0-t, halves Cmax, and significantly reduces the occurrence of blood pressure fluctuations.

Changes in integration and wellbeing by educational background among migrants in Kristiansand

Abstract Background Integration levels and wellbeing of newly arrived migrants change according to their everyday activities in their new home country. Although migrants have very different educational backgrounds and expectations regarding work in Norway, the compulsory educational activities are the same for all, disregarding their educational background. Aims To examine the changes in integration and wellbeing among newly arrived migrants participating in a compulsory integration program in Norway, according to their educational background. Methods As part of the Integration for Health project (I4H) we collected information from participants in Kristiansand municipality through a self-filled questionnaire in 2023 (N = 102) repeated six months apart, including questions from the Immigrant Policy Lab Index and the WHO-5 Well Being Index. For both screening tools, higher scores indicate better integration and wellbeing. Information on educational background was dichotomized into either health or non-health (natural and technical) sciences, using health sciences as the reference. We used generalized estimating equations to calculate relative risks (RR) with 95% confidence intervals (CI) adjusted for age and gender. Results The mean age was 34 years (SD 8.3) and 59% were women. Mean residency time was 3 years (SD 0.14). In terms of education, 14% had health sciences, and 86% had other educational backgrounds. We did not find change in wellbeing over the six-month period (RR 1.0 (95% CI 0.9-1.1), and this trend was similar for both educational groups (RR 0.9 (95% CI 0.8-1.1). Integration score slightly increased after six months (RR 1.0 (95% CI 1.0-1.1). However, there was no difference by educational background (RR 1.0 (95% CI 0.9-1.0). Conclusions Changes in wellbeing and integration among participants in the compulsory introductory program with short residency time, do not seem to vary by educational background in a six-month period. Key messages • Schools and introductory programs in the host country can be used as a arena to enhance both the integration and wellbeing of newly arrived migrants. • Strengthening migrants’ educational opportunities in the new host country is also of importance.

Air cleaner prototype: Reduction of airborne viruses and effects of UV-C irradiation on virus concentration and RNA copy numbers considering modeled residence times and doses

Air cleaner prototype: Reduction of airborne viruses and effects of UV-C irradiation on virus concentration and RNA copy numbers considering modeled residence times and doses

Gating residues govern ligand unbinding kinetics from the buried cavity in HIF-2α PAS-B.

While transcription factors have been generally perceived as "undruggable," an exception is the HIF-2 hypoxia-inducible transcription factor, which contains an internal cavity that is sufficiently large to accommodate a range of small-molecules, including the therapeutically used inhibitor belzutifan. Given the relatively long ligand residence times of these small molecules and the lack of any experimentally observed pathway connecting the cavity to solvent, there has been great interest in understanding how these drug ligands exit the buried receptor cavity. Here, we focus on the relevant PAS-B domain of hypoxia-inducible factor 2α (HIF-2α) and examine how one such small molecule (THS-017) exits from the buried cavity within this domain on the seconds-timescale using atomistic simulations and ZZ-exchange NMR. To enable the simulations, we applied the weighted ensemble path sampling strategy, which generates continuous pathways for a rare-event process [e.g., ligand (un)binding] with rigorous kinetics in orders of magnitude less computing time compared to conventional simulations. Results reveal the formation of an encounter complex intermediate and two distinct classes of pathways for ligand exit. Based on these pathways, we identified two pairs of conformational gating residues in the receptor: one for the major class (N288 and S304) and another for the minor class (L272 and M309). ZZ-exchange NMR validated the kinetic importance of N288 for ligand unbinding. Our results provide an ideal simulation dataset for rational manipulation of ligand unbinding kinetics.

Molecular dynamics insights into the dynamical behavior of structurally modified water in aqueous deep eutectic solvents (ADES).

Recent studies have demonstrated that the presence of water in deep eutectic solvents (DESs) significantly affects their dynamics, structure, and physical properties. Although the structural changes due to the addition of water are well understood, the microscopic dynamics of these changes have been rarely studied. Here, we performed molecular dynamics simulation of 30% (v/v) (∼0.57 molar fraction) water mixture of DES containing CH3CONH2 and NaSCN/KSCN at various salt fractions to understand the microscopic structure and dynamics of water. The simulated results reveal a heterogeneous environment for water molecules in aqueous DES (ADES), which is influenced by the nature of the cation. The diffusion coefficients of water in ADESs are significantly lower than that in neat water and concentrated aqueous NaSCN/KSCN solution. When Na+ ions are replaced by K+ ions in the ADES system, the diffusion coefficient increases, which is consistent with the measured nuclear magnetic resonance data. Self-dynamic structure factor for water and other simulated dynamic quantities, such as reorientation, hydrogen-bond, and residence time correlation functions, show markedly slower dynamics inside ADES than in the neat water and aqueous salt solution. Moreover, these dynamics become faster when Na+ ions in ADES are replaced by K+ ions. The results suggest that the structural environment of water in Na+-rich ADES is rigid due to the presence of cation-bound water and geometrically constrained water. The medium becomes less rigid as the KSCN fraction increases due to the relatively weaker interaction of K+ ions with water than Na+ ions, which accelerates the dynamical processes.

Improvement of Properties of Bio-Oil from Biomass Pyrolysis in Auger Reactor Coupled to Fluidized Catalytic Bed Reactor

The goal of this research work was to investigate the improvement of bio-oil issued from beechwood biomass through catalytic de-oxygenation. Pyrolysis was conducted in an auger reactor and the catalytic treatment was performed in a fluidized catalytic bed reactor. Lab-synthesized Fe-HZSM-5 catalysts with different iron concentrations were tested. BET specific surface area, BJH pore size distribution, and FT-IR technologies were used to characterize the catalysts. Thermogravimetric analysis was used to measure the amount of coke deposited on the catalysts after use. Gas chromatography coupled to mass spectrometry (GC-MS), flame ionization detection (GC-FID), and thermal conductivity detection (GC-TCD) were used to identify and quantify the liquid and gaseous products. The pyrolysis temperature proved to be the most influential factor on the final products. It was observed that a pyrolysis temperature of 500 °C, vapor residence time of 18 s, and solid residence time of 2 min resulted in a maximum bio-oil yield of 53 wt%. A high percentage of oxygenated compounds, such as phenolic compounds, guaiacols, and the carboxylic acid group, was present in this bio-oil. Catalytic treatment with the Fe-HZSM-5 catalysts promoted gas production at the expense of the bio-oil yield, however, the composition of the bio-oil was strongly modified. These properties of the treated bio-oil changed as a function of the Fe loading on the catalyst, with 5%Fe-HZSM-5 giving the best performance. A higher iron loading of 5%Fe-HZSM-5 could have a negative impact on the catalyst performance due to increased coke formation.

Boosting Photocatalytic Hydrogen Evolution by a Light Coupling and Charge Carrier Confinement Strategy

AbstractHigh‐performance photocatalysis requires efficient light absorption and low charge carrier recombination rates. Herein, a light coupling and charge carrier confinement strategy is demonstrated to simultaneously enhance the light absorption efficiency and suppress the charge carrier recombination for high‐performance photocatalysis. The strategy is achieved by the delicate incorporation of catalysts into a dual‐core‐shell structure (e.g., CdS@SiO2@NaYF4:Yb/Tm), in which CdS (catalyst), SiO2, and NaYF4:Yb/Tm serve as shell, outer core, and inner core, respectively. Interestingly, the absorbed light can be confined within the CdS layer through multiple reflections between the CdS and SiO2 interfaces, achieving light confinement. This confinement endows a longer light residence time, enhanced light reabsorption and reutilization efficacy, and a higher concentration of photogenerated charge carriers per unit of time. Moreover, the insulating SiO2 can confine the photogenerated charge carriers within CdS layer, thus shortening their diffusion length for reduced recombination rates. Notably, when employed as the photocatalyst, this dual‐core‐shell structure showed a superb photocatalytic hydrogen evolution rate up to 74.67 mmol g−1 h−1, which is 11 times higher than that of pristine CdS. This work provides a new strategy for the design and synthesis of high‐performance photocatalysts.

Modeling the interaction between powder particles and laser heat sources

This study investigates the spheroidization of titanium Ti-6Al-4V powder particles using numerical models developed in Abaqus and OpenFOAM. Spherical particles are crucial in powder-based additive manufacturing due to their superior flowability, packing density, and mechanical properties, enhancing printing precision and the quality of final products. While conventional techniques such as gas atomization and plasma spheroidization have been extensively researched, the potential of laser spheroidization remains underexplored. To address this gap, detailed numerical analyses of laser spheroidization were conducted, modeling heat transfer from the laser to powder particles using a transient uncoupled heat transfer method with latent heat considerations, while particle deformation was simulated with a phase-fraction-based interface-capturing approach integrated with Navier-Stokes equations. The results, validated against analytical models, indicate that particles within the 20–80 μm range experience optimal spheroidization within a 0.005-second residence time under laser heating, with particles smaller than 30 μm reaching evaporation temperatures of 5,000°C, while larger particles reshape without evaporating under a typical heat flux of 94 MW/m2 (1.8 kW laser power). This study demonstrates that laser spheroidization of Ti-6Al-4V powder can potentially increase powder yield by 10%, offering higher power density and shorter melting times compared to plasma spheroidization, thus presenting a more efficient alternative for achieving spherical particles of specific sizes.

Effects of Anisotropy, Convection, and Relaxation on Nonlinear Reaction-Diffusion Systems

The effects of relaxation, convection, and anisotropy on a two-dimensional, two-equation system of nonlinearly coupled, second-order hyperbolic, advection–reaction–diffusion equations are studied numerically by means of a three-time-level linearized finite difference method. The formulation utilizes a frame-indifferent constitutive equation for the heat and mass diffusion fluxes, taking into account the tensorial character of the thermal diffusivity of heat and mass diffusion. This approach results in a large system of linear algebraic equations at each time level. It is shown that the effects of relaxation are small although they may be noticeable initially if the relaxation times are smaller than the characteristic residence, diffusion, and reaction times. It is also shown that the anisotropy associated with one of the dependent variables does not have an important role in the reaction wave dynamics, whereas the anisotropy of the other dependent variable results in transitions from spiral waves to either large or small curvature reaction fronts. Convection is found to play an important role in the reaction front dynamics depending on the vortex circulation and radius and the anisotropy of the two dependent variables. For clockwise-rotating vortices of large diameter, patterns similar to those observed in planar mixing layers have been found for anisotropic diffusion tensors.

Hemodynamics simulation and analysis of left coronary artery aneurysms with concomitant stenosis

The hemodynamic parameters in arteries are difficult to measure non-invasively, and the analysis and prediction of hemodynamic parameters based on computational fluid dynamics (CFD) has become one of the important research hotspots in biomechanics. This article establishes 15 idealized left coronary artery bifurcation models with concomitant stenosis and aneurysm lesions, and uses CFD method to numerically simulate them, exploring the effects of left anterior descending branch (LAD) stenosis rate and curvature radius on the hemodynamics inside the aneurysm. This study compared models with different stenosis rates and curvature radii and found that as the stenosis rate increased, the oscillatory shear index (OSI) and relative residence time (RRT) showed a trend of increase; In addition, the decrease in curvature radius led to an increase in the degree of vascular curvature and an increased risk of vascular aneurysm rupture. Among them, when the stenosis rate was less than 60%, the impact of stenosis rate on aneurysm rupture was greater, and when the stenosis rate was greater than 60%, the impact of curvature radius was more significant. Based on the research results of this article, it can be concluded that by comprehensively considering the effects of stenosis rate and curvature radius on hemodynamic parameters, the risk of aneurysm rupture can be analyzed and predicted. This article uses CFD methods to deeply explore the effects of stenosis rate and curvature radius on the hemodynamics of aneurysms, providing new theoretical basis and prediction methods for the assessment of aneurysm rupture risk, which has important academic value and practical guidance significance.

Seafloor sediment characterization improves estimates of organic carbon standing stocks: an example from the Eastern Shore Islands, Nova Scotia, Canada

Abstract. Continental shelf sediments contain some of the largest stocks of organic carbon (OC) on Earth and play a vital role in influencing the global carbon cycle. Quantifying how much OC is stored in shelf sediments and determining its residence time is key to assessing how the ocean carbon cycle will be altered by climate change and possibly human activities. Spatial variations in terrestrial carbon stocks are well studied and mapped at high resolutions, but our knowledge of the distribution of marine OC in different seafloor settings is still very limited, particularly in dynamic and spatially variable shelf environments. This lack of knowledge reduces our ability to understand and predict how much and for how long the ocean sequesters CO2. In this study, we use high-resolution multibeam echosounder (MBES) data from the Eastern Shore Islands offshore Nova Scotia (Canada), combined with OC measurements from discrete samples, to assess the distribution of OC content in seafloor sediments. We derive four different spatial estimates of organic carbon stock: (i) OC density estimates scaled to the entire study region assuming a homogenous seafloor, (ii) interpolation of OC density estimates using empirical Bayesian kriging, (iii) OC density estimates scaled to areas of soft substrate estimated using a high-resolution classified substrate map, and (iv) empirical Bayesian regression kriging of OC density within areas of estimated soft sediment only. These four distinct spatial models yielded dramatically different estimates of standing stock of OC in our study area of 223 km2: 80 901, 58 406, 16 437 and 6475 t of OC, respectively. Our study demonstrates that high-resolution mapping is critically important for improved estimates of OC stocks on continental shelves and for the identification of carbon hotspots that need to be considered in seabed management and climate mitigation strategies.

Isotopic evidence of acetate turnover in Precambrian continental fracture fluids

The deep continental crust represents a vast potential habitat for microbial life where its activity remains poorly constrained. Organic acids like acetate are common in these ecosystems, but their role in the subsurface carbon cycle - including the mechanism and rate of their turnover - is still unclear. Here, we develop an isotope-exchange ‘clock’ based on the abiotic equilibration of H-isotopes between acetate and water, which can be used to define the maximum in situ acetate residence time. We apply this technique to the fracture fluids in Birchtree and Kidd Creek mines within the Canadian Precambrian crust. At both sites, we find that acetate residence times are <1 million years and calculated a rate of turnover that could theoretically support microbial life. However, radiolytic water-rock reactions could also contribute to acetate production and degradation, a process that would have global relevance for the deep biosphere. More broadly, our study demonstrates the utility of isotope-exchange clocks in determining residence times of biomolecules with possible applications to other environments.

Cooperative multi-agent reinforcement learning for multi-area integrated scheduling in wafer fabs

The existing scheduling methods of wafer fabs focus on single area, achieving local optimisation while failing to realise global optimisation due to neglecting the coordination of multi-area. Therefore, it is necessary to consider the complex opposing relationships between multi-area caused by constraints such as batch processing, re-entrance, and multiple residency times within and between areas to conduct integrated scheduling and shorten the production cycle time. For this issue, this paper proposes a cooperative multi-agent reinforcement learning for multi-area integrated scheduling. Aiming at the dynamic batching and scheduling considering the dynamic arrival lots in multi-area, a multi-agent reinforcement learning algorithm is presented to learn the optimal dynamic batching and scheduling policy firstly. Subsequently, a cooperative multi-agent framework is raised to achieve the global optimisation and coordination of multi-area. Furthermore, an adaptive exploration strategy is constructed to enhance the global exploration capability of the complex solution space caused by residency time constraints and re-entrant property. Moreover, a policy share enhanced Double DQN is employed to improve the generalisation and adaptability of the multi-agent. Finally, the experiments demonstrate that the proposed integrated scheduling method has better comprehensive performance compared to the previous area-separated scheduling methods.

Uranium removal from contaminated groundwater using goethite-loaded composite microporous membrane

In this study, we have coupled adsorption and membrane separation for the removal of uranium from contaminated groundwater in environmentally relevant conditions at low energy requirements. This study mainly focuses on elucidating uranium, U(VI), adsorption mechanisms using surface complexation modeling approach in a novel goethite-loaded composite microfiltration membrane (GLM). This experiment involved immobilizing goethite nanorods in a microporous (0.22 μm pore size) poly (vinylidene fluoride) (PVDF) membrane. The effect of varying goethite loading and hydraulic residence time on U(VI) removal was investigated at field-relevant pH (i.e. pH 8.5). U(VI) adsorption (i.e. 4.95 μg·mg−1) was optimum at a goethite loading 1.20 mg·cm−2. The effect of varying hydraulic residence time had no impact on U(VI) removal which was also confirmed via performing batch adsorption kinetic experiments. GLM membrane loaded at 1.2 mg·cm−2 could treat 275 L of U(VI) contaminated water having 200 μg of U L−1 below WHO drinking water limit (i.e. 30 μg of U L−1) with 1 m2 of membrane surface area with a adsorption capacity of 6.12 μg·mg−1. Varying the pH of aqueous solution, containing U(VI) from pH 4.0 to pH 10.0, showed a significant impact on uranium uptake ranging from 0.7 μg·mg−1 to 2.63 μg·mg−1 by the composite membrane. The adsorption mechanism of uranium onto goethite was explained via the formation of bidentate surface complexes using the Surface Complexation Model (SCM). The results of batch pH edge experiments and SCM have been compared with pH experiments performed using GLM. The results of SCM predicted the batch pH edge experiment within a RMSE of 0.055. The trend of U(VI) removal in membrane experiments was observed to be similar to that of batch pH edge experiments and was well predicted SCM model. Our results showed that the novel goethite-loaded membrane has the potential for the effective removal of uranium with a lower specific energy consumption.