Reduced Membrane Area Research Articles

Experimental Study on Ion Transport in Microfluidic Electrodialysis Using Partially Masked Ion Exchange Membranes.

Electrodialysis using anion-exchange membranes (AEMs) and cation-exchange membranes (CEMs) has been widely used for water desalination and the management of various ionic species. During commercial electrodialysis, the available area of an ion-exchange membrane is reduced by a non-conductive spacer that is in contact with the AEM/CEM. Although multiple reports have described the advantages or disadvantages of spacers, fewer studies have explored the effects of spacers on the mass transport effect of the reduced membrane area excluding the fluid flow change. In this paper, we present our experimental studies concerning mass transport in microfluidic electrodialysis systems with partially masked ion-exchange membranes. Six different types of masking membranes were prepared by the deposition of non-conductive films on parts of the membranes. The experimental results showed that the overlapped types (in which masking was vertically aligned in the AEM/CEM) exhibited a larger electrical conductance and better current/energy efficiency, compared with the non-overlapped types (in which masking was vertically dislocated in the AEM/CEM). We also observed that a reduction in the unit length of the unmasked ion-exchange membrane enhanced overall mass transport. Our results demonstrate the effects of patterned membranes on electrical resistance and desalination performance; they also identify appropriate arrangements for electromembrane systems.

Desalination of Polymer-Flooding Produced Water at Increased Water Recovery and Minimized Energy

When desalinating an industrial stream like polymer-flooding produced water via electrodialysis (ED), high water recoveries, low energy consumption, and reduced membrane area are all desirable. However, little effort has been done until now to experimentally achieve these goals. Encouraged by recent and promising results obtained using aliphatic membranes and pulsed electric field, this study experimentally evaluated different strategies and operational conditions to increase the water recovery while keeping a low energy consumption. The results obtained were analyzed to understand the trade-offs in operative time, water recovery, and energy consumption. Finally, the experimental data was employed to perform an economic analysis, which indicated that although further optimization should be possible, current conditions already make ED desalination of polymer-flooding produced water a sound case from an economical point of view.

Optimization and heat integration of hybrid R–HIDiC–PV process with the series–parallel arrangement of PV modules and recycle streams for TAME production

Tert–amyl methyl ether (TAME) production process is consisted of a reactor, a reactive distillation (RD) column and the methanol recovery section. The bottom product of the RD column is TAME while the distillate is consisted of the azeotropic mixture of methanol and isopentane (i-pentane) that can be separated by either the pervaporation (PV) membrane or conventional pressure swing distillation (PSD) and extractive distillation (ED) methods. The PV process allows the use of both series and parallel arrangements. The series arrangement has a lower membrane area compared to the parallel arrangement, while the parallel arrangement has a lower energy cost. A series–parallel arrangement with recycle streams was used in the present study to take advantage of both the series and parallel arrangements. The HIDiC method was used for reducing energy consumption in the RD column. Moreover, heat integration between PV streams and internal flows in the RD column was used to reduce PV energy consumption. The number of modules in each row, the recycle stream, the heat exchange ratio between the rectifying and stripping sections in the RD column and the heat exchange ratio between PV streams and internal RD streams were obtained by a hybrid GA–PSO algorithm. Furthermore, all RD and PV parameters were considered optimization variables and most importantly, all process variables were optimized simultaneously. According to the results, the proposed process reduced the total annual cost (TAC) by 52% and led to a 57% energetic gain compared to the conventional hybrid RD–PSD process. The proposed process also reduced TAC by 48% and led to a 40% energetic gain in comparison with the hybrid RD–PV process. This can be related to the reduced membrane area compared to the series and parallel arrangements as well as reduced energy costs of PV heaters through heat integration between PV steams and internal flows of the column.

Forward osmosis membrane modular configurations for osmotic dilution of seawater by forward osmosis and reverse osmosis hybrid system

This study evaluates various options for full-scale modular configuration of forward osmosis (FO) process for osmotic dilution of seawater using wastewater for simultaneous desalination and water reuse through FO-reverse osmosis (RO) hybrid system. Empirical relationship obtained from one FO membrane element operation was used to simulate the operational performances of different FO module configurations. The main limiting criteria for module operation is to always maintain the feed pressure higher than the draw pressure throughout the housing module for safe operation without affecting membrane integrity. Experimental studies under the conditions tested in this study show that a single membrane housing cannot accommodate more than four elements as the draw pressure exceeds the feed pressure. This then indicates that a single stage housing with eight elements is not likely to be practical for safe FO operation. Hence, six different FO modular configurations were proposed and simulated. A two-stage FO configuration with multiple housings (in parallel) in the second stage using same or larger spacer thickness reduces draw pressure build-up as the draw flow rates are reduced to half in the second stage thereby allowing more than four elements in the second stage housing. The loss of feed pressure (pressure drop) and osmotic driving force in the second stage are compensated by operating under the pressure assisted osmosis (PAO) mode, which helps enhance permeate flux and maintains positive pressure differences between the feed and draw chamber. The PAO energy penalty is compensated by enhanced permeate throughput, reduced membrane area, and plant footprint. The contribution of FO/PAO to total energy consumption was not significant compared to post RO desalination (90%) indicating that the proposed two-stage FO modular configuration is one way of making the FO full-scale operation practical for FO-RO hybrid system.

An Enhanced Spring-Particle Model for Red Blood Cell Structural Mechanics: Application to the Stomatocyte-Discocyte-Echinocyte Transformation.

Red blood cells (RBCs) are the most abundant cellular element suspended in blood. Together with the usual biconcave-shaped RBCs, i.e., discocytes, unusual-shaped RBCs are also observed under physiological and experimental conditions, e.g., stomatocytes and echinocytes. Stomatocytes and echinocytes are formed from discocytes and in addition can revert back to being discocytes; this shape change is known as the stomatocyte-discocyte-echinocyte (SDE) transformation. To-date, limited research has been conducted on the numerical prediction of the full SDE transformation. Spring-particle RBC (SP-RBC) models are commonly used to numerically predict RBC mechanics and rheology. However, these models are incapable of predicting the full SDE transformation because the typically employed bending model always leads to numerical instability with severely deformed shapes. In this work, an enhanced SP-RBC model is proposed in order to extend the capability of this model type and so that the full SDE transformation can be reproduced. This is achieved through the leveraging of an advanced bending model. Transformed vesicle and RBC shapes are predicted for a range of reduced volume and reduced membrane area difference (MAD), and very good agreement is obtained in the comparison of predicted shapes with experimental observations. Through these predictions, vesicle and SDE transformation phase diagrams are developed and, importantly, in the SDE case, shape boundaries are proposed for the first time relating RBC shape categories to RBC reduced volume and reduced MAD.

Kinetic Study of Photo-Induced Lipid Oxidation in Giant Unilamellar Vesicles

Despite association of lipid oxidation to many key clinical concerns, the specific molecular mechanisms and dynamics of its roles in etiology and pathogenesis are not well understood. We have studied the kinetics of photo-induced phospholipid bilayer oxidation using giant unilamellar vesicles (GUVs) as model membranes. Incorporating rhodamine-labeled 1,2-dipalmitoyl-sn-glycero-3-phosphoethanoamine (Rh-DPPE) as photosensitizer to generate highly reactive singlet oxygen at the surface of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) GUVs, we observed several morphological changes during oxidation of the monounsaturated lipid bilayer. Within minutes of irradiation, the initial and brief growth of membrane area was accompanied by vesicle flattening and high-amplitude membrane fluctuations. After reaching a maximum area, the membrane began contracting, causing the GUVs to become tumid with a surface tension sufficient to exceed the critical limit for pore formation. The periodic micron-scale openings of pores could be quantitatively observed as step-decreases in vesicle size beyond pre-oxidation dimensions. The growth and shrinkage behaviors were analyzed as consecutive first-order rate-limiting steps within the overall oxidative process to estimate molecular size changes and the rate constants of the underlying chemical events. Dependence of these constants on irradiation intensity and on concentrations of Rh-DPPE and DOPC were considered. Furthermore, experiments varying membrane DOPC content were repeated at ten-fold increased aqueous viscosity to slow down fluid leakage and allow for more accurate measurement of pore closure rates. The calculated decreased line tension with higher DOPC concentration suggested pore edge-stabilizing geometry of oxidation products. In agreement with existing simulation results, we observed that photo-induced lipid oxidation consecutively expanded and reduced membrane area of DOPC GUVs, and our analysis suggested that these actions resulted from two key reaction steps occurring at different rates.

The cost of a large-scale hollow fibre MBR

A cost sensitivity analysis was carried out for a full-scale hollow fibre membrane bioreactor to quantify the effect of design choices and operational parameters on cost. Different options were subjected to a long term dynamic influent profile and evaluated using ASM1 for effluent quality, aeration requirements and sludge production. The results were used to calculate a net present value (NPV), incorporating both capital expenditure (capex), based on costs obtained from equipment manufacturers and full-scale plants, and operating expenditure (opex), accounting for energy demand, sludge production and chemical cleaning costs. Results show that the amount of contingency built in to cope with changes in feedwater flow has a large impact on NPV. Deviation from a constant daily flow increases NPV as mean plant utilisation decreases. Conversely, adding a buffer tank reduces NPV, since less membrane surface is required when average plant utilisation increases. Membrane cost and lifetime is decisive in determining NPV: an increased membrane replacement interval from 5 to 10 years reduces NPV by 19%. Operation at higher SRT increases the NPV, since the reduced costs for sludge treatment are offset by correspondingly higher aeration costs at higher MLSS levels, though the analysis is very sensitive to sludge treatment costs. A higher sustainable flux demands greater membrane aeration, but the subsequent opex increase is offset by the reduced membrane area and the corresponding lower capex.

Influence of operation parameters on the separation of mixtures by pervaporation and vapor permeation with inorganic membranes. Part 1: Dehydration of solvents

The separation performance of two different commercially available tubular inorganic membranes was studied for solvent dehydration. The separation layers consisted of A-type zeolite and microporous silica. The membrane characteristics were determined as function of operating conditions such as feed composition, temperature, and permeate pressure in pervaporation and vapor permeation. Among different membranes of the same batch, flux and selectivity were reproducible within 10%. The partial flux of water as the preferentially permeating component increases linearly with the water vapor pressure difference between feed and permeate and depends only marginally (viscosity influence) upon the properties of the organic component. The flux of the organic (retained) component is low and can best be described by assuming a substance and membrane specific permeance (flux over partial pressure difference) that is independent of composition. At very low water concentration in the feed one would expect a strong increase in permeability of the retained component through non-zeolite pores and larger silica pores as predicted by pure component measurements. However, this effect was not observed in mixtures within the concentration range studied here. A temperature rise improves flux rates exponentially while selectivity remains high. Thus, higher module cost in comparison to polymeric membranes can be compensated by reduced membrane area if a higher operating temperature can be chosen. Flux and selectivity decline as a function of permeate pressure with decreasing driving force. In vapor permeation with inorganic membranes superheating of the vaporous feed improves their performance while for polymeric materials a steep flux decline is observed. High flux and selectivity are obtained in the separation of water from alcohols. The normalized flux values of the A-type zeolite membrane are roughly 10 kg/m 2 h bar with a mixture selectivity of 2000 for methanol, 4000 for ethanol and 8000 for n -butanol. The average permeance of the amorphous silica membrane lies above 12 kg/m 2 h bar with mixture selectivity of 50 for methanol, 500 for ethanol and 2000 for n -butanol. The separation mechanism is mainly based on adsorption and diffusion enhanced by shape selectivity and size exclusion in some cases. The transport characteristics could be described with a simple transport model based on normalized permeate fluxes. With regard to the operation stability of the membranes, no deterioration of the performance was observed for the A-type zeolite in solvent dehydration or in separation of water from reaction mixtures. The silica membrane showed an initial conditioning effect involving a rearrangement of Si–OH groups with an increase in selectivity and decrease in flux of about 30%. After a few hours the performance stabilized and remained constant during further operation.

Membrane fluidity and lipid content of human spermatozoa selected by swim‐up method

In this work, we examined whether spermatozoa (spz) from normospermic fertile patients and selected by a swim‐up (S‐U) procedure had a particular membrane fluidity related to their maturity and their lipid content as compared with the sperm cells from the whole ejaculate (total sperm). Swim‐up selected sperm had a reduced cytoplasmic space as revealed by a lower creatine kinase (CK) activity compared with total sperm (2 ± 1 vs. 12 ± 5 mUI/107 spz, p < 0.05). The cholesterol (Chol) and total phospholipid (PL) contents were significantly lower in S‐U selected sperm than in total sperm (0.72 ± 0.08 vs. 1.20 ± 0.30 nmol/106 spz for Chol and 1.77 ± 0.17 vs. 2.78 ± 0.50 nmol/106 spz for PL, p < 0.05) and such a decrease was observed for the three major membrane PL: phosphatidylethanolamine (PE), phosphatidylcholine (PC) and sphingomyelin (SM). However, these decreases were not associated with a change in either Chol/PL or PC/(PC + PE) molar ratios. Membrane fluidity estimated by fluorescence polarization remained comparable between the S‐U sperm fraction and total sperm (fluorescence polarization anisotropy, r, which is inversely proportional to the fluidity: 0.235 ± 0.006 vs. 0.230 ± 0.005). The sperm membrane fluidity obtained in normospermic patients was compared with abnormospermic ones (oligoasthenoteratospermia). In abnormospermic patients, the membrane fluidity was decreased in migrated spermatozoa compared with total sperm (anisotropy: 0.210 ± 0.010 vs. 0.250 ± 0.013, p < 0.01). Our data suggest that the S‐U method selected a subpopulation of mature spermatozoa characterised by a low content of Chol and PL, likely related to a reduced membrane area. The fact that Chol/PL and PC/(PC + PE) molar ratios were unchanged shows a maintenance of the membrane quality. This was confirmed by the fluorescence anisotropy measurement showing no difference in plasma membrane fluidity between S‐U selected sperm and total sperm. In abnormal semen the migrated spermatozoa had a lower fluidity compared with total sperm suggesting a defective sperm function. These results bring new elements characterizing the S‐U selected spermatozoa.

Potassium Current Development and its Linkage to Membrane Expansion During Growth of Cultured Embryonic Mouse Hippocampal Neurons: Sensitivity to Inhibitors of Phosphatidylinositol 3-Kinase and Other Protein Kinases

Hippocampal pyramidal neurons express three major voltage-dependent potassium currents, IA, ID, and IK. During hippocampal development, IA, the rapidly activating and inactivating transient potassium current, is detected soon after pyramidal neurons can be morphologically identified. Appearance of IA in developing pyramidal neurons is dependent on contact with cocultured astroglial cells; cultured pyramidal neurons not in contact with astroglial cells have reduced membrane area and IA (Wu and Barish, 1994). We have examined intracellular signaling pathways that could contribute to the regulation of IA development by probing developing pyramidal neurons with kinase inhibitors. We observed that exposure to LY294002 or wortmannin, inhibitors of phosphatidylinositol (PI) 3-kinase, reduced somatic cross-sectional area, neurite outgrowth, whole-cell capacitance, IA amplitude and density (amplitude normalized to membrane area), and immunoreactivity for Kv4.2 and/or Kv4.3 (potassium channel subunits likely to be present in the channels carrying IA). In contrast, exposure to ML-9 or KN-62, inhibitors of myosin light chain kinase or Ca2+-calmodulin-dependent protein kinase II (CaMKII), reduced membrane area and IA amplitude but did not affect IA density or Kv4. 2/3 immunoreactivity to the same extent as inhibitors of PI 3-kinase. Unexpectedly, exposure to bisindolymaleimide I or calphostin C, inhibitors of protein kinase C (PKC), did not affect membrane area or potassium current development. Our data suggest that PI 3-kinases regulate both A-type potassium channel synthesis and plasmalemmal insertion of vesicles bearing these potassium channels. CaMKII appears to regulate fusion of channel-bearing vesicles with the plasmalemma and myosin light chain kinase to regulate centripetal transport of channel-bearing vesicles from the Golgi. We further suggest that astroglial cells exert their influence on pyramidal neuron development through activation of PI 3-kinases.

Development of a pilot‐scale microfiltration harvest for the isolation of physostigmine from Streptomyces griseofuscus broth

AbstractA pilot‐scale microfiltration harvest was developed for the isolation of physostigmine from a mycelial fermentation broth. Complete permeation for this extracellular secondary metabolite was obtained during initial laboratory screening with a variety of crossflow filtration membranes but poor filtration flux made process feasibility uncertain. Modification of the fermentation medium improved fluxes from 10–20 dm3 m−2 h−1 to 60–80 dm3 m−2 h−1 which significantly reduced membrane area requirements, making the process feasible for larger scale implementation. A commercially‐available ceramic membrane with 0·2 μm pores was employed for the scale‐up of this step to the pilot plant; this membrane was found to provide flux similar to that of polymeric membranes and had superior regeneration characteristics. Optimum performance at bench scale was obtained using 70 kPa transmembrane pressure and 4·0 m s−1 crossflow velocity. The mycelial broth had a very high suspended solids concentration (30% (v/v)) which limited us to a two‐fold concentration before starting the diafiltration washes. The process was scaled‐up to the 200–400 dm3 scale, with good reproducibility and excellent membrane regenerability observed in a series of five experiments. An increase in membrane loading did result in a decreased average flux at the larger scale (47·6 dm3 m−2 h−1), which indicated the importance of this parameter. A centrifugal pump was substituted for a positive displacement pump upon scale‐up and performed well if provided with the appropriate suction head. Scale‐up in general was straightforward, provided proper attention was given to the hydraulic design of the system.

Variable clinical severity of hereditary spherocytosis: Relation to erythrocytic spectrin concentration, osmotic fragility, and autohemolysis

To determine whether stratifying hereditary spherocytosis by degree of severity could provide guidelines regarding which patients would benefit from splenectomy, we evaluated the clinical characteristics of 80 patients (63 children) and 27 healthy relatives. In addition to routine hematologic determinations, osmotic fragility, autohemolysis, erythrocyte spectrin content, and erythrocyte membrane lipid phosphorus were measured and correlated with the disease severity. Four categories were identified: (1) spherocytosis as a trait in symptom-free relatives of patients with recessively inherited disease; (2) mild and (3) moderate spherocytosis, largely observed in patients with dominantly inherited disease; and (4) severe spherocytosis, observed in only two patients, who were characterized by recessive inheritance and transfusion dependence. By the identification of carriers, a recessive mode of inheritance could be demonstrated in 20% of the families with spherocytosis. The erythrocyte spectrin concentration was normal in carriers and patients with mild spherocytosis, and was significantly reduced in the moderate and severe states of the disease. This difference was not accounted for by reduced membrane area of the cells, as measured by the phospholipid concentration per cell. We conclude that patients with mild spherocytosis usually do not require splenectomy during childhood and adolescence; patients with moderate or severe disease should have splenectomy. Patients with severe spherocytosis have a partial response to splenectomy but a considerable degree of increased hemolysis persists. Most patients with less than 80% of normal spectrin content require splenectomy.