Standard Blocking Research Articles

Treatment of Oily Waste Water Using Low-Cost Ceramic Membrane: Flux Decline Mechanism and Economic Feasibility

This work addresses the applicability of different membrane pore blocking models for the prediction of flux decline mechanisms during dead end microfiltration (MF) of stable oil-in-water (o/w) emulsions using relatively low-cost ceramic membranes. Circular disk type membranes (52.5 mm diameter and 4.5 mm thickness) were prepared by the paste method using locally available low-cost inorganic precursors such as kaolin, quartz, calcium carbonate, sodium carbonate, boric acid, and sodium metasilicate. Characterization of the prepared membrane was done by SEM analysis, porosity determination, and pure water permeation through the membrane. Hydraulic pore diameter, hydraulic permeability, and hydraulic resistance of the membrane was evaluated as 0.7 µm, 1.94 × 10−6 m3/m2·s·kPa and 5.78 × 1011 m2/m3, respectively. The prepared membrane was used for the treatment of synthetic stable o/w emulsions of 40 and 50 mg/L crude oil concentration in batch mode with varying trans-membrane pressure differentials ranging from 41.37 to 165.47 kPa. The membrane exhibited 96.97% oil rejection efficiency and 21.07 × 10−6 m3/m2·s permeate flux after 30 min of experimental run at 165.47 kPa trans-membrane pressure for 50 mg/L oil concentration. Different pore blocking, models such as complete pore blocking, standard pore blocking, intermediate pore blocking and cake filtration were used to gain insights into the nature of membrane fouling during permeation. The observed trends for flux decline data convey that the decrease in permeate flux was initially due to intermediate pore blocking (during 1 to 10 minutes of experimental run) followed with cake filtration (during 10 to 30 minutes of experimental run). Based on retail prices of the inorganic precursors, the membrane cost was estimated to be 130 $/m2. Finally, preliminary process economic studies for a single stage membrane plant were performed for the application of the prepared membrane in industrial scale treatment of o/w emulsions. A process economics study inferred that the annualized cost of the membrane plant would be 0.098 $/m3 feed for treating 100 m3/day feed with oil concentration of 50 mg/L.

Effect of biofiltration as pretreatment on the fouling of nanofiltration membranes

The effect that biofiltration had on the fouling behaviour of several commercial nanofiltration (NF) membranes used for drinking water treatment was investigated using a bench-scale set-up. A dual-media anthracite-sand biofilter was used to pretreat a humic acid-laden solution spiked with a solution of pharmaceutically active compounds and for each membrane type, the performance using the effluent of the biofilter as feedwater was compared to membrane performance in the absence of pretreatment. Chemical, microbiological, and morphological analyses were carried out to evaluate the fouling performance of the membranes. A slight decrease in the organic carbon and the viable counts (measured as heterotrophic plate counts) deposited on the membrane was observed in all cases where biofiltration was used as pretreatment. The smallest organic fraction was able to get inside the pores of the looser NF membrane causing standard blocking. Biofiltration was able to considerably reduce the rate of flux decline to one third or less of that decline observed with the membranes that did not have pretreatment.

Metabolic Stress Induces the Lysosomal Degradation of Neuropilin-1 but Not Neuropilin-2

The neuropilins-1 and -2 (NRP1 and NRP2) function as receptors for both the semaphorins and vascular endothelial growth factor. In addition to their contribution to the development of the nervous system, NRP1 and NRP2 have been implicated in angiogenesis and tumor progression. Given their importance to cancer and endothelial biology and their potential as therapeutic targets, an important issue that has not been addressed is the impact of metabolic stress conditions characteristic of the tumor microenvironment on their expression and function. Here, we demonstrate that hypoxia and nutrient deprivation stimulate the rapid loss of NRP1 expression in both endothelial and carcinoma cells. NRP2 expression, in contrast, is maintained under these conditions. The lysosomal inhibitors chloroquine and bafilomycin A1 prevented the loss of NRP1 expression, but proteasomal inhibitors had no effect. The hypothesis that NRP1 is degraded by autophagy is supported by the findings that its expression is lost rapidly in response to metabolic stress, prevented with 3-methyladenine and induced by rapamycin. Targeted depletion of NRP2 using small hairpin RNA revealed that NRP2 can function in the absence of NRP1 to mediate endothelial tube formation in hypoxia. Studies aimed at assessing NRP function and targeted therapy in cancer and angiogenesis should consider the impact of metabolic stress.

Sterilizing filtration—Principles and practice for successful scale-up to manufacturing

Filtration process design using micro-filtration membranes includes the proper sizing and scale-up of filtration units and requires an understanding of the effects of membrane fouling on filter capacity. This fouling is usually quantified by some fouling factor K. The filter capacity (related to surface area A) also impacts the rate of filtration which is usually quantified by the initial normalized flux through the filter J 0. For ideally scalable systems, the normalized flux J 0 should be the same for filtration across the same membranes with different surface area. Since fittings and device design can significantly affect filter resistance, scale-up factors must be taken into account in designing a scalable filtration step. In this manuscript we describe the principal approach and tools utilized to successfully transfer the sterile membrane filtration process for a pharmaceutical product from laboratory through pilot plant to manufacturing. Generalized models of pore fouling based on the standard blocking or complete blocking mechanisms are derived to simulate filtration of solutions at different filter set-up configurations using filters of different filter areas and construction. The analysis shows that specific resistance of filters resulting from differences in construction, and resistances of other flow details must also be considered in scale-up. Three different scales are compared to illustrate the application of the models to evaluation of filtration data and to the scale-up of filtration for a pharmaceutical solution. Millipore hydrophilic PVDF sterilizing filters were used at all scales. Scale-up criteria based on surface area (filter capacity) and flow rate (filtration duration) were employed at different scales. The case study results confirm that successful scale-up of filtration of pharmaceutical products requires understanding and correct prediction of both, the fouling characteristics (impacted mostly by properties and interactions between solution and membrane) and the flow characteristics (impacted by the filter construction and by the filtration system configuration).

Filtration characteristics in dead-end microfiltration of living Saccharomyces cerevisiae cells by alumina membranes

Dead-end microfiltration of live Saccharomyces cerevisiae (yeast) suspensions of low concentration was carried out in a stirred membrane cell and corresponding permeate flux as a function of trans-membrane pressure (TMP) and membrane pore size were estimated. The deposition mechanism on the membrane surface and/or into its porous structure was analyzed in terms of various kinetic models, viz., cake filtration, standard blocking and complete pore-blocking models. It was seen that an initial intense flux decline due to external blockage followed by an internal deposition (partially retained cells) or the formation of a cake. Steady state permeate fluxes increased with the increase in the pore size of the membranes and decreased with the increase in yeast concentrations. In the present study, linear regression analysis of the filtration data showed that β values (filtration characteristic constant) were in the same order of magnitude as those of theoretical values. It was found that specific cake resistance increased with the increase in the TMP. The β values were found to vary in the range of –0.5 to 1.4. Compressibility factor (n) was found to be 0.853. According to the values, it has been found that all the above filtration mechanisms were simultaneously occurring rather than contributing individually.

Depth filtration approach to the theory of standard blocking: Prediction of membrane permeation rate and selectivity

A macroscopic depth filtration theory for the standard blocking of the pores of UF/MF membrane is developed. The theory predicts the membrane permeation rate and selectivity based on the introduction of the classical filter coefficient and shows that the profile of the number of deposited particles over the pore length is highly nonuniform (steep), descending to the pore outlet. It is shown that the conventional standard blocking theory based on the uniform-profile assumption cannot adequately describe the variation of permeation rate with time for highly selective membranes and therefore should not be used in processing the experimental data. The adequate description of standard blocking can be obtained with simple analytical formulas derived on the basis of the developed depth filtration theory and the simplified model in which the actual steep profile is replaced by a stepwise profile of deposited particles. Comparison with experimental data showed a high accuracy of the proposed calculation formulas.

Applicability of the exponential time dependence of flux decline during dead-end ultrafiltration of binary protein solutions

Flux decline in the dead-end ultrafiltration (UF) of binary solutions of bovine serum albumin (BSA, pI 4.7, MW 67,000) and hemoglobin (Hb, pI 7.1, MW 68,000) with polyethersulfone (PES, 100 kDa) and polyacrylonitrile (PAN, 100 kDa) membranes was studied. Key factors affecting the flux decline including solution pH (6.00–7.50), total protein concentration (1.5–9.0 μM), transmembrane pressure (TMP, 10–50 psi), and ionic strength (0.01–0.1 M) were systematically investigated. It was shown that the blocking filtration law could satisfactorily analyze the flux decline behavior. A simplified exponentially time-dependent model was adopted to describe the dynamics of flux decline during UF process, and used to determine the adequate time for membrane cleaning. The mechanism of membrane fouling was also analyzed by blocking filtration law, in which the standard blocking always dominated at the early stage in such UF processes. The fouling mechanism strongly depended on hydrophobic characteristics of the membranes, concentration and charge of the proteins, as well as pH and ionic strength of the solutions.

Analysis of filtration characteristics in submerged microfiltration for drinking water treatment

Hollow fiber membranes have been widely employed for water and wastewater treatments. Nevertheless, understanding the filtration characteristics of hollow fiber membranes is complicated by the axial distributions of transmembrane pressure (TMP) and flux, which are key factors for both fouling control and module design. In this study, model equations to account for different fouling mechanisms were derived to analyze the performance of submerged hollow fiber systems with different conditions in terms of feed water characteristics and membrane material. A series of experiments with synthetic feed and raw water were carried out using hydrophilic and hydrophobic membrane modules. The model successfully fits the experimental results for synthetic feed as well as raw water. The major fouling mechanisms for filtration of raw water using hydrophilic and hydrophobic membranes are identified as cake formation and standard blocking, respectively. The model calculations indicate that the distributions of flux and cake (fouling) resistance are sensitive to the fiber length of the membrane.

A combined fouling model to describe the influence of the electrostatic environment on the cross-flow microfiltration of BSA

In this paper, the influence of pH in the 3–9 interval and NaCl concentration up to 25 mM on the cross-flow microfiltration of BSA was studied. A tubular ceramic membrane with a mean pore size of 0.14 μm was employed. The evolution of permeate flow and BSA transmission with time was determined at 30 °C, a cross-flow velocity of 3.28 m/s and a transmembrane pressure of 100 kPa. The flow data were discussed by means of combination of two fouling mechanisms: complete and standard blocking when transmission of proteins occurred and complete blocking and cake formations otherwise. The effective radius of the protein and the electrostatic interactions protein–membrane explained the transmission protein values.

Nonuniform deposition of particles inside the pores of a semipermeable membrane

Macroscopic equations of the theory of filtration through granular beds are used to consider the spatial nonuniformity of particle deposition on pore walls during the standard blocking of the pores of ultrafiltration (UF) and microfiltration (MF) membranes. It is shown that the thickness of the layer of particles deposited inside the pore is characterized by a high degree of nonuniformity, which considerably affects the values of membrane permeate flux and selectivity. The effect of pore diameter, pore length, transmembrane pressure, and the coefficient of particle deposition onto the inner pore surface on the performance of standard blocking is studied. A dimensionless number representing the combination of the above parameters is proposed. The number can be used for optimizing the choice of membranes and process parameters for the UF and MF processes using standard blocking.

Activation of the SspA Serine Protease Zymogen of Staphylococcus aureus Proceeds through Unique Variations of a Trypsinogen-like Mechanism and Is Dependent on Both Autocatalytic and Metalloprotease-specific Processing

The serine and cysteine proteases SspA and SspB of Staphylococcus aureus are secreted as inactive zymogens, zSspA and zSspB. Mature SspA is a trypsin-like glutamyl endopeptidase and is required to activate zSspB. Although a metalloprotease Aureolysin (Aur) is in turn thought to contribute to activation of zSspA, a specific role has not been demonstrated. We found that pre-zSspA is processed by signal peptidase at ANA(29) downward arrow, releasing a Leu(30) isoform that is first processed exclusively through autocatalytic intramolecular cleavage within a glutamine-rich propeptide segment, (40)QQTQSSKQQTPKIQ(53). The preferred site is Gln(43) with secondary processing at Gln(47) and Gln(53). This initial processing is necessary for optimal and subsequent Aur-dependent processing at Leu(58) and then Val(69) to release mature SspA. Although processing by Aur is rate-limiting in zSspA activation, the first active molecules of Val(69)SspA promote rapid intermolecular processing of remaining zSspA at Glu(65), producing an N-terminal (66)HANVILP isoform that is inactive until removal of the HAN tripeptide by Aur. Modeling indicated that His(66) of this penultimate isoform blocks the active site by hydrogen bonding to Ser(237) and occlusion of substrate. Binding of glutamate within the active site of zSspA is energetically unfavorable, but glutamine fits into the primary specificity pocket and is predicted to hydrogen bond to Thr(232) proximal to Ser(237), permitting autocatalytic cleavage of the glutamine-rich propeptide segment. These and other observations suggest that zSspA is activated through a trypsinogen-like mechanism where supplementary features of the propeptide must be sequentially processed in the correct order to allow efficient activation.

Selection of membranes for deadend micro- and ultrafiltration outside-in hollow fiber filters

A mathematical model taking into account the adsorption of particles around a membrane pore mouth at the stage of standard blocking is developed. The model is used to study the effect of the average membrane pore size, the cutoff coefficient, and the ratio of the length of the pore inlet region to be blocked to the whole pore length on the product flow rate of a deadend outside-in hollow fiber filter. It is shown that the use of membranes with an average pore size higher than the cutoff diameter for the particles to be removed from the suspension will be profitable only for the first 15–20 min of operation. In this case, the membrane should have an average pore size as large as possible, but not exceeding a limit value at which the membrane selectivity can drop; the cutoff coefficient as low as possible; and a pore inlet region to be blocked as long as possible.

A re-evaluation of gelsolin at ectoplasmic specializations in sertoli cells: The influence of serum in blocking buffers on staining patterns

In this study, we test the hypothesis that gelsolin immunolocalized in actin filament-rich ectoplasmic specializations may be exogenous gelsolin present in normal serum used in blocking buffers, and that binds to the intercellular adhesion plaques during tissue processing. Fixed frozen sections of rat and rabbit testis were pre-treated with standard blocking buffers containing 5% normal goat serum (NGS) and then incubated with anti-gelsolin antibodies in the presence of 1% NGS. Other sections were treated in a similar fashion, but in buffers not containing NGS. Sections were then labeled with secondary antibody conjugated to a fluorochrome. Localized staining at ectoplasmic specializations occurred only in sections treated with NGS. The only positive staining in sections not treated with NGS was associated with seminiferous tubule walls and blood vessels in rabbit tissue. The antibodies reacted with a single band at the appropriate molecular weight for gelsolin on immunoblots of NGS, but did not react on immunoblots of testis or seminiferous epithelium. We conclude that gelsolin localized at ectoplasmic specializations using current commercially available antibodies is a result of non-specific binding to the fixed tissues of gelsolin present in blocking buffers.

Membrane processes for water reuse from the effluent of industrial park wastewater treatment plant: a study on flux and fouling of membrane

Both the relationship between the flux and the fouling mechanism of ultrafiltration (UF) membrane and the effects of pretreatment before reverse osmosis (RO) process on the treatment of the effluent of industrial park wastewater treatment plant (IPWTP) were investigated to examine the application of membrane processes on the water reuse treatment. For the former, the flux data was first fitted to the Hermia model to give the implication of the fouling mechanism. Then, the fouling mechanism was further identified with the aid of the SEM morphology of membrane surfaces. For the latter, the changes of both water characteristics (turbidity, TOC, conductivity, particle size distribution, and organic solute molecular weight) and membrane properties (surface zeta potential and surface morphology) before and after the treatment of membrane processes were measured. It was found that the major blocking mechanisms of UF membrane process at initial and final stage were standard blocking of pore (causing from colloid materials) and cake blocking of pore (causing from suspended particles), respectively. On the other hand, it was concluded that the permeate from 1 μm/UF/RO process was suitable for the reuse of cooling water and low pressure boiler water.

Dynamic optimization of a dead-end filtration trajectory: Blocking filtration laws

An operating model for dead-end membrane filtration is proposed based on the well-known blocking laws. The resulting model contains three parameters representing, the operating strategy, the fouling mechanism and the fouling potential of the feed. The optimal control strategy is determined by minimizing the energy consumption for a fixed final time and produced volume. It was found that constant power filtration leads to minimal energy consumption. Constant flux and constant pressure filtration have equal energy costs. However, compared to strategies with a non-decreasing pressure and non-increasing flux, the relative savings are small. Only if the fouling mechanism resembles standard blocking and the fouling resistance is large compared to the membrane resistance, it may be attractive to implement the optimal trajectory.

THE EFFECT OF AIR BUBBLES FROM DISSOLVED GASES ON THE MEMBRANE FOULING IN THE HOLLOW FIBER SUBMERGED MEMBRANE BIO-REACTOR (SMBR)

There is a possibility of the production of the air bubbles in membrane pores due to the reduction in pressure during membrane filtration. The effect of fine air bubbles from dissolved gases on microfiltration was investigated in the submerged membrane bio-reactor (SMBR). The (air bubble resistance) was defined as the filtration resistance due to the air bubbles formed from the gasification of dissolved gases. From the results of filtration tests using pure water with changes in the dissolved oxygen concentration, the air bubbles from dissolved gases were confirmed to act as a foulant and; thus, increase the filtration resistance. The standard pore blocking and cake filtration models, SPBM and CFM, respectively, were applied to investigate the mechanism of air bubble fouling on a hollow fiber membrane. However, the application of the SPBM and CFM were limited in explaining the mechanism due to the properties of air bubble. With a simple comparison of the different filtration resistances, the portion was below 1% of the total filtration resistance during sludge filtration. Therefore, the air bubbles from dissolved gases would only be a minor foulant in the SMBR. However, under the conditions of a high gasification rate from dissolved gases, the effect of air bubble fouling should be considered in microfiltration.

Removal of CrO 4 anions from waters using surfactant enhanced hybrid PAC/MF process

The removal of CrO 4 2− anions from aqueous solution using surfactant added hybrid powdered activated carbon (PAC) and crossflow microfiltration (CFMF) process was performed. Experimental runs were studied at various amounts of cetyl trimethyl ammonium bromide (CTAB) as cationic surfactant, PAC as adsorbent and CrO 4 2− ions in feed solution. CFMF unit was operated at constant values of the transmembrane pressure (150 kPa), crossflow velocity (1.18 m/s) and temperature (30 °C). Hybrid PAC/MF process performance was investigated in terms of CTAB and CrO 4 2− rejections and, the flux decline. It was shown that the flux declined with time and the rejections varied for various properties of feed solution. CTAB and CrO 4 2− rejections could be achieved as 91 and 97.2% at the conditions of 0.5 g PAC/L, 5 mM CTAB, 0.2 mM CrO 4 2− and 120-min process time. It was found that over the critic micelle concentration (CMC), both CTAB and CrO 4 2− rejections were in the higher values according to the values under the CMC. In addition, membrane blocking mechanisms were investigated to clarify the cake formation mechanism due to PAC. For all experimental conditions, the best results of blocking models obtained for cake filtration, intermediate blocking and standard pore blocking, respectively. It was understood that these blocking mechanisms occurred simultaneously on membrane surface in terms of high r 2 values. A cake layer formed on membrane surface (cake filtration). Pore entrance blocked partially due to particles bridging over pore opening (intermediate blocking). Free CTAB aggregates with or without CrO 4 2− anions, entered into the membrane pores, caused to a layer formation by adsorption and entrapment on the membrane's pore walls (standard pore blocking). Besides, cake resistance ( R c), specific cake resistance ( α), modified fouling index (MFI) and total dried solid mass of cake per unit membrane area ( ω) were also determined to comprehend the reasons of clogging within the membrane and on the surface due to both CTAB aggregates and PAC, respectively. Membrane fouling (MFI) increased with the increasing of PAC, CTAB and CrO 4 2− amounts in feed solution. As a result, flux, rejections and fouling in membrane were shown as a dynamic function of PAC, CTAB and CrO 4 2− as the properties of the feed solution.

Fouling mechanisms of alginate solutions as model extracellular polymeric substances

Extracellular polymeric substances (EPS) are viewed as major fouling components during filtration of biological feeds in industry. However, very few studies investigated the fouling mechanisms of polysaccharides, one major group of macromolecules in EPS. In this work, dead end unstirred filtration of sodium alginate, a model polysaccharide, was carried out and analysed using classic filtration laws and the combined pore blockage and cake formation model. It was found that the cake model appears to fit the entire range of the ultrafiltration data while the consecutive standard pore blocking model and cake model are more applicable to microfiltration membranes (0.2 m track-etched and 0.22 m PVDF membranes). The specific cake resistance (α c ) (approximately 1×10 16 m/kg) is similar to α c of bovine serum albumin (BSA) and actual EPS in MBR systems reported in the literature, and higher than that of many colloidal particles. α c increases with the increase of alginate concentration but slightly decreases with the presence of BSA in the feed solution. The alginate cake obtained during filtration features both low compressibility and low porosity despite some differences between different membranes. The lack of a full flux recovery following filtration interruption implies the existence of strong intermolecular attractive interactions within the alginate fouling layer.

Membrane filtration of leather plant effluent: Flux decline mechanism

The flux decline mechanisms involved during nanofiltation (NF) of the pretreated leather plant effluent (collected from all the beam house processing units, except chrome tanning) are analyzed. The same analysis is carried out for reverse osmosis (RO) of permeate of NF. The flux decline during NF is explained by three consecutive mechanisms, namely, complete pore blocking, standard pore blocking and cake filtration. The flux decline for RO is explained by above mentioned two pore blocking steps. For NF, blocking coefficients are found to be increasing functions of the operating pressure; whereas, for RO, the trends are found to be reverse. The cake formation during NF is analyzed and the specific cake resistances at various operating pressures are evaluated. A simple and standard resistance-in-series model is proposed to quantify the flux decline and estimation of the various resistances.

Genotyping the Butyrylcholinesterase in Patients with Prolonged Neuromuscular Block after Succinylcholine

Succinylcholine remains the standard neuromuscular blocking drug for tracheal intubation in emergency situations. The short duration of action is due to its rapid hydrolytic degradation by butyrylcholinesterase (plasmacholinesterase). Multiple variants of this enzyme are known (A, F, S, H, J, K variants) with different effects on enzyme activity. This study was undertaken to evaluate the use of molecular genetic methods in patients with clinically prolonged neuromuscular block. Nine patients with a neuromuscular block of 14 min to 5 h were selected. All four exons of the butyrylcholinesterase were amplified by polymerase chain reaction and analyzed by automated sequencing. Molecular genetic results were compared with clinical relaxation time and with biochemical test results (total butyrylcholinesterase activity, dibucaine and fluoride inhibition). Seven of nine patients were mutation carriers. Five of these had more than one mutation. The A and K variants were the most frequent variations. Three of four patients who were homozygous for the A variant were also carriers of the K allele. The authors identified one novel mutation (G1294T) introducing a stop codon at amino acid position 432. The duration of neuromuscular block was substantially different between patients with identical butyrylcholinesterase genotypes. Variations in the genetic sequence of butyrylcholinesterase are frequent in patients with prolonged duration of action of succinylcholine. Direct sequencing of the whole butyrylcholinesterase gene is an appropriate method for genotyping and, accordingly, should be used in future clinical studies with drugs metabolized by this enzyme (e.g., succinylcholine, mivacurium).