Microfiltration Layer Research Articles

Development and characterization of an asymmetrical flat microfiltration membrane based on natural phengite clay: Application as a pretreatment for raw seawater reverse osmosis desalination

The work focuses on developing a new asymmetric flat microfiltration membrane using an inexpensive geological material, natural Moroccan phengite clay. The optimal porous ceramic support was prepared by applying the paste casting method and sintering at a low temperature of 1050 °C for 2 h. Secondly, the microfiltration layer was developed by the spin coating method. The layer was then dried and sintered at 850 °C/2h. SEM analysis revealed that the morphological structure of the layer is homogeneous and free from cracks. Furthermore, the microfiltration layer has an average pore size of 1.23 μm, a thickness ranging from 30.3 μm to 31.3 μm, a water permeability of 258.1 L/h.m2.bar, and good chemical stability against corrosion. The performance of the manufactured membrane was evaluated by filtering raw seawater (RSW1 and RSW2) as a potential application for seawater pretreatment before desalination by reverse osmosis. The prepared membrane significantly reduced turbidity concentrations by 98.7 % for RSW1 and 96.8 % for RSW2. The fouling and antifouling mechanisms were also examined. Finally, the preparation cost of the phengite membrane was estimated to be 125 $/m2.

Composite GO/Ceramic Membranes Prepared via Chemical Attachment: Characterisation and Gas Permeance Properties.

Graphene oxide (GO) oligo-layered laminates were self-assembled on porous ceramic substrates via their simple dip-coating into aqueous GO dispersions. To augment the stability of the developed composite GO/ceramic membranes and control the morphology and stacking quality of the formed laminate, short-((3-glycidoxypropyl)trimethoxy silane-GLYMO, (3-aminopropyl)triethoxy silane-APTES), and long-chain (polydopamine-PDA) molecules were involved and examined as interfacial linkers. A comparative study was performed regarding the linker's capacity to enhance the interfacial adhesion between the ceramic surface and the GO deposit and affect the orientation and assemblage characteristics of the adjacent GO nanosheets that composed the formed oligo-layered laminates. Subsequently, by post-filtrating a GO/H2O suspension through the oligo-layered laminate membranes, the respective multi-layered ones have been developed, whereas ethylenediamine (EDA) was used in the suspension as an efficient molecular linker that strongly bonds and interlocks the GO nanosheets. The definition of the best linker and approach was conducted on macroporous α-alumina disks, due to the use of inexpensive raw materials and the ability to fabricate them in the lab with high reproducibility. To validate the concept at a larger scale, while investigating the effect of the porous substrate as regards its micrometer-scale roughness and surface chemistry, specific chemical modifications that yielded membranes with the best gas permeability/selectivity performance were replicated on a commercial single-channel monolith with a ZrO2 microfiltration layer. XRD, Raman, ATR, FESEM, and XPS analyses were conducted to study the structural, physicochemical, surface, and morphological properties of the GO/ceramic composite membranes, whereas permeance results of several gases at various temperatures and trans-membrane pressures were interpreted to shed light on the pore structural features. Concerning the short-chain linkers, the obtained results ascertain that GLYMO causes denser and more uniform assembly of GO nanosheets within the oligo-layered laminate. PDA had the same beneficial effect, as it is a macromolecule. Overall, this study shows that the development of gas-separating membranes, by just dipping the linker-modified substrate into the GO suspension, is not straightforward. The application of post-filtration contributed significantly to this target and the quality of the superficially deposited, thick GO laminate depended on this of the chemically attached oligo-layered one.

One-step sintering for anti-fouling piezoelectric α-quartz and thin layer of alumina membrane

Lead-free piezoelectric ceramics are attracting significant attention in the construction of separation membranes because they offer a self-cleaning function and have no risk of lead leaching from the materials. In this study, the fabrication of cost-sensitive and self-cleaning ceramic composite membranes via co-sintering of a porous α-quartz green support and an alumina microfiltration layer is reported. The α-quartz green support prepared by aqueous gel-casting has benign wettability and flexural strength, which is beneficial for forming a thinner and homogeneous membrane layer by dip-coating. The effects of the co-sintering temperature and dip-coating parameters on the pore size, permeance, mechanical and chemical stabilities, and piezoelectric properties were further investigated. The optimal membrane had an average pore size of 190 nm by co-sintering at 1200 °C and a strongest ultrasound response of 15 mV at an alternating voltage (AV) of 100 V. Finite element analysis showed that the composite membrane generated a beneficial displacement and acoustic pressure (acpr) for cavitation effect. In-situ mitigation of fouling was demonstrated during 500 ppm oil-in-water (O/W) emulsion filtration, which resulted in a stationary flux (Jstat) of 190 L m−2 h−1·bar−1, increased by 65.7% at 100 V AV.

New low-cost tubular ceramic microfiltration membrane based on natural sand for tangential urban wastewater treatment

In wastewater treatment, the development of low-cost separation methods is of significant importance. Low-cost membranes based on natural materials have become a highly active research topic in recent years. Herein, using low-cost natural Moroccan sand, new ceramic supports have been developed and characterized using different techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), along with scanning electron microscope (SEM). Plastic paste (average particle size ≤125 µm) was blended with organic additives and water, then the obtained paste was extruded into porous tubular supports. The support had a porosity of 43%, water permeability of 1928 L/h m2 bar, excellent chemical and mechanical properties and an average pore diameter in the range of 8–15 µm after firing at 950 °C/2 h. As per SEM analysis, the tubular supports had a smooth and crack-free surface. The slip casting process was used to create a microfiltration layer from the same natural sand powder (average particle size ≤63 µm) using a mixture of powder sand, water, and polyvinyl alcohol solution. The water permeability of the microfiltration membrane sintered at 950 °C/2 h was 1052 L/h m2 bar, the average pore size diameter was about 0.90 µm and 82% of pores had a diameter ≤1.00 µm. The obtained microfiltration membrane was tested for the treatment of urban wastewater. The membrane showed excellent separation performance in turbidity removal and chemical oxygen demand.

Application of the Experimental Design for the Optimization of Microfiltration Membrane

In the present study, the effect of zirconia powder content, polyvinyl alcohol (PVA), Contact time and sintering temperature of zirconia microfiltration membrane elaboration were evaluated using Plackett-Burman design (PBD) and investigated by thickness and pore diameter. The zirconia microfiltration membrane has been prepared by the powder suspension technique. A deflocculated suspension of zirconia was obtained by mixing (5-10% w/w) of zirconia, (30-35% w/w) of PVA (12% w/w aqueous solution) as binder and water. The zirconia layer was deposited on the inner surface of clay support by slip casting with a contact time (2-5 min). After drying at room temperature, the ZrO2 membrane was sintered (800-1000°C) for 2 hours. By using PBD, sintering temperature, PVA and zirconia were recognized and selected as important effectives parameters of pore diameter; On the other hand, PVA and contact time were the main controlling parameters of the thickness of zirconia microfiltration layer. The optimal factors to elaborate the microfiltration membrane by using experimental design include a sintering temperature of 1000°C, zirconia content of 5%, PVA content of 30% and contact time of 2 min predicting a pores diameter of 0,24 µm and thickness of 24 µm.

Self-cleaning performance of in-situ ultrasound generated by quartz-based piezoelectric membrane

• A self-cleaning membrane coupled with in-situ ultrasound function was developed. • The membrane is composed of an anti-fouling layer and a piezoelectric support. • The internal ultrasound induced shear force to slow down the particle settling. • Foulants can be removed by in-situ ultrasound at relatively low power intensity. Membrane separation technology is playing a prominent role in treatment of suspension wastewater, but its efficiency is limited by membrane fouling. Here, a self-cleaning piezoelectric ceramic membrane (PCM) coupled with in-situ ultrasound functionality was developed. The PCM consists of a porous piezoelectric quartz (ɑ-SiO 2 ) support and a ZrO 2 microfiltration (MF) layer. The MF layer serves as a separation membrane, and it possesses a smooth and negatively charged surface, which is beneficial to weaken the interaction between membrane and foulants. The ɑ-SiO 2 support provides mechanical strength to the membrane and can generate internal ultrasound to mitigate fouling. In MF process, particulate foulants are inevitably deposited on the membrane surface, forming a cake whose permeance resistance is 3.9 times of pristine membrane. With the assistance of internal ultrasound, the thickness of cake decreased from 64.2 to 48.4 μm, and porosity increased from 39.5% to 42.5% due to the formation of shear force. Higher cross-flow velocity and more vigorous ultrasound intensity are helpful to strengthen turbulence, which can improve stationary membrane flux by 41.7%. The fouling removal efficiency of internal ultrasound is superior to the outer one, and the economic evaluation indicates that the cost of water production can be saved in the presence of ultrasound.

α‐Amylase Immobilization on Ceramic Membranes for Starch Hydrolysis

Abstractα‐Amylase has many applications in various fields, especially in the food industry where it is used in starch hydrolysate production. However, the use of free enzymes is disadvantageous as the enzymes cannot be recovered from the reaction medium and are therefore used only once. The challenge of the biological pollution of wastewater can be tackled using immobilized enzymes as they possess higher stability as well as the possibility of repeated and continuous use. In this paper, adsorption and covalent methods of α‐amylase immobilization on ceramic membranes are developed and their advantages and disadvantages are identified. For these purposes, silica ceramic membranes with a microfiltration layer (pore sizes 1–5 µm) are first used. The dependences of immobilized α‐amylase activity on enzyme concentration and reaction time are determined and compared with the free enzyme. The influence of pH, temperature, and reusability on adsorbed enzyme activity is investigated. Thus, a novel combination of filtration and biocatalytic functions on one membrane is introduced. The results obtained are crucial for controlling certain characteristics of hydrolysis during industrial processes.

Characterization and antifouling property of synthesized graphene oxide nanoparticles

Graphene oxide was made from graphite by Hummer’s method.This method is economical and easily controlled and a best approach for extensive production of GO. Fabrication of a nanofiltration membrane was done from a microfiltration membrane. The formation of grapheme oxide was confirmed by SEM, FTIR spectroscopy and XRD. SEM investigation indicated that graphene oxide fills the pores of microfiltration layer. The subsequent structure was portrayed by (XRD). FTIR shows the nearness of oxygen-containing down to earth groups. SA and HA antifouling operators were used to test the antifouling property of the film. The FRR values of GO nanoparticles are 84% for SA and 90% for HA.

Surface treatments and functionalization of metal‐ceramic membranes for improved enzyme immobilization performance

AbstractBACKGROUNDEnzyme immobilization in porous membranes often improves enzyme performance. This work reports the preparation and characterization of robust and scalable asymmetric metal‐ceramic microfiltration membrane. The surface of the porous metal‐ceramic membrane was treated by impregnation with a ceramic oxide for enzyme adsorption and corrosion protection. Finally, enzyme immobilization in the support was investigated.RESULTSThe bilayer membrane was successfully fabricated by combining a ceramic microfiltration layer with a metal support by tape casting, lamination and co‐sintering. A pore size in the ceramic microfiltration layer of 0.4 μm resulted in high water permeability (12 000 L/(m2 h bar)). Two different surface treatments were compared: heat treatment and yttrium(III) oxide (Y2O3) impregnation. Corrosion stability tests under enzyme‐relevant conditions gave no detectable chemical or structural changes. Alcohol dehydrogenase (EC 1.1.1.1) was immobilized in the membrane by physical adsorption and by two covalent immobilization methods. Covalent immobilization significantly improved enzyme loading, activity, and recyclability. Membrane reuse by heat treatment removed fouling, but decreased immobilization performance.CONCLUSIONThe improved microstructure obtained by Y2O3‐impregnation had a significant effect on enzyme loading yield and activity. This indicates the potential of this surface modification method and of these metal‐supported ceramic membranes in enzyme immobilization. Covalent immobilization was superior. © 2019 Society of Chemical Industry

Asymmetric mullite membranes manufactured by phase-inversion tape casting from polymethylsiloxane and aluminum diacetate

Polymethylsiloxane (MK) and aluminum diacetate have been stoichiometrically combined to synthesize a mullite-based powder (3Al2O3·2SiO2) at 850 °C (5 h) or 1200 °C (3 h). High-purity crystalline mullite (>99%) was obtained by heating the mixture in the air (thermal oxidation) at 1200 °C for 3 h, mainly due to the formation of highly reactive silica and alumina precursors. Afterward, the mullite-based powders were used to prepare planar asymmetric microfiltration membranes by phase-inversion tape casting. The green membranes were sintered at 1600, 1650 or 1700 °C during 2 h. The asymmetric morphology identified in the membranes by scanning electron microscopy analysis reveals a thin skin-layer (microfiltration layer, <10 μm) followed by a porous support, in which two different structures were observed: finger- and/or sponge-like layer. Water permeation performance in a dead-end configuration was investigated at different pressures (3, 4, and 5 bar). The obtained results clearly indicated an improved water permeation flux compared to a symmetric commercial membrane (133.6 m³/m2·h compared to 14.7 m³/m2·h, respectively, at 5 bar). This observation could be ascribed to the asymmetric morphology resultant from the phase-inversion process.

One step co-sintering process for low-cost fly ash based ceramic microfiltration membrane in oil-in-water emulsion treatment

Ceramic membranes with higher chemical stabilities and organic solvent resistances are indispensable for water purification. The fabrication of low-cost ceramic membranes (lower sintering consumption and cheaper membrane materials) facilitates practical water treatment applications. In this study, a novel process for the fabrication of a low-cost fly ash based microfiltration (MF) membrane via a co-sintering process was proposed. In the novel process, the MF layer was sprayed on a “green” fly ash support and co-sintered. The mullite fibers with excellent heat resistance and stability were proposed to alleviate the shrinkage difference in the co-sintering process, and improve the porosity and bending strength of the support. The raw material cost, energy consumption, and preparation period of the ceramic membrane could be significantly reduced. The prepared ceramic MF membrane had an average pore size of 100 nm with a high permeability of 450 Lm−2 h−1 bar−1. Moreover, it exhibited a high total organic carbon (TOC) removal efficiency (>99%) for oil-in-water (O/W) emulsion, and a high stable permeability of 165 Lm−2 h−1 bar−1 was maintained. This technique, combining low-cost materials and the co-sintering process, can serve as a cost-effective method for the production of high-performance ceramic membranes for water purification.

New Tubular Ceramic Membranes from Natural Moroccan Clay for Microfiltration Application

This paper is devoted the preparation of low cost microfiltration membranes using Moroccan clay powder. The preparation of membrane was composed with two steps: First a macroporous tubular support with a pore diameter 10 μm and porosity 43%. Secondly a microfiltration layer was performed by the slip casting method. A deflocculated slip was obtained by mixing mineral powder of ZrO2, PVA (polyvinyl alcohol) and water, after drying at room temperature for 24 h, the microfiltration layer was heated to 800°C for consolidation. Scanning electron microscopy observation showed homogeneous layers without cracks with an average pore diameter of 0.19 μm for the active layer. Water permeability obtained is about 841 L/h.m2.bar. The membranes have been tested to cleaning of colored wastewater.

One-step preparation of high-performance bilayer α-alumina ultrafiltration membranes via co-sintering process

Compared to the traditional separation technology, membrane separation is particular beneficial for the treatment of contaminated fresh water such as agricultural runoff, and hydraulic fracturing wastewater. However, the development of cost-effective membranes with both high permeability and high rejection performance is still a challenge. In this study, we design one-step preparation of high-performance bi-layer α-alumina ultrafiltration (UF) membranes supported on coarse tubular substrates via co-sintering process. In this approach, boehmite sol and alumina nanoparticles were mixed in different ratios for the fabrication of microfiltration (MF) layer and UF layer, respectively. The effects of dip-coating dispersion formulation, coating time and thermal treatment process on the membrane microstructure and performance were comprehensively investigated. It was found that the presence of boehmite sol in the MF layer could accelerate its sintering process, while the addition of alumina nanoparticles into UF layer could promote the phase transition from γ phase to α phase at low temperature and retard the shrinkage. The optimized doping content of boehmite and alumina nanoparticles were 2wt% and 4wt% to achieve a good match of thermal expansion properties between the two co-sintering layers. For MF layer and UF layer, the membrane thickness were controlled to be 40–50µm and about 1µm, respectively. After co-sintering at 1000°C for 2h with a heating rate and cooling rate of 0.5°C/min, tubular α-alumina UF membranes were found to display a high pure water permeability of 70Lm-2h-1bar-1 and a small pore size of ~5nm, which also exhibited good dye removal capabilities in the process of treating dye waste water.

Development and characterization of tubular composite ceramic membranes using natural alumino-silicates for microfiltration applications

The preparation and characterization of porous tubular ceramic composite microfiltration membranes, using kaolins and calcium carbonates, were reported. The porous gehlenite (2CaO·Al2O3·SiO2) and anorthite (CaO·Al2O3·2SiO2) based ceramics were obtained by a solid state reaction. A ceramic support, sintered at 1250°C, within an average pore size of about 8μm, a porosity of about 47% and a compression strength around 40MPa, was prepared. The microfiltration active top layer was added on the support by a slip casting from clay powder suspensions. The novel microfiltration membrane layer has a thickness of 40μm and an APS value of about 0.2μm. This average pore size value was improved and considerably lower than those reported in the literature (0.5μm). The performance of the novel microfiltration ceramic membrane was determined for evaluating both the water permeability and rejection. This proved the potentiality of the membrane produced in the microfiltration field. Moreover, the good adhesion, between the support and the active microfiltration layer membranes, was also proved. A correlation between microstructures of used powders and physicochemical properties was discussed. Finally, the origin of the unique two powder order membrane depositions was also proposed.

New ceramic membranes from natural Moroccan phosphate for microfiltration application

This paper is devoted to preparation of low-cost microfiltration (MF) membranes using lixiviated phosphate powder crushed at 50 μm. The filtering layer was coated on phosphate tubular support with 10μm pore diameter and 43% porosity. The preparation of this ceramic layer was performed by the slip-casting method. A deflocculated slip was obtained by mixing mineral powder, polyvinyl alcohol, and water with dispersant. After drying at room temperature for 24 h, the MF layer was heated to 800°C for consolidation. Scanning electron microscopy observation showed homogeneous layers without cracks with an average pore diameter of 0.35μm for the active layer, the thickness is approximately 10 μm. Water permeability obtained is about 700 L/h m2 bar. The membranes have been tested to treat wastewater of phosphate industry, to clarify synthetic solutions of lime and aluminum hydroxide, and to remove bacteriological pollution present in water wells. The experiments carried out show that elaborated MF membrane is very efficient for the reduction of turbidity, total phosphorus, and number of bacterial germs with almost the same performances than that obtained with a commercial α-alumina membrane.

Elaboration of new tubular ceramic membrane from local Moroccan Perlite for microfiltration process. Application to treatment of industrial wastewaters

In this study, an original microfiltration tubular membrane (M1) made from local Moroccan Perlite was used to treat three wastewater types: effluents coming from beamhouse section of tannery (effluent A), textile effluent coming from jeans washing process (effluent B), and dicing wafer effluent generated by electronic industries (effluent C). The prepared membrane is composed of two layers of Perlite with two different granulometries: a macroporous support with a pore diameter centered near 6.6μm and porosity of about 42%, and a microfiltration layer, performed by slip casting method, with a mean pore size of 0.27μm. The water permeability determined of the membrane is 815L/hm2bar. Tangential microfiltration using Perlite membrane proved to be effective in removing pollutants from the three effluents with almost the same efficiencies than that obtained with a commercial Alumina membrane (M2) with a pore diameter of 0.2μm and a water permeability of 1022L/hm2bar. Tangential microfiltration process operated at lower pressure (1bar) was seen to remove turbidity from the three feeds completely. Perlite membrane allowed significant reduction of Chemical Oxygen Demand COD (50–54%) and Total Kjeldahl Nitrogen TKN (56%) of beamhouse effluent. It showed a significant decrease of COD (54–57%) and a complete discoloration of textile wastewater.

Grafting of fluoroalkylsilanes on microfiltration Tunisian clay membrane

Ceramic membranes can be described by an asymmetric porous material formed by a macroporous support with successive thin layers deposited on it. Paste from Tunisian silty marls referred M11, is extruded to elaborate a porous tubular configuration used as supports. The support heated at 1190 °C, shows an average pore diameter and porosity of about 9.20 μm and 49%, respectively. The elaboration of the microfiltration layer based on Tunisian clay referred JM18, is performed by slip-casting method. The heating treatment at 900 °C leads to an average pore size of 0.18 μm. The obtained membrane was surface modified to change their hydrophilic character into hydrophobic one by the grafting of the triethoxy-1H,1H,2H,2H-perfluorodecylsilane C 8F 17(CH 2) 2Si(OC 2H 5) 3. The resulting products were investigated using Fourier transform infrared spectroscopy FTIR and thermogravimetric analysis TGA. The new surfaces were examined by water contact-angle measurements, Scanning Electron Microscopy (SEM) and the water fluxes through the grafted membranes were also measured. Results of the grafting of microfiltration membrane with fluoroalkylsilane will be given and discussed. The new hydrophobic membrane seems to be promising in the field of membrane distillation. High salt rejection rates higher than 99% were obtained for modified MF ceramic clay membrane.

Synthesis and characterization of a new inorganic ultrafiltration membrane composed entirely of Tunisian natural illite clay

New ceramic multilayer membranes with a top layer of Tunisian natural illite clay were prepared. The illite powder (fine fraction less than 2 µm in size) was isolated by sedimentation from crude clay. The obtained powders of a specific surface area of 160 m 2g –1 were analyzed by X-ray diffraction (XRD). It was found that the principal material of this sample was illite. The deposition of the ultrafiltration layer occurred by slip casting method on aclay microfiltration layer using aqueous colloidal suspension. After drying at room temperature for 24 h, the ultrafiltration layer was heated to 800°C. SEM analyses showed that very thin defect-free top layers were formed. The layer thickness increased with dipping time but could be limited to a few micrometer (4.82 µm). The membrane was further tested for ultrafiltration of dextran polymer solution of different molecular weights. The membrane cut-off was of 185 KDa and the water permeability was equal to 88 l.h –1m –2 bar –1.

Study of performances of ceramic microfiltration membrane from Tunisian clay applied to cuttlefish effluents treatment

Microfiltration membrane is increasingly used in wastewater treatment to produce a higer quality effluent. In this study a microfiltration membrane from Tunisian clay (JM 18/SI 2) was used to treat cuttlefish effluents generated from the conditioning (freezing and washing) seawater food industry which consume a great amount of water. In Sfax (Tunisia), about 1000 m 3/day are usually discharged in the littoral. The prepared membrane is composed of two layers: a support (SI 2) with a pore diameters centred near 6.3 μm and porosity of about 48.5%, and a microfiltration layer (JM 18) with a mean pore size of 0.18 μm. Cross-flow microfiltration was carried out then, in order to reduce the pollutants content expressed in term of turbidity and dissolved organic carbon (DOC). Both industrial ceramic membrane from α-alumina and elaborated membrane from Tunisian clay were used for this study. The results reveal that the values of DOC retention rate and turbidity are nearly the same: about 65% and 1 NTU respectively. So, it seems that the prepared microfiltration membrane is suitable for this kind of waste water treatment.

Synthesis of aluminium hydrates by a precipitation method and their use in coatings for ceramic membranes

Aluminum hydrates were synthesized using AlCl3·6H2O as the starting material by the precipitation method. The phases of the obtained powder were amorphous, boehmite, bayerite and nordtsrandite depending on the pH of the solutions. The weight loss of the powders by dehydration was increased with the lowering pH condition of solution. Aluminum hydrates transformed to α-Al2O3 via γ-Al2O3, δ-Al2O3 and θ-Al2O3, and particle sizes were grown by increment of the heating temperature. The crystallite size and specific surface area were rapidly changed over 1100°C which is the formation temperature of the α-Al2O3 phase. The γ-Al2O3 powder was coated on an intermediate layer of ceramic membrane by the slip casting method, and an unsupported membrane was also prepared for comparison. The supported microfiltration layer showed a porous structure with small grains, but the unsupported layer revealed interconnected larger grains. Grain growth was more dominant in the unsupported layer than in the supported one due to interaction between the support and the supported layer. An ultrafiltration membrane with homogeneous microstructure was formed using boehmite particulate sol, and abnormal grain growth in unsupported membrane was also observed similar to microfiltration layer.