Hollow Fiber Microfiltration Membranes Research Articles

Emerging contaminants removal through fluorine-doped carbon hollow fiber microfiltration membrane based on metal-free electro-Fenton

The emerging contaminants with high toxicity and bioaccumulation potentially threaten to human health, which was difficult removed by traditional biological treatment or membrane separation. In view of this, a novel type of fluorine (F)-doped carbon hollow fiber microfiltration membrane was prepared for realizing emerging contaminants removal through metal-free electro-Fenton. Herein, polyaniline (PANI) was used as a precursor for preparation of porous carbon membrane. The graphitic N and pyridinic N on porous carbon were used as the active sites for H2O2 production and its further activation to ·OH, which realized metal-free electro-Fenton reaction. According to the results, the carbon nanotubes with F-PANI at the ratio of 1:1 and calcination temperature at 300°C endowed the membrane moderate resistance and pure water permeability of 430 Ω and 48.51 L/(m2·h·bar), respectively. Importantly, the intensity of ·OH generation was further significant enhanced by introducing C-F bonding into the membrane. Therefore, the bisphenol A (BPA), sulfamethoxazole (SMZ) and atrazine (ATZ) removal rates were 92.63%, 38.47% and 27.05%, respectively. For control group without bias, the removal rates of above contaminants were 0% removal rates. Moreover, the membrane permeate loss by filtrating BPA, SMZ and ATZ were 0.13, 0.15 and 0.05, which were 0.20, 0.24 and 0.21 for control group.

Preparation of high-flux polyethylene hollow fiber microfiltration membranes with multiple pore structure through the combination technology of braided tube reinforcement and TIPS method

Our team proposed the continuous preparation of the reinforced polyethylene (PE) hollow fiber microfiltration (MF) membranes based on the combination technology of braided tube reinforcement and thermally induced phase separation (TIPS) method. In this work, to improve the permeability and reduce the flux attenuation, we selected PE as the membrane-forming polymer, polyethylene glycol (PEG) and sodium chloride (NaCl) as the composite pore-forming agents to optimize the membrane-forming composition. In particular, the effect of NaCl contents on the permeation of the reinforced PE hollow fiber membranes was studied in detail. The reinforced PE hollow fiber MF membranes obtained the multiple pore structure containing small pores, large pores and cavity structure. The small pores were formed by PEG and white oil. The large pores and the cavity structure were formed by the discreted and agglomerated NaCl, respectively. The cavity structure provided the connectivity gaps for the small pores and forming an internal highly connected pathways, which could reduce the transmembrane resistance. Thus, the flux improved obviously with the increasing NaCl contents. When the NaCl content was 30 wt%, the pure water flux of the reinforced PE hollow fiber MF membranes could reach 1606.0 L·m−2 h−1 after pre-pressuring for 30 min. In addition, the reinforced PE hollow fiber MF membranes exhibited excellent tensile strength with 170.0 MPa and good corrosion resistance, which showed a great application potential in harsh environments. In particular, this method provides a new idea for the continuous preparation of the reinforced PE hollow fiber MF membranes.

Alternating flow direction improves chemical cleaning efficiency in hollow fibre membranes following skim milk microfiltration

With efficient membrane cleaning remaining a challenge, novel approaches have promising potential to enhance cleaning efficiency. This study examined the concept of feed side cyclical and permanent flow reversal during membrane cleaning, to which so far it has not been applied to. Experiments were conducted in a hollow fibre microfiltration membrane with lengths of 0.5 m and 1.0 m using skim milk for deposit formation, NaOH as a cleaning agent, and flux recovery ratio and protein removal for cleaning evaluation. Overall, flow reversal was found to significantly increase cleaning success. Due to the length-dependent pressure drop and flow reversal, the local transmembrane pressure at the initial feed inlet ΔpTM, inlet and thus the ratio of flow velocity to ΔpTM, inlet was increased compared to steady forward flow cleaning. This proved beneficial as it combines high shear stress with low ΔpTM, inlet where fouling was most pronounced after filtration.

Wet dispersion of graphene assisted constructing multiple interface pores of PVDF hollow fiber membranes via melt-spinning and stretching

In this work, in order to further improve the permeability of poly(vinylidene fluoride) (PVDF) hollow fiber microfiltration membranes through melt-spinning and stretching (MS-S), we doped graphene (GE) in the forming membrane system of the previous work via wet dispersion and successfully prepared PVDF hollow fiber microfiltration membranes with multiple interface pores. GE could be uniformly dispersed and embedded in the PVDF matrix through the wet dispersion, which could obviously improve the interface layer between the matrix phase (PVDF) and the dispersed phase (GE) due to their poor compatibility of organic/inorganic phases. In addition, the stress concentration would be generated at the interface between GE and PVDF, which resulted in PVDF forking to many tiny fibers. Thus, the multiple interface pores between organic/organic (PVDF/polysulfone(PSf)) and organic/inorganic (PVDF/GE) phases could occur and be controlled precisely through the further stretching. The results showed that GE could improve the pore size and porosity of the prepared membranes obviously. In addition, the pore size of the prepared membranes could be controlled from 0.258 to 1.066 µm by changing the stretching ratios. Accordingly, pure water flux increased from 174.5 to 2782.9 L m-2 h-1. Applied to filter the active sludge suspension, the prepared PVDF microfiltration membranes exhibited a high rejection (＞99.5%), and the turbidity decreased obviously (˂0.5 NTU). In particular, there were not any hazardous solvents used in the preparation process, which could achieve green preparation of PVDF membranes.

Preparation of Chemically Resistant Cellulose Benzoate Hollow Fiber Membrane via Thermally Induced Phase Separation Method.

For the first time, we have successfully fabricated microfiltration (MF) hollow fiber membranes by the thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS) methods using cellulose acetate benzoate (CBzOH), which is a cellulose derivative with considerable chemical resistance. To obtain an appropriate CBzOH TIPS membrane, a comprehensive solvent screening was performed to choose the appropriate solvent to obtain a membrane with a porous structure. In parallel, the CBzOH membrane was prepared by the NIPS method to compare and evaluate the effect of membrane structure using the same polymer material. Prepared CBzOH membrane by TIPS method showed high porosity, pore size around 100 nm or larger and high pure water permeability (PWP) with slightly low rection performance compared to that by NIPS. On the contrary, CBzOH membranes prepared with the NIPS method showed three times lower PWP with higher rejection. The chemical resistance of the prepared CBzOH membranes was compared with that of cellulose triacetate (CTA) hollow fiber membrane, which is a typical cellulose derivative as a control membrane, using a 2000 ppm sodium hypochlorite (NaClO) solution. CBzOH membranes prepared with TIPS and NIPS methods showed considerable resistance against the NaClO solution regardless of the membrane structure, porosity and pore size. On the other hand, when the CTA membrane, as the control membrane, was subjected to the NaClO solution, membrane mechanical strength sharply decreased over the exposure time to NaClO. It is interesting that although the CBzOH TIPS membrane showed three times higher pure water permeability than other membranes with slightly lower rejection and considerably higher NaClO resistance, the mechanical strength of this membrane is more than two times higher than other membranes. While CBzOH samples showed no change in chemical structure and contact angle, CTA showed considerable change in chemical structure and a sharp decrease in contact angle after treatment with NaClO. Thus, CBzOH TIPS hollow fiber membrane is noticeably interesting considering membrane performance in terms of filtration performance, mechanical strength and chemical resistance on the cost of slightly losing rejection performance.

Preparation of Microfiltration Hollow Fiber Membranes from Cellulose Triacetate by Thermally Induced Phase Separation.

For the first time, self-standing microfiltration (MF) hollow fiber membranes were prepared from cellulose triacetate (CTA) via the thermally induced phase separation (TIPS) method. The resultant membranes were compared with counterparts prepared from cellulose diacetate (CDA) and cellulose acetate propionate (CAP). Extensive solvent screening by considering the Hansen solubility parameters of the polymer and solvent, the polymer’s solubility at high temperature, solidification of the polymer solution at low temperature, viscosity, and processability of the polymeric solution, is the most challenging issue for cellulose membrane preparation. Different phase separation mechanisms were identified for CTA, CDA, and CAP polymer solutions prepared using the screened solvents for membrane preparation. CTA solutions in binary organic solvents possessed the appropriate properties for membrane preparation via liquid–liquid phase separation, followed by a solid–liquid phase separation (polymer crystallization) mechanism. For the prepared CTA hollow fiber membranes, the maximum stress was 3–5 times higher than those of the CDA and CAP membranes. The temperature gap between the cloud point and crystallization onset in the polymer solution plays a crucial role in membrane formation. All of the CTA, CDA, and CAP membranes had a very porous bulk structure with a pore size of ∼100 nm or larger, as well as pores several hundred nanometers in size at the inner surface. Using an air gap distance of 0 mm, the appropriate organic solvents mixed in an optimized ratio, and a solvent for cellulose derivatives as the quench bath media, it was possible to obtain a CTA MF hollow fiber membrane with high pure water permeance and notably high rejection of 100 nm silica nanoparticles. It is expected that these membranes can play a great role in pharmaceutical separation.

Removal of Organic Dye in Wastewater Using Polyethersulfone Hollow Fiber Membrane

In this study, polyethersulfone (PES) hollow fiber membranes (HFM) were fabricated with different weight percentage (wt. %) of polymer at 16 wt. %, 18 wt. % and 20 wt. %, in order to study the impact of polymer weight percentages on membrane properties and its dye rejection performance. Microfiltration HFM were fabricated by using the laboratory dry-wet spinning method. In order to improve the pore structure of the polymer membrane, 3 wt. % of (PVP) of 8000 M.W. was added in the dope solution. All the fabricated PES hollow fiber membranes were characterized using the Scanning Electron Microscopy (SEM), Atomic Force Microscope (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and the contact angle. The HFM’s performance was evaluated in terms of dye rejection, by using Direct Red 80 dye as substitute of organic dye in wastewater. The results ed that the membrane with higher weight percentage of PES polymer (20 % PES) had thicker separation layer, smoother membrane surface and uniform like pore structures. The membrane with the higher weight percentage of polymer (20% PES) had higher dye rejection percentage (67.33%) and higher permeate flux (10.024 L/m2h) compared to 16 wt. % and 18 wt. %. The results of this study revealed that the weight percentage of polymer in the membrane did affect the membrane properties and its performance.

Janus hollow fiber membranes with functionalized outer surfaces for continuous demulsification and separation of oil-in-water emulsions

An incredible amount of oily wastewater is generated each day all over the world from industrial manufacture and daily life. Numerous attempts have been undertaken to separate these oil/water mixtures, especially those surfactant-stabilized oil-in-water emulsions. Janus membranes with asymmetric wettability are widely regarded as a promising oil/water separation technology with the lowest energy consumption. In this work, we demonstrate the fabrication of Janus hollow fiber membranes (JHFM) with functionalized outer surface for the continuous demulsification and separation of oil-in-water emulsions. Polydopamine and polyelectrolyte are co-deposited onto the outer surface of polypropylene hollow fiber microfiltration membrane to construct a thin charged hydrophilic coating with controllable thickness. The prepared JHFMs are assembled into typical modules which can continuously separate surfactant-stabilized oil-in-water emulsions with high efficiency (recovery ratio >99%, purity >99.8%). The JHFM modules show applicability to both light oil and heavy oil collection in the common cross-flow filtration mode. The influences of operating conditions, including feed flow rate, surfactant content, hydrophilization depth and packing density, are demonstrated in detail on the separation performance. This work is of great significance to the practical application of Janus membranes in the separation of oil/water mixtures, especially surfactant-stabilized oil-in-water emulsions which are intractable to be separated effectively by conventional methods.

INVESTIGATION of COLOR REMOVAL in REAL TEXTILE INDUSTRY WASTEWATER with MEMBRANE BIOREACTOR-ACTIVE CARBON SYSTEM

The textile industry is an industry that consumes large amounts of water during production, contains various chemicals in its wastewater, conventional treatment methods are insufficient to reduce the wastewater pollution level, and has colloidal substances and color problems. Membrane bioreactor systems provide high efficiency in the treatment of textile wastewater and dyestuff removal. Removal of dyestuffs and turbidity in real textile wastewater by using a laboratory-scale membrane bioreactor system was studied. Chemical precipitation was not applied before the biological treatment for the removal of color and other pollutant parameters. A hollow fiber microfiltration membrane module was used in the system. Then a combination with an active carbon filter was created to take the color removal to a higher level. The development of the microorganism composition adapted to the textile industry was observed in the biological reactor. The system was operated with an endless sludge age and a hydraulic retention time of 24 hours. Color measurement transparency index parameter DFZ (DurchsichtsFarbZahl) was measured in a spectrophotometer at wavelengths of 436, 525, and 620 nm (nanometers) according to EN ISO 7887 standards. In the microfiltration permeate water, the color removal were found in 436 nm: 91-95%, 525 nm: 94-98%, 620 nm: 96-99%, and in activated carbon permeate water, the color removal in 436 nm: 96-99% at 525 nm: 95-99%, 620 nm: 96-99%, respectively. Due to the physical separation of the membrane, which is the simplest definition, high efficiencies in color removal have been achieved in the system. The activated carbon system combined with the membrane was found higher efficiency in color removal than the microfiltration output.

Impact of feed concentration on milk protein fractionation by hollow fiber microfiltration membranes in diafiltration mode

• HFM are effective alternatives with superior performance over SWM and CTM. • Optimization of preconcentration of casein fraction before starting diafiltration. • Optimal transmembrane pressure at 0.5 bar regarding mass flow. • Optimal concentration factor at 2.5 regarding specific filtration effort. • Permeate protein concentration and flux were limiting factors at lower or higher CF. Microfiltration (0.1 µm) in the diafiltration mode is performed using hollow fiber membranes (HFM) to separate the casein micelles and whey proteins in skim milk at 10 °C. This method of using HFM has not been widely applied in dairy technology. HFM differ from more established module systems such as ceramic tubular membranes (CTM) and spiral-wound membranes (SWM) in their geometry, flow conditions, and propensity to deposit formation. The objective of this study is to investigate the efficiency of fractionation according to the pre-concentration before starting diafiltration when using ultrafiltration permeate as diafiltration medium for transferring the whey proteins into the permeate. The concentration having constant pressure drop is compared with that having constant feed volume flow. The optimal process conditions are determined based on the following criteria: flux, whey protein transmission, whey protein mass flow, and time required for one volume turnover, i.e., diafiltration step. The process is found to be optimum at a transmembrane pressure of 0.5 bar, constant pressure drop of 1.0 bar m −1 , and concentration factor (CF) of 2.5. At a CF of 3, 80% whey protein depletion was achieved after 2.5 diafiltration steps. Therefore, HFM are confirmed as effective alternatives to SWM and CTM and are optimized in terms of pre-concentration of the casein fraction before starting diafiltration.

Membrane fouling behaviors of ceramic hollow fiber microfiltration (MF) membranes by typical organic matters

Membrane fouling is a prevalent problem faced by all membrane-based applications, which is affected by membrane features, foulant properties and solution chemistry conditions. Here in this study, we explored the fouling behaviors induced by three typical organic matters (Humic acid (HA), Sodium alginate (SA) and Bovine Serum Albumin (BSA)) during the filtration process of two self-made ceramic hollow fiber MF membranes (denoted as Titania and Alumina, respectively), and compared with that of one commercial PVDF MF membrane. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was employed to investigate the interfacial energy between foulants and different membranes. The results indicated that the anti-fouling ability of the three membranes followed the order: Titania > Alumina > PVDF. Further, it was found that regardless of the membrane features, increase of solution pH improved the interfacial free energy and thus mitigating membrane fouling. The addition of Na+ decreased the fouling tendency of HA and SA, but enhanced the fouling behavior by BSA, while Ca2+ can enhance all the fouling tendency of HA/SA/BSA. Co-existence of different organic matters resulted in a more complex fouling variation, which can not be well described with XDLVO theory. Our research is expected to provide a fundamental reference for MF membrane selection in practical application.

A review on hollow fiber membrane module towards high separation efficiency: Process modeling in fouling perspective

Hollow fiber microfiltration (MF) and ultrafiltration (UF) membrane processes have been extensively used in water purification and biotechnology. However, complicated filtration hydrodynamics wield a negative influence on fouling mitigation and stability of hollow fiber MF/UF membrane processes. Thus, establishing a mathematical model to understand the membrane processes is essential to guide the optimization of module configurations and to alleviate membrane fouling. Here, we present a comprehensive overview of the hollow fiber MF/UF membrane filtration models developed from different theories. The existing models primarily focus on membrane fouling but rarely on the interactions between the membrane fouling and local filtration hydrodynamics. Therefore, more simplified conceptual models and integrated reduced models need to be built to represent the real filtration behaviors of hollow fiber membranes. Future analyses considering practical requirements including complicated local hydrodynamics and nonuniform membrane properties are suggested to meet the accurate prediction of membrane filtration performance in practical application. This review will inspire the development of high-efficiency hollow fiber membrane modules.

Preparation of Hydrophilic UHMWPE Hollow Fiber Membranes by Chemically Bounding Silica Nanoparticles

In this work, ultra-high molecular weight polyethylene (UHMWPE) microfiltration hollow fiber membranes prepared via the thermally induced phase separation (TIPS) method were modified by chemically bounding hydrophilic silica (SiO2) nanoparticles onto the surface to improve anti-fouling performance. A range of testing techniques including attenuated total reflection Flourier transformed infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), water contact angle, mechanical test, filtration and anti-fouling performance were carried out to discuss the influence of different modification conditions on the properties of the membranes. The prepared hollow fiber membranes display the significantly excellent performance when the vinyl trimethoxy silane (VTMS) concentration was 13%, the pH value of the hydrolyzate was 4 and the hydrolysis reaction time was 6 h. In particular, the hydrophilicity of modified membranes was improved effectively, resulting in the enhancement of membrane anti-fouling properties. The results of this work can be consulted for improving the anti-fouling performance of the UHMWPE microfiltration hollow fiber membrane applied in the field of water purification.

Removal of Contaminants and Pathogens from Secondary Wastewater Effluents using Hollow Fiber Microfiltration Membranes

The main purpose of this study was to investigate the ability of cross-flow microfiltration technique to treat urban wastewater effluents. Experimental results demonstrated that this technique is reliable and very effective in removing wastewater impurities. Results showed that hollow fiber membranes achieved a significant removal rate of all parameters tested except ammonium nitrogen. This study confirmed that cross-flow microfiltration process is very efficient concerning the abatement of suspended solids and organic matter. All pathogenic bacteria indicators were removed by this process. The experimental study demonstrated that quality of permeate produced by hollow fiber microfiltration membranes is suitable for industrial reuse.

Different techniques for concentration of extracellular biopolymers with herbicidal activity produced by Phoma sp

ABSTRACT The natural ability of microorganisms to secrete high levels of bioactive compounds make them attractive hosts for producing novel compounds. Microbial biopolymers have potential applications in most of the sectors of the world economy. According to the physicochemical properties, they present some advantages, such as biodegradability, reproducibility, and stability. Based on this context, the objective of this work was to evaluate different methods for concentration and characterisation of extracellular biopolymers produced by Phoma sp. Extracellular biopolymers were produced by submerged fermentation and were concentrated by hollow fibre membranes and by adsorption. The structural characterisation of purified biopolymers was determined by Fourier Transform Infrared spectroscopy. Phytotoxic effects were assessed through absorption assays in detached leaves of Cucumis sativus and evaluated on the seventh day after application. The surface tension was evaluated for each sample. Hollow-fibre microfiltration membrane presented a higher purification factor than hollow-fibre ultrafiltration membrane. Extracellular biopolymers were identified in the permeate and retentate fractions, but in higher concentration in the retentate fractions. The adsorption process was efficient for recovering more than 88% of extracellular biopolymers from cell-free fermented broth. The best performance was obtained by using silica and activated carbon as adsorbent, with a recovery higher than 93%. The herbicidal activity was proportional to the concentration of biopolymers and the results are very promising for future applications because a concentrated solution of biopolymers can increase weed control. Membrane processes can be used to develop a liquid formulation of bioherbicide, whereas adsorption can be used to develop a solid formula.

Fabrication and characterization of mullite ceramic hollow fiber membrane from natural occurring ball clay

This work aims to study the physico-chemical and permeation properties of ceramic hollow fiber microfiltration (MF) membranes. Ball clay from Perak, Malaysia was used as an alternative starting material for membrane preparation. The membranes were prepared at various solid loadings (37.5 to 50 wt%) and sintering temperatures (1150 to 1300 °C) via phase inversion-based extrusion/sintering method. Prior to membrane fabrication, the as-received ball clay underwent pre-treatment and was characterized using thermal gravimetric analysis (TGA), laser diffraction particle size analyzer (Metasizer 3000), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Sintered hollow fiber membranes were characterized in terms of crystalline phase using thin-film XRD, surface morphology via scanning electron microscope (SEM), mechanical property using 3-point (3p) method, wall thickness, porosity, pore size distribution and permeation property. XRD patterns show that the ball clay contains 85.9% kaolinite, 9.5% illite, 3.6% quartz and 1% maghemite. After sintering, the major phase of the hollow fiber membranes transformed into mullite (91 to 94%) with minor traces of quartz. The membranes' properties strongly depend on both solid loading and sintering temperature. Moreover, when the hollow fiber membrane with solid loading of 47.5 wt% was sintered at 1250 °C, its mechanical strength (55.8 ± 5.8 MPa) was comparable to that of purity-based ceramic hollow fiber membranes. The membrane has an average porosity and pore size of about 50.5 ± 2.1% and 0.61 μm, respectively, which are within microfiltration range, and has an average pure water flux of 1286 ± 181 L/m2.hr. Compared with its high purity metal oxide ceramic counterparts, this alternative ball clay-based hollow fiber membrane can be sintered at lower sintering temperature while exhibiting comparable mechanical strength and water flux.

EVOH in situ fibrillation and its effect of strengthening, toughening and hydrophilic modification on PVDF hollow fiber microfiltration membrane via TIPS process

In order to enhance the strength and overcome the poor antifouling capacity of poly(vinylidene fluoride) (PVDF) membrane used in water treatment, herein, poly(ethylene-co-vinyl alcohol) (EVOH) was selected and the PVDF/EVOH blend hollow fiber microfiltration membrane was prepared via the thermally induced phase separation (TIPS) technique. The morphology for the pristine and blend membrane was compared, and the distribution of EVOH on outer surface and within matrix was explored. The fibrous-shaped EVOH enhanced the breaking strength of the membrane markedly (up to 13.63 MPa) due to the in situ fibrillation; especially, when the blend membrane was immersed into water, the internal plasticization of water molecular enhanced the toughness of the membrane and the elongation at break increased up to 86.39% compared with 27.63% for the corresponding dry membrane and 36.62% for the pristine membrane, respectively. The addition of EVOH introduced hydroxyl group into the bulk and thus endowed the membrane with a better hydrophilicity (the contact angle is as low as 43°) and higher pure water flux (up to 449.11 L m−2 h−1) compared with pristine PVDF membrane. Moreover, the blend membrane showed a better rejection of carbonic particle (nearly 100%) and higher flux recovery rate (up to 87.30%). The present investigation offers an effective and simple pattern to regulate microstructure and enhance mechanical strength, flux and hydrophilicity of the polymeric microfiltration membrane via the TIPS process for water treatment.

Fabricating PVDF hollow fiber microfiltration membrane with a tenon-connection structure via the thermally induced phase separation process to enhance strength and permeability

In this work, thermally induced phase separation (TIPS) method was adopted to manufacture polyvinylidene fluoride (PVDF) blend hollow fiber microfiltration membrane with tenon-connection structure, which is used to fasten in Chinese traditional building by the stronger friction between rabbet and mortise, for water treatment by blending polyvinyl butyral (PVB). In this microstructure formation process, the distribution of PVB within the matrix and its regulatory role were investigated. Especially, the comprehensive effect of rabbeting and PVB adhesion on strength (The maximum breaking strength reached 17.08 MPa) was discussed. The results showed that a suitable PVB will markedly reduce the thickness of skin-layer close to the outside surface even for the solid-liquid (S-L) phase separation while the excessive PVB result in a thick skin-layer. Besides the strength, PVB markedly improved the hydrophilicity and permeability of the membrane. The breaking strength is more than 8 MPa, the maximum pure water flux is as high as 929.23 L m−2 h−1 and the rejection rate of carbon particles is nearly 100% even the polymer content is only 22%. In addition, the membrane showed a β-phase and an improved anti-fouling capacity. The investigation presented a simple way to regulate microstructure, enhance mechanical strength, flux and anti-fouling capacity of the membrane via the TIPS process for water treatment.

Digestion performance and contributions of organic and inorganic fouling in an anaerobic membrane bioreactor treating waste activated sludge

This study evaluates the performance of an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge. A digestion reactor equipped with an external hollow fiber microfiltration membrane module was operated in continuous-mode for 248 days. The system demonstrated 56% volatile solids degradation at an organic loading rate of 0.40 g-VS/(L·d) in 15 days of hydraulic retention time. The average methane content in the biogas produced was 76% which is considerably high compared to that from a typical continuously stirred tank reactor. The transmembrane pressure remained under 12 kPa without membrane cleaning during the experimental period due to low filtration flux (0.01–0.07 m/d) and cross-flow-mode filtration. Ex situ membrane cleaning revealed that physically irreversible fouling was the dominant form of membrane fouling. Inorganic and organic fouling accounted for 16% and 45% of total membrane fouling, respectively.

A novel γ-Al2O3 nanofiltration membrane via introducing hollow microspheres into interlayers for improving water permeability

Ceramic nanofiltration (NF) membranes with high resistance to harsh environments have been widely studied and applied in various fields, involving food, bioengineering and water purification. In this work, γ-Al2O3 hollow microspheres with mesoporous shell structures served as an interlayer on a high-flux α-Al2O3 hollow fiber microfiltration (MF) membrane to increase porosity and permeability. Here, the boehmite sol was made from the pseudo-boehmite precursor with a mild and environment friendly feature, instead of the conventional methods using aluminum alkoxides. The self-assembled microspheres (SAMs) mixture and boehmite sol were applied to make an interlayer and toplayer successively on α-Al2O3 substrates by dip-coating. Where, the SAMs constructed by poly-(styrene-acrylic acid) (PSA) microspheres and boehmite colloidal particles could stop the boehmite sol from permeating into inner pores of the support. Next, the composite membranes were calcined to remove organic components and finish the decomposition of the Al hydroxides at 600 °C for 2 h. The results show that the γ-Al2O3 composite NF membrane has a high pure water permeability of 26.4 L m−2 h−1 bar−1, with high retention rate for multivalent cations and low retention rate for monovalent cations, respectively, and the molecular weight cut-off (MWCO) of approximately 1500 Da.