Hollow Fiber Microfiltration Research Articles

A microtubular all CNT gas diffusion electrode

We report a microtubular gas diffusion electrodes made of multi-walled carbon nanotubes (MWCNT). The electrodes were prepared by inside-out cake filtration of an aqueous MWCNT suspension onto a microfiltration hollow fiber (HF) membrane, followed by washing out the surfactant, drying and removal of the all CNT microtube from the HF membrane. Length, outer diameter, and wall thickness of the tubular electrodes are: up to 44cm, ~1.7mm and 275μm, respectively. The BET surface area is 200m2/g with a porosity of 48–67% and an electrical conductivity of~20S/cm. Application of this microtubular Gas Diffusion Electrodes (GDE) was studied for the oxygen reduction reaction (ORR) in divided and undivided electrochemical cells. Oxygen supply into the lumen of the tubular electrodes resulted in much higher current densities for ORR than in experiments where the electrolyte was saturated by bubbling with pure oxygen. Within the 0.25–1.0bar pressure (gauge) region, higher ORR rates were achieved at lower pressure. We also show that H2O2 production is possible using the new GDE. We propose to use such novel electrodes for the fabrication of tubular electrochemical reactors, e.g. fuel cells, H2O2 generators, CO2 reduction and other processes that involve GDE application.

Accelerated testing for fouling of microfiltration membranes using model foulants

Hollow fiber microfiltration (MF) membranes have been widely employed for water and wastewater treatment. Nevertheless, membrane fouling is still one of the most serious issues in operating hollow fiber membrane systems. In this research, fouling of hollow fiber MF membranes was evaluated by means of accelerated testing experiments. A single fiber filtration unit was used to perform the fouling experiments in an accelerated way. Permeate flux and foulant concentrations were used as fouling control parameters to adjust the rate of fouling. Four model foulants used were kaolin, silica, natural organic matters (NOM), and alginate. A simple theoretical model was applied to investigate the fouling characteristics of the membrane by the model foulants. The analysis showed that there was a nonlinear correlation between the fouling rate and the fouling control parameters. The “normalized” fouling rate, θ/J2, was found to be useful to quantify the fouling rate and to implement a long-term simulation of TMP changes.

Submerged hollow fiber microfiltration as a part of hybrid photocatalytic process for dye wastewater treatment

In this study, photocatalytic degradation of an organic azo dye, Acid Red 1, has been measured under UV irradiation in an aqueous dispersion of TiO2 to find optimal conditions for a photocatalytic membrane reactor (PMR) operation.Furthermore, to separate and recover the anatase TiO2 photocatalyst, low-pressure microfiltration using hollow fiber membranes was applied. Since the main limitation in dead-end microfiltration with hollow fibers is the formation of an external specific deposit on the outer surface of the membrane, cake layer formation was also studied.The changes in various parameters, including decolorization, chemical oxygen demand, total organic carbon, pH and turbidity of the solution were measured and analyzed during the process. Experimental results indicate that the solutions containing the model azo dyes could be successfully decolorized using the photocatalytic process studied.

해수담수화 전처리로서 가압식 MF 공정의 최적 운전조건 도출

The relation between performance maintenance conditions and those cost efficiency was studied to choose an optimum operating condition in the seawater desalination pretreatment system. A hollow fiber microfiltration module, which was developed with domestic technology, was tested with the various operating conditions such as chemically enhanced backwash cycles and design dosages of a cleaning chemical. Transmembrane pressure was measured to investigate membrane fouling status and cleaning degree. In addition, economic analysis was performed to compare water production costs by the operation condition. As a result, The operation mode III, chemically enhanced backwash at once a day with 100 mg/L of sodium hypochlorite (NaOCl) was selected. The concurrent evaluation between membrane filtration performance and its economic analysis will be suitable to choose an efficient optimum condition.

Assessment of an anaerobic membrane bio-electrochemical reactor (AnMBER) for wastewater treatment and energy recovery

Microbial fuel cells (MFCs) have a great potential for cost-effective wastewater treatment; however, the effluent quality from MFC is not always satisfied. In this study, an anaerobic membrane bio-electrochemical reactor (AnMBER) with an anaerobic membrane bioreactor (AnMBR) equipped with hollow-fiber microfiltration (MF) membranes directly serving as the cathodic chamber of a dual-chamber MFC was developed. Over an operational period of more than 600h, the AnMBER system (with 100Ω resistor) was able to generate continuous bio-electricity (0.132V), with a maximum power density of 1.16Wm−3 net cathodic chamber (NCC), and achieved high removal efficiencies of chemical oxygen demand (COD) (91.6%) and nitrate (94.8%). Furthermore, compared with a control AnMBR (with open circuit), membrane fouling was mitigated significantly in the AnMBER system, which was mainly attributed the lower particle zeta potential and lower amount of soluble microbial products (SMP) in the cathodic mixed liquor. These results demonstrate that integrating the anaerobic MF filtration sequentially to MFCs is a feasible approach to accomplish simultaneous efficient wastewater treatment and energy recovery and also raises the possibility of using MFCs as a means to minimize fouling in combined systems by improving the mixed liquor properties.

Positively charged thin-film composite hollow fiber nanofiltration membrane for the removal of cationic dyes through submerged filtration

Positively charged thin-film composite hollow fiber nanofiltration membranes were developed by the dip-coating method using polypropylene hollow fiber microfiltration membrane as support, polyvinyl alcohol (PVA) and polyquaternium-10 (the reaction product of hydroxyethyl cellulose with a trimethylammonium substituted epoxide, PQ-10) as coating materials, and glutaraldehyde as cross-linking agent. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), measurements of streaming potential and contact angle were employed to characterize the obtained membranes. The permeation properties were estimated through pressurized cross-flow permeation tests and the dye removal performance were evaluated through submerged filtration tests using cationic dye aqueous solutions. It was found that the salt rejection order of the membrane was CaCl2>MgCl2>NaCl>MgSO4>Na2SO4 at neutral pH. The desired membrane with a molecular weight cut-off of about 650Da had a pure water flux of 25.7l/m2h and a rejection of 92.8% to 500mg/l CaCl2 aqueous solution at 3.0bar. The membrane could effectively remove cationic dyes from aqueous solution with good long-term performance stability through submerged filtration. The observed rejections to Brilliant green, Victoria blue B and Crystal violet were 99.8, 99.8 and 99.2%, respectively, under the trans-membrane pressure of 0.7bar.

HYDRAcap® MAX: innovative micro-filtration for reverse osmosis pretreatment and water reuse

Hydranautics has been a manufacturer of organic membranes for more than 30 years and has always been a technology leader. Being part of the Nitto Denko Group since 1987, hydranautics has inherited Nitto Denko’s innovative philosophy. In September 2011, hydranautics announced the commercialization of its new PVDF hollow fiber microfiltration module: HYDRAcap® MAX. This new out/in module features one of the highest membrane areas currently available in the industry. Furthermore, HYDRAcap® MAX offers an air scour (AS) mode that allows the designer to eliminate the backwash sequence and pump; this results in increased recovery and lower capital expenses. The key applications for HYDRAcap® MAX are reverse osmosis pretreatment and water reuse, for both industrial and municipal applications from various types of water sources.This study will introduce HYDRAcap® MAX technology and its advantages, including higher membrane area resulting in lower footprint and innovative design resulting in optimized recovery. It will also discuss the operating sequences (i.e. filtration, AS, and cleanings), provide data from a case study, and give an example of a medium size system.

침지형 MBR공정에서 파울링 특성과 파울링 완화제의 적용성에 관한 연구

Though MBR process has many advantages, the greatest risk factors in operating MBR process are occurrence of membrane fouling and decrease of flux. It is very difficult to find exact mechanism due to complex influence by many effects, although there have been recently many studies of membrane fouling. The purposes of this study are firstly evaluating bioreactor of lab-scale and micro-filtration hollow fiber membrane, secondly investigating correlation between foulants affecting membrane performance and membrane fouling, and lastly evaluating various parameters affecting fouling and applicability of membrane fouling reducer. This study found that TMP was increasing rapidly and showed 0.32 bar and the average of flux was 88 LMH. EPS concentration tends not to change much above MLSS concentration (6,000 mg/L). However, EPS concentration variation is wide below MLSS concentration (6,000 mg/L). Also, from results of membrane surface condition and element analysis using SEM/EDX, carbon and fluorine were founded to be the highest percentage in membrane because of characteristics of membrane material. In operating continuously, inorganic fouling was generated by increase of these inorganic substances such as and . Lastly, the best filtration performance was obtained for 0.03 mg MFR/mg MLSS by results of particle size, zeta potential, , EPS and MLSS concentration.

A feasibility study on UV pretreatment for microfiltration and reverse osmosis membrane processes in wastewater reclamation

Wastewater reclamation is where wastewater from various sources is purified so the water can be used by human consumption. Among many treatment options, membranes have gained an important place in wastewater reclamation. It allows the production of high quality water from wastewater, with a small footprint and affordable energy consumption. Nevertheless, membrane fouling is regarded as a serious problem due to the high fouling potential of wastewater. In this study, we applied ultraviolet (UV) processes as a pretreatment for membrane systems that are used for wastewater reclamation. Low pressure UV (LUV) and pulsed UV (PUV) were used to decompose or alter the organics in the feed water of the membranes. Effluent organic matter was characterized by total organic carbon (TOC) and UV absorbance (UVA). Also the effect of UV pretreatment on membrane fouling was investigated for microfiltration (MF) and reverse osmosis (RO) processes. The pretreatment of membranes using LUV or PUV was effective to control fouling of hollow fiber MF membranes. This is probably because of the reduction and modification of organics after UV treatments. However, the effect of UV pretreatment on RO flux was less significant, which is attributed to low fouling prophecy after MF treatment.

Membrane installation for enhanced up-flow anaerobic sludge blanket (UASB) performance

It is postulated that up-flow anaerobic sludge blanket (UASB) reactor efficiency can be enhanced by a membrane immersed in the reactor to operate it as an anaerobic membrane bioreactor (AnMBR) for low-strength wastewater treatment. This postulate was tested by comparing the performance with and without a hollow fiber microfiltration membrane module immersed in UASB reactors operated at two specific organic loading rates (SOLR). Results showed that membrane filtration enhanced process performance and stability, with over 90% total organic carbon (TOC) removal consistently achieved. More than 91% of the TOC removal was achieved by suspended biomass, while less than 6% was removed by membrane filtration and digestion in the membrane attached biofilm during stable AnMBRs operation. Although the membrane and its biofilm played an important role in initial stage of the high SOLR test, linear increased TOC removal by bulk sludge mainly accounted for the enhanced process performance, implying that membrane led to enhanced biological activity of the suspended sludge. The high retention of active fine sludge particles in suspension was the main reason for this significant improvement of performance and biological activity, which led to decreased SOLR with time to a theoretical optimal level around 2g COD/g MLVSS·d and the establishment of a microbial community dominated by Methanothrix-like microbes. It was concluded that UASB process performance can be enhanced by transforming such to AnMBR operation when the loading rate is too high for sufficient sludge retention, and/or when the effluent water quality demands are especially stringent.

Gravity driven membrane filtration system to improve the water quality in rainwater tanks

The characterisation of rainwater in metropolitan Sydney and in rural New South Wales was undertaken. The results showed that factors such as the lack of vehicular traffic, air pollution and urban contamination meant that rural rainwater water quality was better. The rain water collected in both metropolitan and rural areas generally complied with the 2004 Australian Drinking Water Guidelines except for parameters such as the pH in both the metropolitan and rural rainwater tanks and the turbidity, and lead levels from the metropolitan tanks. This paper also reports the results of a laboratory and a pilot scale study with a deep bed filter (granular activated carbon, GAC) and microfiltration (MF) hollow fibre membrane filter system used to treat raw rainwater collected from a metropolitan rainwater tank. The results of the laboratory experiment and pilot scale systems focus on the non-compliant parameters of the sampling program, i.e. turbidity, lead and dissolved organic carbon (DOC). It was found that rainwater treated by the GAC filter removed the majority of the turbidity and organic substances. The treatment system reduced the concentration of turbidity, lead and DOC to below the Australian Drinking Water Guidelines limits. The pilot plant experiment demonstrated that a GAC filter system and gravity driven membrane could result in low cost and low maintenance operation.

Combined effects of EPS and HRT enhanced biofouling on a submerged and hybrid PAC-MF membrane bioreactor

The goal of this study was to quantify and demonstrate the dynamic effects of hydraulic retention time (HRT), organic carbon and various components of extracellular polymeric substances (EPS) produced by microorganisms on the performance of submersed hollow-fiber microfiltration (MF) membrane in a hybrid powdered activated carbon (PAC)-MF membrane bioreactor (MBR). The reactors were operated continuously for 45 days to treat surface (river) water before and after pretreatment using a biofiltration unit. The real-time levels of organic carbon and the major components of EPS including five different carbohydrates (d(+) glucose and d(+) mannose, d(+) galactose, N-acetyl-d-galactosamine and d-galactose, oligosaccharides and l(−) fucose), proteins, and polysaccharides were quantified in the influent water, foulants, and in the bulk phases of different reactors. The presence of PAC extended the filtration cycle and enhanced the organic carbon adsorption and removal more than two fold. Biological filtration improved the filtrate quality and decreased membrane fouling. However, HRT influenced the length of the filtration cycle and had less effect on organic carbon and EPS component removal and/or biodegradation. The abundance of carbohydrates in the foulants on MF surfaces was more than 40 times higher than in the bulk phase, which demonstrates that the accumulation of carbohydrates on membrane surfaces contributed to the increase in transmembrane pressure significantly and PAC was not a potential adsorbent of carbohydrates. The abundance of N-acetyl-d-galactosamine and d-galactose was the highest in the foulants on membranes receiving biofilter-treated river water. Most of the biological fouling compounds were produced inside the reactors due to biodegradation. PAC inside the reactor enhanced the biodegradation of polysaccharides up to 97% and that of proteins by more than 95%. This real-time extensive and novel study demonstrates that the PAC-MF hybrid MBR is a sustainable technology for treating river water.

Removal of cyanobacterial cells and Microcystin-LR from drinking water using a hollow fiber microfiltration pilot plant

Various species of cyanobacteria may produce cyanotoxins, bad smell and taste and cause a deterioration of the water's sensory characteristics and serious harmful effects on human health. This study investigates the possibility of removing total algae and cyanobacteria from lake water by means of a hollow fiber microfiltration pilot plant (2–4m3/h). The influence of these treatments on water chemical and microbiological quality was evaluated too. Among the seventeen species of cyanobacteria analyzed, the highest density in the feed water was observed for Anabaena lemmermannii while the species most frequently detected was Microcystaceae D5. Microfiltration was able to achieve removal rates higher than 98% for a large number of species of cyanobacteria and the removal efficiency of total algae content was about 98–99%. Moreover, no release of toxins into the permeate water was observed during water treatment. Microfiltration was able to guarantee also good removal yields for turbidity (>90%), suspended solids (yield >80%) and organic compounds (yield of about 70% for UV absorbance at 254nm).

Structure-performance-fouling studies of polysulfone microfiltration hollow fibre membranes

Hollow fibre microfiltration membranes were prepared by solution spinning process using polymer dope containing different amounts of polysulfone (PS), polyvinylpyrollidone (PVP) and \({\bf \textit{N}}\), \({\bf \textit{N}}\)-dimethylformamide (DMF). Spinning dope having PS: PVP: DMF (w/w) of 15: 5: 80, 15: 7: 78 and 17: 8: 75 were used for spinning to obtain hollow fibres having different dimensions (outer and inner diameters) and pore characteristics. Relatively high water permeability was observed for hollow fibre membrane spun from 15 wt. % solution than 17 wt. % PS solution having the same PVP/PS ratio of 0·47. Decrease of the PVP/PS ratio to 0·33 in the dope solution of 15 wt. % PS solution produced hollow fibre membrane with lower flux. By changing the spinning parameters, fibre with different dimensions were obtained without a significant change in microstructural morphology. The flux decline due to fouling for the permeation of PEO/BSA solution was maximum for the hollow fibre membrane obtained from 15 wt. % PS solution while a steady flux with slight fouling was observed for the hollow fibre membrane obtained from 17 wt. % PS solution, when the PVP/PS ratio was 0·47.

A novel ultrafiltration (UF) membrane with controllable selectivity for protein separation

A novel ultrafiltration (UF) membrane with controllable selectivity for protein separation was obtained by altering the structure of the thick sieving layer on the membrane surface and subsurface. Poly(vinyl pyrrolidone) (PVP) was first cross-linked on/in the poly(vinylidene fluoride) (PVDF) hollow fiber microfiltration (MF) membrane to attract more sulfobetaine (SB) monomer adjacent to membrane for subsequent grafting polymerization and the formed thick sulfobetaine polymer (PSB) layer on the membrane surface and subsurface acted as the sieving layer with environment sensitivity. After immersed in 20mmol/L NaCl solution at 60°C, the novel UF membrane with the sieving layer of 4.8μm showed high permeate capacity with a water flux of 590L/m2h and a good selective behavior with MWCO of 95–110kDa. The protein mixture (BSA and Lys) could be separated through the novel UF membrane efficiently by isoelectric focusing of one component with a larger size (BSA). By means of the simple immersion in pure water, the membrane permeated most of proteins and the degree of flux decline reduced obviously. After swelled in NaCl solution again, the membrane restored the selectivity and the protein separation efficiency. Such novel smart UF membrane is an attractive candidate for the batch separation of protein mixtures, expanding the membrane application in the fields of agro-food, biomedicine and other bio-filtration.

Selective capture of anti‐A antibodies from human blood using a novel integrated bead and hollow fiber module

Anti-A/B antibody removal from blood in the peritransplantation period facilitates ABO-incompatible transplantation and significantly increases the donor pool. We have been developing an anti-A/B immunoadsorption device (BSAF), compatible with whole blood perfusion. The BSAF is based on integrated microfiltration hollow fibers with antibody capturing beads uniformly distributed within the fiber interstitial space. In this study we fabricated BSAF prototypes, appropriately scaled down from a conceptual clinical scale device. We then, for the first time, measured the time course of anti-A capture from blood samples recirculating through the scaled down BSAF devices. We observed a significant reduction in IgM (96% ± 5%, n = 5, p < 0.001), and IgG (81% ± 18%, n = 5, p < 0.05) anti-A antibody titers within 2 h. We did not observe a significant change between the initial and final values of hematocrit, total plasma protein concentration, plasma free hemoglobin concentration, and anti-B antibody titer over five experiments. In conclusion we showed that the BSAF modules selectively removed anti-A antibodies from blood in a simple one step process, without requiring a separate plasmapheresis unit.

Generation of Dean vortices and enhancement of oxygen transfer rates in membrane contactors for different hollow fiber geometries

This work aimed to study the enhancement of oxygen transfer rates in hollow fiber membrane contactors by applying Dean vortices. Systematic investigations of how the geometric parameters, like curve diameter, helical pitch or geometric shape, and flow rates affect the mass transport were done to assess the potential for membrane contactors. The membrane was a hydrophobic microfiltration hollow fiber (polypropylene). Helical, meander and twisted formed hollow fibers with fiber lengths from 5 to 30cm and curvature diameters between 5 and 19mm were constructed. The oxygen transfer rates per membrane area were investigated. The curved hollow fibers show a linear dependence between Dean number and enhancement factor and an increase of transfer rates up to an enhancement factor of 2.4. For the meander shaped fibers a critical Dean number/range between 10–20 was found, where the mass transport enhancement is adjusted rapidly to those of helical hollow fibers. Also the mass transfer in packed membrane modules was investigated, taking into account the theoretical packing densities of the different fiber geometries. It was found that a volumetric enhancement of gas transfer rates for helical and meander formed fibers can only be improved applying very small curvature diameters less than 4mm.

Buckminsterfullerene (C60) nanoparticle fouling of microfiltration membranes operated in a cross-flow configuration

Manufactured nanomaterials, like buckminsterfullerene (C60), present unique challenges with regards to their impacts on the performance of microfiltration (MF) membranes. Of particular concern is the ability of existing physical and chemical cleaning processes to remove nanoparticle deposits on the surface and from the interior of MF membranes. The objective of this research was therefore to characterize C60 nanoparticle fouling of hollow fiber MF membranes and assess the ability of hydraulic backwashing and different cleaning solutions to remove nanoparticle deposits from fouled MF membranes. Two nanoparticles, a manufactured C60 and a carboxylated nanosphere, were studied and found to similarly affect membrane performance. Nanoparticle fouling resulted in a more substantial impact on membrane performance relative to that resulting from a colloidal foulant. This was attributed to the ability of the nanoparticles to form comparatively more dense surface deposits and to pass through the MF membrane resulting in standard pore blocking and cake layer formation on the filtrate side of the membrane. Using nanoparticle free backwash water was found to remove these cake structures on the filtrate side of the membrane and to displace the internal nanoparticle deposits. The C60 cake structures were poorly removed using conventional cleaning solutions, with the exception of hydrogen peroxide; however, removal with the hydrogen peroxide was incomplete and resulted more rapid fouling after normal operation was resumed.

Facile modification of polypropylene hollow fiber microfiltration membranes for nanofiltration

Modification of polypropylene (PP) hollow fiber microfiltration membranes for nanofiltration through dip-coating sodium carboxymethyl cellulose (CMCNa) skin layer followed by cross-linking with AlCl3 was investigated in this study. Modification parameters were studied to optimize the membrane performance and the obtained modified membranes were characterized in terms of surface and permeation properties. It was found that the surface property and solute separation capability of the PP hollow fiber membrane were significantly improved by coating CMCNa surface layer, and the optimized modified membrane took on a composite structure with a hydrophilic selective skin layer having an isoelectric point of pH 3.7. The composite layer was negatively charged at neutral pH and was relatively looser in acidic pH compared with that in basic or neutral. Permeation tests revealed that the desired modified membrane possessed a molecular weight cut-off (MWCO) of 760Da and a high pure water permeability of 10.8l/m2hbar, and exhibited rejections to salts following the order of MgCl2<CaCl2<MgSO4<NaCl<KCl<Na2SO4 at neutral pH. Additionally, the modified membrane could efficiently remove anionic dyes from saline aqueous with good long-term performance stability. Retentions to Congo red and Methyl blue were 99.8% and 99.6%, respectively, under neutral pH and 3.0bar.

Compartmental Hollow Fiber Capillary Membrane–Based Bioreactor Technology for In Vitro Studies on Red Blood Cell Lineage Direction of Hematopoietic Stem Cells

Continuous production of red blood cells (RBCs) in an automated closed culture system using hematopoietic stem cell (HSC) progenitor cell populations is of interest for clinical application because of the high demand for blood transfusions. Previously, we introduced a four-compartment bioreactor that consisted of two bundles of hollow fiber microfiltration membranes for transport of culture medium (forming two medium compartments), interwoven with one bundle of hollow fiber membranes for transport of oxygen (O(2)), carbon dioxide (CO(2)), and other gases (forming one gas compartment). Small-scale prototypes were developed of the three-dimensional (3D) perfusion cell culture systems, which enable convection-based mass transfer and integral oxygenation in the cell compartment. CD34(+) HSC were isolated from human cord blood units using a magnetic separation procedure. Cells were inoculated into 2- or 8-mL scaled-down versions of the previously designed 800-mL cell compartment devices and perfused with erythrocyte proliferation and differentiation medium. First, using the small-scale 2-mL analytical scale bioreactor, with an initial seeding density of 800,000 cells/mL, we demonstrated approximately 100-fold cell expansion and differentiation after 7 days of culture. An 8-mL laboratory-scale bioreactor was then used to show pseudocontinuous production by intermediately harvesting cells. Subsequently, we were able to use a model to demonstrate semicontinuous production with up to 14,288-fold expansion using seeding densities of 800,000 cells/mL. The down-scaled culture technology allows for expansion of CD34(+) cells and stimulating these progenitors towards RBC lineage, expressing approximately 40% CD235(+) and enucleation. The 3D perfusion technology provides an innovative tool for studies on RBC production, which is scalable.