Hollow Fiber Membrane System Research Articles

Effect of recycle ratio on the cost of natural gas processing in countercurrent hollow fiber membrane system

The separation of the countercurrent hollow fiber membrane module has been characterized adapting a “Multi-component Progressive Cell Balance” approach and incorporated within the Aspen HYSYS process simulator. The simulated data is found to exhibit good accordance with published experimental result. The study of the double staged membrane module with permeate recycle system, which was proposed to be the optimum configuration in previous works, has been extended by altering the recycle ratio of the permeate stream to study the process economics. Parameter sensitivities of typical membrane selectivity and CO2 feed concentration adapted in industrial application have been conducted. The study of high CO2 content is highlighted since it represents the future expansion of natural gas extraction considering that most of the remaining fields contain high concentration. It is observed that the recycle ratio is an important parameter to be considered in the industrial design process since it affects the gas processing cost significantly. Increasing the recycle ratio is proposed to increase the membrane area and compressor power while improving the hydrocarbon recovery, with substantial impact observed at low selectivity membrane and high CO2 feed concentration. A tradeoff must be determined among these parameters for determination of the optimal recycle ratio configuration.

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.

A Porous Media Approach for Hollow Fiber Transport Phenomena

A porous media approach based on the volume averaging theory has been proposed to investigate membrane transport processes associated with hollow fiber dialyzers and radial flow hollow fiber reverse osmosis module. A general set of macroscopic governing equations has been derived for the three individual phases, namely, the lumen side flow phase, shell side flow phase and membrane phase. Analytical and numerical solutions based on the present approach are found to agree well with available experimental data. Three-dimensional numerical models can be used for possible optimization of the hollow fiber membrane systems.

Pulse bubble sparging for the control of hydraulically reversible fouling in submerged hollow fiber membrane systems

Previous studies have demonstrated that pulse bubble sparging is more effective at the control of hydraulically reversible fouling than coarse bubble sparging in submerged hollow fiber membrane systems. However, some of the optimal operating set points for pulse bubble sparging control have not yet been identified. The present study was conducted to further quantify the potential benefits associated with pulse bubble sparging for the control of hydraulically reversible fouling. In particular, the effect of pulse bubble release frequency and size on the shear stress induced onto membranes and the resulting effect on the control of hydraulically reversible fouling was assessed. The shear stress and fouling control resulting from continuous and intermittent coarse bubble sparging was also considered so that the performance of these conventionally used sparging approaches could be compared directly to those for pulse bubble sparging.The shear stress resulting from pulse bubble sparging was significantly greater than that induced by continuous coarse bubble sparging, and similar to that induced by intermittent coarse bubble sparging. However, for pulse bubble sparging, the rate of fouling was significantly lower than for either continuous or intermittent coarse bubble sparging, indicating that the magnitude of the shear stress on its own cannot be used to assess the efficacy of different sparging approaches for the control of hydraulically reversible fouling.The pulse bubble release frequency had a significant effect on the rate of fouling. At lower sparging flows (i.e. lower pulse bubble release frequencies), the fouling rate decreased as the sparging flow increased. However, at the highest sparging flow considered, the rate of fouling was greater than that observed at the lower sparging flows, indicating that an optimal bubble release frequency likely exists, below which an increase in frequency decreases the extent of hydraulically reversible fouling, and above which the control of hydraulically reversible fouling is inhibited. For the conditions investigated, a pulse bubble release frequency of approximately 0.5–0.6Hz was optimal. In addition, the results suggest that the optimal pulse bubble size for the control of hydraulically reversible fouling is likely in the 150–250mL range. Sparging into stagnant water also resulted in better hydraulically reversible fouling control than sparging when liquid upflow was promoted.

Cr(VI) and azo dye removal using a hollow-fibre membrane system functionalized with a biogenic Pd-magnetite catalyst

This study investigates the application of a hybrid system combining hollow-fibre membrane technology with the reductive abilities of magnetic nanoparticles for the remediation of toxic Cr(VI) and the azo dye, Remazol Black B. Nano-scale biogenic magnetite (Fe3O4), formed by microbial reduction of the mineral ferrihydrite, has a high reductive capacity due to the presence of Fe(II) in the mineral structure. The magnetic nanoparticles (∼ 20 nm) can be arrayed with Pd0 nanoparticles (∼ 5 nm) making a catalytically active nanomaterial. Membrane units, with and without nanoparticles, were challenged with either Cr(VI) or azo dye and some were supplemented with sodium formate, as an electron donor for contaminant reduction promoted by the Pd. The combination of Pd-magnetite with formate resulted in the most effective remediation strategy for both contaminants and the lifetime of the membrane unit was also increased, with 55% (19 days) and 70% (23 days) removal of the azo dye and Cr(VI), respectively. Low flow rates of 0.1 ml/min resulted in improved efficiencies due to increased contact time with the membrane/nanoparticle unit, with 70–75% removal of each contaminant. Chemical analyses of the nanoparticles post-exposure to Cr(VI) in the membrane modules indicated Pd to be more oxidized when Cr removal was maximized, and that the Cr was partially reduced to Cr(III) at the surface of the magnetite. These results have demonstrated that hollow-fibre membrane units can be enhanced for the removal of soluble, redox sensitive contaminants by incorporation of a layer of palladized biogenic nanoparticulate magnetite.

An analytical index for evaluating manufacturing cost and performance of low-pressure hollow fibre membrane systems

Water and waste-water treatment through the use of the membrane filtration technology is one of the processes utilized currently to meet the growing demand for water. While new technologies can harness water from various non-traditional sources such as oceans, there remains the possibility of making drinking water more expensive through the use of costly water treatment equipment. To prevent this and ensuing catastrophes in the world, the water industry needs a strategy that keeps the price of water and price of products aiding the treatment of water controlled in to the future.This paper firstly presents the need for the industry to focus on controlling the price of water. Secondly, since the paper focuses on low pressure hollow fibre membranes, the processes used for the manufacture of Memcor® membrane modules, from material preparation to packaging and testing are explained. Thereafter, through referencing the Memcor membrane module manufacturing process, an analytical model to determine the membrane module cost and membrane performance is presented. The model leads to the presentation of the Water Price Index (WPI) which is an index that evaluates the membrane module price against its design flux, expected life and efficiency. By targeting a low WPI, the water industry can control the price of water and water treatment equipment. Analysis indicates that membrane design flux and expected life are the key drivers in keeping a low WPI. The paper concludes after presenting results of a factorial study and recommending further research subjects.

Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash

The filtration behavior and energy consumption of submerged hollow fiber membranes were investigated in a dead-end mode under constant flux operation with periodic backwash. Various operating parameters such as filtration flux, feed concentration, backwash duration, backwash strength, and the aid of air scouring during backwash were investigated to optimize the filtration performance and energy consumption. Baker's yeast was used as the model foulant. The transmembrane pressure (TMP) profiles obtained with this model foulant indicated the existence of two regions: a low fouling region followed by a high fouling region. In the low fouling region, periodic backwash could effectively remove the fouling layer. The percentage of reversible fouling by backwash was significantly lower in the second region which led to a rapid increase in TMP. The Taguchi experimental design method was used to determine the critical parameters, the effect of individual parameters and the optimum conditions. Since the transition into the second region of filtration is not favorable, the fouling rate in the first 10 cycles, the net permeate volume and specific energy consumption at the end of the first region were chosen as the design method responses. The results showed that filtration flux and feed concentration have significant effects on the membrane fouling rate. In order to maximize the net permeate volume, filtration flux, backwash duration and backwash strength were found to be the most important parameters, which must be carefully selected. To minimize the specific energy consumption, filtration flux, backwash duration and aeration rate during backwash were the most important factors.

Support media impacts on humic acid, cellulose, and kaolin clay in reducing fouling in a submerged hollow fiber membrane system

The impact of support media on a submerged hollow fiber PVDF ultrafiltration membrane system filtering synthetic water with different organic and inorganic matter content was investigated using a factorial design of experiments. Support media was added into a membrane reactor where membrane fouling and water quality parameters were assessed. The addition of support media into the membrane reactor resulted in a 35–50% reduction in membrane fouling with different humic acid and kaolin clay concentrations compared to the control system with no media; however there was no apparent impact of support media in minimizing fouling by cellulose. The support media in the membrane reactor did not affect any of the water quality parameters measured; however, there was a small but measurable difference in the permeate volume and flux recovery (4% flux difference) between the two systems. This favorable difference was attributed to the presence of support media in the membrane reactor.

Analysis of hollow fibre membrane systems for multicomponent gas separation

This paper analysed the performance of a membrane system over key design/operation parameters. A computation methodology is developed to solve the model of hollow fibre membrane systems for multicomponent gas feeds. The model represented by a nonlinear differential algebraic equation system is solved via a combination of backward differentiation and Gauss–Seidel methods. Natural gas sweetening problem is investigated as a case study. Model parametric analyses of variables, namely feed gas quality, pressure, area, selectivity and permeance, resulted in better understanding of operating and design optima. Particularly, high selectivities and/or permeabilities are shown not to be necessary targets for optimal operation. Rather, a medium selectivity (<60 in the given example) combined with medium permeance (∼300–500×10−10mol/sm2Pa in the given case study) is more advantageous. This model-based membrane systems engineering approach is proposed for the synthesis of efficient and cost-effective multi-stage membrane networks.

Characterization of secondary treated effluents for tertiary membrane filtration and water recycling

This study evaluates the impacts of water quality from three different secondary effluents on low pressure membrane fouling. Effluent organic matter (EfOM) has been reported by previous studies as responsible for membrane fouling. However, the contribution of the different components of EfOM to membrane fouling is still not well understood. In order to improve and optimize treatment processes, characterization and quantification of the organic matter are important. The characterization methods used in this study are liquid chromatography coupled with an organic detector (LC-OCD) and excitation emission matrix fluorescence spectroscopy (EEM). A bench-scale hollow fibre membrane system was used to identify the type of fouling depending on the feed water quality. Results showed no measurable dissolved organic carbon removal by the membranes for the three secondary effluents. Biopolymers and humic-like substances found in different proportions in the three effluents were partially retained by the membranes and were identified to contribute significantly to the flux decline of the low pressure membranes. The observed fouling was determined to be reversible by hydraulic backwashing for two effluents and only by chemical cleaning for the third effluent.

Investigation of the filtration characteristics of pilot-scale hollow fiber submerged MF system using cake formation model and artificial neural networks model

The submerged hollow fiber MF membrane offers a cost-effective means of removing particles and pathogens from water for drinking water production. Fouling, however, has been regarded as a major obstacle to the economical operation of membrane systems. This study focused on the investigation of the filtration characteristics of pilot-scale submerged hollow fiber membrane system using the cake formation model, based on the critical flux concept, and on the prediction of the performance of membrane filtration using artificial neural networks model (ANNs) from a long-term pilot-scale operation data.A cake formation model was applied to analyze the axial flux variations, the specific cake resistance, and the critical flux in hollow fiber membrane. The artificial neural network was applied to the simultaneous simulation of transmembrane pressure (TMP) variations in a pilot-scale membrane system.The experimental results indicated that the seasonal variations in raw water quality parameters significantly affected `the membrane permeability. The temperature of the feed water ranged from 2.1 to 26.4°C, and the turbidity ranged from 1.0 to 500 NTU, which led to completely different conditions in summer and winter. The algae concentration ranged from 0 to 47mg/m3, as did the chlorophyll-a concentration, which also led to completely different conditions in spring. A stepwise increase in the imposed flux showed that the apparent critical flux was about 60L/m2h in summer and winter. Moreover, the apparent critical flux was about 40L/m2h in spring. The cake formation model calculation was also compared with the experimental data to better understand the fouling in the hollow fiber membrane modules, and ANNs was applied to simultaneously predict the long-term membrane performance.

Analysis of local fouling in a pilot-scale submerged hollow-fiber membrane system for drinking water treatment by membrane autopsy

An analysis of local fouling in a pilot-scale submerged hollow-fiber membrane water treatment system for drinking water production is described in this paper. Membrane fouling was observed by using microscopic techniques with membrane specimen taken at different longitudinal and horizontal positions of a hollow-fiber membrane module. The resistance-in-series model was used to quantify local fouling resistances of membrane samples. Our results show that the recovery of the permeate flux of the hollow-fiber membrane located near the source of aeration was the highest after performing chemical cleaning. The irreversible fouling resistance was the largest for membrane samples taken near the open ends of the fibers, where the local pressure is expected to be highest. These axial features of irreversible fouling resistance were more pronounced at lower suspended solids concentration or higher set-point flux. However, the local aspect of reversible fouling was relatively less pronounced than the one of irreversible fouling. The results obtained from membrane autopsy were explained well by the local fouling phenomenon driven by the profile of local pressure along the fiber length and transient behavior of this profile during membrane operation. In addition, it was concluded that the individual membrane module experiencing more aeration would have a more localized pattern of membrane fouling, suggesting that the local fouling is more significant under relatively less demanding fouling conditions.

Application of low frequency transverse vibration on fouling limitation in submerged hollow fibre membranes

Abstract Dynamic membrane systems provide highly turbulent flow regimes close to the membrane surface. In this work, flux enhancement of submerged hollow fibre membrane system was achieved by imposing rotationally oscillating fluid or transverse oscillating membrane motion. The transverse vibration in the system generates the shear as well as secondary flows, contributing to fouling limitation even at low displacements (

Optimizing the sparging condition and membrane module spacing for a ZW500 submerged hollow fiber membrane system

Abstract The present study characterized the surface shear forces induced by sparging for different sparging conditions (i.e. continuous, alternating and pulse) and the membrane module configurations (i.e. spacing). The root mean square (RMS) of surface shear forces induced by gas sparging, which has been reported to be related to the extent of fouling control in membrane systems, were relatively similar for continuous, alternating and pulse sparging. Considering that pulse sparging uses approximately half of the volume of sparged gas than continuous or alternating sparging, the results suggest that pulse sparging is the best sparging approach. The RMS of surface shear forces were substantially higher for the wide module spacing than for the standard (i.e., narrow) module spacing, indicating that fouling control can likely be significantly improved by simply increasing the distance between the membrane modules.Because of the heterogeneous distribution of surface shear forces and sparged bubbles, it is ess...

Optimizing the sparging condition and membrane module spacing for a ZW500 submerged hollow fiber membrane system

Optimizing the sparging condition and membrane module spacing for a ZW500 submerged hollow fiber membrane system

Effects of operating conditions on hollow fiber membrane systems used as pretreatment for spandex wastewater reverse osmosis

Three different types of ultrafiltration (UF) membranes were investigated to treat the effluents of secondary sedimentation tank of spandex wastewater. The main parameters studied consist of the UF membrane pore size, the backwash frequency and duration time, filtration mode and the stability of the UF system. The results showed that (1) the cross-flow filtration was better in restoring K decline than the dead-end filtration; (2) the optimized backwash frequency and duration were 30 min and 2 min, respectively; (3) the modified polysulfone (PSf) UF membrane (100 kDa) was determined to be the appropriate membrane; (4) the continuous operation experiment showed that this UF system was stable.

Distribution of surface shear forces and bubble characteristics in full-scale gas sparged submerged hollow fiber membrane modules

Gas sparging is commonly used in submerged membrane systems to induce shear forces at the membrane surface, which removes the accumulated foulants. However, limited knowledge exists regarding the magnitude and distribution of these forces, especially in submerged hollow fiber membrane systems. The present study focuses on addressing this current knowledge gap by mapping the shear forces induced by gas sparging in full-scale submerged hollow fiber membrane modules. The shear forces were observed to be highly variable over time and heterogeneously distributed within the system, ranging from 0.1 to over 10Pa. The shear force measurements and the bubble counts indicated that the narrow gap between the membrane modules likely provided sufficient resistance to direct a substantial amount of the sparged bubbles to the side of the modules rather than between the membrane modules, and that regardless of the sparging flow rate, the amount of sparged bubbles that rose between the modules was constant. Increasing the sparging flow rate simply directed more of the sparged bubbles to the side of the membrane modules. As a result, the shear forces were heterogeneously distributed within the system. No correlation was observed between the shear force and bubble count or rise velocity. The distribution of sparged bubbles, the bulk liquid flow and the surface shear forces in the system were highly affected by the system geometry (e.g. module spacing, tank configuration and diffuser nozzle size).

Modeling and parametric analysis of hollow fiber membrane system for carbon capture from multicomponent flue gas

AbstractThe modeling and optimal design/operation of gas membranes for postcombustion carbon capture (PCC) is presented. A systematic methodology is presented for analysis of membrane systems considering multicomponent flue gas with CO2 as target component. Simplifying assumptions is avoided by namely multicomponent flue gas represented by CO2/N2 binary mixture or considering the co/countercurrent flow pattern of hollow‐fiber membrane system as mixed flow. Optimal regions of flue gas pressures and membrane area were found within which a technoeconomical process system design could be carried out. High selectivity was found to not necessarily have notable impact on PCC membrane performance, rather, a medium selectivity combined with medium or high permeance could be more advantageous. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Fouling indices for low pressure hollow fiber membrane performance assessment

This study evaluated the use of fouling indices to describe low pressure membrane fouling. One critical aspect of this study was the use of a bench-scale hollow fiber membrane system that imitated full-scale operation (constant flux with automatic hydraulic backwash and chemical cleaning). Fouling indices were based on a resistance-in-series model. Two different hollow fiber membrane types (membrane A and B) were tested with water from two water utilities (A and B) and three other natural sources (oligotrophic, algal bloom impacted, and wastewater impaired). The bench-scale testing included use of the same membrane as utilized at Utility B. Most fouling was reversible by hydraulic backwash and chemical cleaning. Specific flux and fouling indices for the bench-scale system were higher than those determined from full-scale data but fouling index ratios were comparable, suggesting a similar fouling nature. At similar organic loading, fouling was specific to water source and membrane type, i.e., no generalization on the impact of water source was possible. Full-scale data were compared with bench-scale data to validate the use of fouling indices. Fouling indices based on a resistance-in-series are useful tools to describe membrane performance data for both raw and pretreated water, for different water sources, and different membrane types.

Long-Term, Cytokine-Free Ex Vivo Expansion of Human Cord Blood Mononuclear Cells Using a Novel Closed-Loop 3D Dual Hollow Fibre Perfused Bioreactor

AbstractAbstract 828Human umbilical cord blood (CB) is a good source of hematopoietic stem cells (HSCs), but its use is limited by the low volume of the product and the relatively small number of HSCs. Conventional attempts at ex vivo expansion of HSCs and other hematopoietic cells have used two-dimensional (2D) tissue culture flasks or well-plates, which require feeder cells and/or various combinations of cytokines for long-term hematopoiesis. These conditions differ drastically from that provided by the natural bone marrow (BM) microenvironment wherein a complex network within the stem cell niche modulates self-renewal and pluripotency. Moreover 2D cultures have other limitations including lack of mixing, critical concentration gradients for pH, dissolved oxygen, cytokines, nutrients and metabolites, and the low number of cells that can be supported by a given surface area. Previously, we have shown that CB mononuclear cells (MNCs) can be expanded in a three dimensional (3D) static culture in cytokine-free medium for 4 weeks with a total expansion of 53-fold using polyurethane (PU) scaffolds coated with collagen type I. We hypothesized that combining these scaffolds with a perfused dual hollow fibre bioreactor (DHFB) would form a functional automatable BM biomimicry that could sustain long-term hematopoiesis and enhance the expansion of CBMNCs in a cytokine-free environment. The bioreactor includes a) a selective ceramic hollow fibre membrane system, which enables fast-flow perfusion with fresh medium for the supply of nutrients and removal of metabolites, b) a slow-flow, selectively-permeable membrane system for the supply of cytokines and the continuous harvest of mature red blood cells (RBCs) and, c) a PU scaffold rendered bioactive by collagen coating which provides a 3D in vitro culture system mimicking the natural BM microenvironment. CBMNCs were isolated using Ficoll-Paque density centrifiugation and seeded in the bioreactor at a density of 1.6×107cells/cm3. The DHFB was perfused at a flow rate of 160 ml/day in recirculation mode in order to allow for the accumulation of products. Nutrients and metabolites were monitored in the cell culture including glucose, glutamine, glutamate, lactate and ammonia and, the data used to perfuse the DHFB at optimal conditions. The hollow-fibre membranes allowed the selective mass transport of nutrients (glucose), metabolites (lactate), proteins (albumin) as well as RBCs. CBMNCs were cultured without the addition of exogenous cytokines for 3 weeks inside the DHFB, within which time cells were expanded by 300-fold, compared with 53-fold in 3D static culture correlates. Immunophenotypic analysis of extracted cells after 3 weeks showed an increase of CD71+CD45- erythroid progenitors as well as a maintained CD34+ hematopoietic progenitor cell population. Within the perfused DHFB, cells migrated into the pores of the scaffold establishing “niche-like” areas of growth identified by scanning electron microscopy, similar to those observed in static 3D culture conditions. After the 3D DHFB cultures had established, we “flexed” the system with the addition of 100ng/ml stem cell factor (SCF) and 2U/ml erythropoietin (EPO) in order to expand and mature erythrocytes and attempt selective harvesting via the closed-loop automated DHFB system. With this cocktail, mature enucleated RBCs were observed exiting the scaffold through the selectively permeable membrane, whilst other cell types and progenitors were maintained within the scaffold. This observation was confirmed by surface immunophenotype of the cells collected in the harvesting system. In conclusion, we have shown that the 3D DHFB system allowed for higher cytokine-free expansion of CBMNCs than that observed in the static 3D correlate, with evidence of directed differentiation of HSCs into erythroid progenitors in the absence of exogenous cytokines. This expansion and selective harvesting of RBCs was accomplished in a closed-loop system with monitoring and control optimisation of nutrient-waste exchange. The erythroid maturation and selective harvesting of RBCs was enhanced by the addition of SCF and EPO to the culture system. This technology enables a functional BM biomimicry and could be used as a tool to study the hematopoietic microenvironment in 3D ex vivo and for the eventual expansion of hematopoietic cell components for therapeutic use. Disclosures:No relevant conflicts of interest to declare.