Spiral-wound Membrane Elements Research Articles

Fabrication and field testing of spiral-wound membrane modules for CO2 capture from flue gas

A spiral-wound membrane module comprising face compression “O” rings for effective seal of gases was developed, including a spiral-wound membrane element, Plexiglas fiber-reinforced plastic tube, and membrane housing. The spiral-wound membrane modules demonstrated essentially no leakage. The concentration polarization phenomenon was observed at a dry feed gas flow rate of less than 1000 sccm before humidification. Hence, the performances of the spiral-wound membrane modules were evaluated using both dry feed and sweep gas flow rates each at 1000 sccm before humidification at the typical flue gas temperature of 57 °C. The feed and sweep gas pressures were at 1.5 and 1 psig, respectively. By using either a simulated flue gas or an actual flue gas, the spiral-wound membrane modules showed similar performance results with a CO2 permeance of greater than 800 GPU and a CO2/N2 selectivity of more than 140, which were essentially identical to the results obtained from the flat-sheet membrane used for the module fabrication and tested in laboratory with the simulated flue gas. The pressure drops of the modules were satisfactory, i.e., less than 1.5 psi/m. During the field test using the actual flue gas at the National Carbon Capture Center in Wilsonville, Alabama, the performances of the modules revealed some unexpected issues including the feed spacer indentations on the membrane selective layer and the leakage at glue lines. These issues were resolved by improving the spiral-wound membrane module fabrication using a smoother feed spacer and a longer glue curing time. The field test results of the modules have shown their good potential for the post-combustion CO2 capture from coal-fired power plants.

Draw channel contraction of an 8040 spiral-wound forward osmosis membrane element in pressure-assisted forward osmosis (PAFO)

Draw channel contraction of an 8040 spiral-wound forward osmosis membrane element in pressure-assisted forward osmosis (PAFO)

Effects of membrane envelope geometry on hydrodynamics inside draw channel of forward osmosis spiral wound membrane element

Effects of membrane envelope geometry on hydrodynamics inside draw channel of forward osmosis spiral wound membrane element

Microdyn-Nadir expands in spiral membranes

Mann+Hummel's water treatment business unit Microdyn-Nadir is buying Oltremare, an Italian manufacturer of spiral-wound membrane elements.

Analysis of specific energy consumption in reverse osmosis desalination processes

This paper aims to quantify the contribution of the various factors to energy consumption in reverse osmosis (RO) desalination processes and to identify those with the greatest potential for reduction. Specific energy consumption (SEC), in kWh per m3 of permeate production, is due to the retentate osmotic pressure, the resistance to fluid permeation through the membrane, the friction losses in the retentate and permeate channels of the spiral wound membrane (SWM) modules and the non-ideal operation of high pressure pumps and energy recovery devices (ERD). Taking advantage of a recently developed SWM-module performance simulator, the aforementioned individual contributions to SEC are determined for two case studies, typical of seawater and brackish water desalination processes, for steady state operation. Detailed results are obtained with SEC itemized per SWM element in a typical 7-element pressure vessel. Comparative assessment of the results is enlightening, showing that the greatest margin for the desirable SEC reduction is related to improvements of membrane permeability and efficiency of pumps and ERD. The indirect, yet significant, effect of other key design and operating process parameters is also discussed.

In-situ biofouling assessment in spacer filled channels using optical coherence tomography (OCT): 3D biofilm thickness mapping

Membrane systems for water purification can be seriously hampered by biofouling. The use of optical coherence tomography (OCT) to investigate biofilms in membrane systems has recently increased due to the ability to do the characterization in-situ and non-destructively. The OCT biofilm thickness map is presented for the first time as a tool to assess biofilm spatial distribution on a surface. The map allows the visualization and evaluation of the biofilm formation and growth in membrane filtration systems through the use of a false color scale. The biofilm development was monitored with OCT to evaluate the suitability of the proposed approach. A 3D time series analysis of biofilm development in a spacer filled channel representative of a spiral-wound membrane element was performed. The biofilm thickness map enables the time-resolved and spatial-resolved evaluation and visualization of the biofilm deposition pattern in-situ non-destructively.

Effect of initial feed and draw flowrates on performance of an 8040 spiral-wound forward osmosis membrane element

Effect of initial feed and draw flowrates on performance of an 8040 spiral-wound forward osmosis membrane element

Spatially-resolved in-situ quantification of biofouling using optical coherence tomography (OCT) and 3D image analysis in a spacer filled channel

The use of optical coherence tomography (OCT) to investigate biomass in membrane systems has increased with time. OCT is able to characterize the biomass in-situ and non-destructively. In this study, a novel approach to process three-dimensional (3D) OCT scans is proposed. The approach allows obtaining spatially-resolved detailed structural biomass information. The 3D biomass reconstruction enables analysis of the biomass only, obtained by subtracting the time zero scan to all images. A 3D time series analysis of biomass development in a spacer filled channel under representative conditions (cross flow velocity) for a spiral wound membrane element was performed. The flow cell was operated for five days with monitoring of ultrafiltration membrane performance: feed channel pressure drop and permeate flux. The biomass development in the flow cell was detected by OCT before a performance decline was observed. Feed channel pressure drop continuously increased with increasing biomass volume, while flux decline was mainly affected in the initial phase of biomass accumulation.The novel OCT imaging approach enabled the assessment of spatial biomass distribution in the flow cell, discriminating the total biomass volume between the membrane, feed spacer and glass window. Biomass accumulation was stronger on the feed spacer during the early stage of biofouling, impacting the feed channel pressure drop stronger than permeate flux.

A sequencing approach targeting the 16S rRNA gene unravels the biofilm composition of spiral-wound membranes used in the dairy industry

Few data are available concerning the composition of biofilms found at the surface of filtration membranes, which, to some extent, explains the long-term failure of numerous strategies developed to control biofouling. This preliminary study intended to design a metagenomic tool targeting the 16S rRNA gene in order to unravel a general portrait of bacterial communities found on spiral-wound membranes used in the dairy industry. A total of seven spiral-wound membrane elements (ultrafiltration, nanofiltration, or reverse osmosis) at the end of their useful lifetimes were collected from different dairy plants. Targeted analysis of the 16S rRNA genes of the metagenome extracted from the membranes revealed their bacterial diversity via high-throughput sequencing technology (Miseq, Illumina). It was found that the nature of the filtered fluid (milk, whey, water) explained 58.6 % of the variance observed between communities found on membranes. Treatments applied on dairy fluids (milk pasteurization, whey bleaching or whey ultrafiltration) induced a selective pressure that affected the diversity of bacterial communities found on membranes and the proportions of spore-former bacteria among them. This work provides the first complete bacterial portrait of the biofilm composition of spiral-wound membranes used in the dairy industry. It suggests that the nature of the filtered fluid and potentially filtration operating parameters may be important elements to consider in order to design new cleaning strategies or preventive measures targeting biofouling.

Effect of transmembrane pressure control on energy efficiency during skim milk concentration by ultrafiltration at 10 and 50°C.

The efficiency of the ultrafiltration process during skim milk concentration was studied using both dynamic and constant (465 or 672kPa) transmembrane pressure experiments at refrigerated temperature (10°C) and high temperature (50°C). The pilot-scale module was equipped with a 10-kDa polyethersulfone spiral-wound membrane element with a surface area of 2.04m2. Permeation flux, resistance-in-series model, mineral and protein rejection, and energy consumption were studied as a function of temperature and transmembrane pressure applied. Higher permeation flux values were systematically obtained at 50°C. Also, a significant temperature effect was found for calcium rejection, which was lower at 10°C compared with 50°C. Total hydraulic resistance and reversible fouling resistance were higher at 50°C than at 10°C. No change in protein rejection was observed, depending on the operating mode studied. Permeation flux, which was higher at 50°C, had lower pumping energy consumption compared with ultrafiltration at the colder temperature. Also, the low ultrafiltration temperature required a higher total energy consumption to reach the 3.6× retentate compared with ultrafiltration at 50°C. Overall, our study shows that the operating parameters and temperature can be optimized using an energy efficiency ratio.

Pilot-scale spiral wound membrane assessment for THM precursor rejection from upland waters

ABSTRACTThe outcomes of a pilot-scale study of the rejection of trihalomethanes (THMs) precursors by commercial ultrafiltration/nanofiltration (UF/NF) spiral-wound membrane elements are presented based on a single surface water source in Scotland. The study revealed the expected trend of increased flux and permeability with increasing pore size for the UF membranes; the NF membranes provided similar fluxes despite the lower nominal pore size. The dissolved organic carbon (DOC) passage decreased with decreasing molecular weight cut-off, with a less than one-third the passage recorded for the NF membranes than for the UF ones.The yield (weight % total THMs per DOC) varied between 2.5% and 8% across all membranes tested, in reasonable agreement with the literature, with the aromatic polyamide membrane providing both the lowest yield and lowest DOC passage. The proportion of the hydrophobic (HPO) fraction removed was found to increase with decreasing membrane selectivity (increasing pore size), and THM generation correlated closely (R2 = 0.98) with the permeate HPO fractional concentration.

Dominant factors controlling the efficiency of two-phase flow cleaning in spiral-wound membrane elements

Two-phase flow cleaning has been successfully applied to control fouling in spiral wound membrane elements. This study focuses on its experimental optimization using a Taguchi Design of Experiment method (L-25 orthogonal arrays) to elucidate the influence of different factors and to reveal the important one(s) affecting the cleaning efficiency of two-phase flow cleaning. All possible combinations of the factors, i.e. feed type, spacer geometry, gas/liquid ratio, and liquid velocity, each at five levels were evaluated. The main effect of each factor on the efficiency of two-phase flow cleaning was measured by determining the performance response (mean of cleaning efficiency) and by calculating the mean signal-to-noise ratio. An analysis of variance was applied to calculate the relative contribution of each factor on the efficiency of two-phase flow cleaning. The results showed that the feed type is by far the most essential factor contributing to the cleaning efficiency. The spacer geometry is ranked second, followed by the gas/liquid ratio and the liquid velocity, which both have an only very minor effect on the cleaning performance. In terms of practical application, the operator should consider first the type of foulant prior to taking a decision on whether or not two-phase flow cleaning will be effective. Once the foulant type is defined, the use of the highest gas/liquid ratio, the highest liquid velocity, and the thickest feed spacer (diamond type) are recommended to achieve maximum two-phase flow cleaning efficiency.

Membrane desalination under constant water recovery – The effect of module design parameters on system performance

The geometric design parameters of spiral-wound membrane (SWM) elements include retentate- and permeate-spacer characteristics and number of membrane envelopes (or sheet width) for constant total membrane area. A systematic assessment is made herein of the effect of these parameters (varying within realistic ranges) on the spatial distribution of all operating variables, including the permeate flux, trans-membrane pressure (TMP), retentate- and permeate-side local pressures, velocities and salt concentrations. The advanced software employed is capable of such detailed simulation of SWM module performance with no recourse to empirical parameters. The parametric study involves typical cases of desalinating (under constant recovery) brackish- and sea-water with 2000mg/L and 40,000mg/L TDS, respectively, in pressure vessels with seven 8-in. SWM-elements. The results confirm that membrane width is very important, with short sheets leading to best overall performance. The permeate-side fabric characteristics (neglected by researchers so far) significantly affect TMP and overall SWM performance, with more pronounced effect in the low-pressure modules. The effect of retentate-side spacer manifests itself mainly in the pressure drop across the module. Low-pressure module performance is comparatively more sensitive to variations of geometric parameters. The product quality (especially from high-pressure SWM modules) exhibits reduced sensitivity to significantly different design parameter-values.

Forward osmosis dialysate production using spiral-wound reverse-osmosis membrane elements: Practical limitations

We present here an experimental method of dialysate production by forward osmosis (FO) using an inexpensive reverse osmosis (RO) membrane element. This method was developed in response to the increasing need for dialysis treatment in remote and desert regions of Australia where water is precious and electricity supplies are generally unreliable.A 4040 RO membrane element was oriented for FO, using dialysate concentrate as a draw-solution and pre-treated tap-water as a feed-solution. Diluted draw-side output was collected and mixed over a range of target flow-rates. After each test the element was osmotically backwashed. Measurements were made of production time, volume and equivalent flow rates.The benefits of FO were diminished by the process׳ need for osmotic backwashing. Our system had an equivalent water recovery ranging from 65 to 75%. Its energy efficiency was 66% of its RO equivalent. Its operation was almost silent. Two 4040-size RO membrane elements would be necessary to complete a dialysis treatment. Dialysate production may be possible by this method, but its economic and conservation benefits appear to be modest.

Hydrogel-coated feed spacers in two-phase flow cleaning in spiral wound membrane elements: A novel platform for eco-friendly biofouling mitigation

Biofouling is still a major challenge in the application of nanofiltration and reverse osmosis membranes. Here we present a platform approach for environmentally friendly biofouling control using a combination of a hydrogel-coated feed spacer and two-phase flow cleaning. Neutral (polyHEMA-co-PEG10MA), cationic (polyDMAEMA) and anionic (polySPMA) hydrogels have been successfully grafted onto polypropylene (PP) feed spacers via plasma-mediated UV-polymerization. These coatings maintained their chemical stability after 7 days incubation in neutral (pH 7), acidic (pH 5) and basic (pH 9) environments. Anti-biofouling properties of these coatings were evaluated by Escherichia coli attachment assay and nanofiltration experiments at a TMP of 600 kPag using tap water with additional nutrients as feed and by using optical coherence tomography. Especially the anionic polySPMA-coated PP feed spacer shows reduced attachment of E. coli and biofouling in the spacer-filled narrow channels resulting in delayed biofilm growth. Employing this highly hydrophilic coating during removal of biofouling by two-phase flow cleaning also showed enhanced cleaning efficiency, feed channel pressure drop and flux recoveries. The strong hydrophilic nature and the presence of negative charge on polySPMA are most probably responsible for the improved antifouling behavior. A combination of polySPMA-coated PP feed spacers and two-phase flow cleaning therefore is promising and an environmentally friendly approach to control biofouling in NF/RO systems employing spiral-wound membrane modules.

Operation and simulation of pilot-scale forward osmosis desalination with ammonium bicarbonate

A pilot-scale forward osmosis desalination system is developed and demonstrated employing ammonium bicarbonate as its draw solute. The system consists of three stages: (1) water permeation through the membrane, (2) draw solute and water separation, and (3) draw solute recovery. In the membrane process, multiple spiral wound membrane elements are connected to investigate the water recovery change according to the membrane area. The draw solution diluted by water permeated through the membrane from the salt water enters a packed column where ammonium bicarbonate is decomposed into ammonia and carbon dioxide. The separation efficiency and energy consumption of the separation column are measured for 120kg/h fresh water production. Lastly, the draw solutes are then recovered back into the system by absorption with the diluted ammonium bicarbonate solution. The operational results are compared to those from simulation. The results of this study will contribute to facilitating the technical and economical evaluation of forward osmosis desalination systems.

Monitoring the membrane scaling propensity of retentate in reverse osmosis desalination plants

Scaling appears first in the tail spiral wound membrane (SWM) elements of desalination plants due to increased salt concentration in the retentate; in particular, membrane scaling starts locally when supersaturation of sparingly soluble salts (commonly CaCO3 and CaSO4) is attained. Reliable determination of the onset of membrane scaling in the tail elements (as a function of the local retentate physico-chemical properties) provides a threshold condition serving a dual purpose; i.e., it imposes essentially an upper limit to the degree of permeate recovery, and guides the selection of an appropriate anti-scaling program involving additives. Judicious use of the latter is important for reduction of desalination cost and environmental impact. The current practices for estimating incipient scaling within the spacer filled reverse osmosis (RO) membrane elements involve a great deal of uncertainty. In this study, slightly supersaturated in CaCO3 brackish waters were desalinated in a test section comprising a narrow gap spacer filled channel simulating local (constant flux) conditions in SWM modules. Detailed data on incipient membrane scaling were obtained leading to the following main conclusions: (a) minute quantities of very small particles, ever present in RO plants, apparently promote heterogeneous nucleation; moreover, under the conditions tested, induction period for membrane scaling is practically nonexistent. (b) the initial scale deposit rates measured by special techniques (but undetectable with common bulk flow measurements) are substantial, and if not mitigated would be detrimental to SWM performance over a relatively short operating time period. (c) accurate determination of supersaturation ratio at the membrane surface Sw can be a reliable criterion for the onset of scaling, instead of currently used indices (e.g. Langelier Saturation Index) or practical type recommendations; a reliable method has been employed to determine Sw under local retentate conditions. Based on these results, a novel system was developed for monitoring the scaling propensity of retentate, which involves combination of a limited number of measurements in key locations of a RO plant, reliable algorithms for local equilibria and supersaturation (Sw) calculations, and a modern wireless electronic system for plant wide monitoring.

Forward osmosis dialysate production using spiral-wound reverse-osmosis membrane elements

Presented here is an analysis of a method by which a spiral-wound reverse osmosis (RO) membrane element may be used in forward osmosis (FO) mode to produce dialysate fluid for medical treatment. In this method, dialysate is produced from the draw-side of an FO process by carefully controlling the output concentration, managing the accumulation of salt in the closed, feed-side membrane envelope and using osmotic backwashing to recover the membrane.The analysis shows that a high-quality, spiral-wound, polyamide 4040 RO membrane element may be used to produce un-buffered dialysate when supplied with brackish groundwater and dialysate concentrate. Production is possible for a short period before the membrane needs to be osmotically backwashed to remove accumulated salt. By alternating between production and backwashing cycles, a pair of high-quality 4040 elements may produce dialysate at a rate high enough to enable continuous haemodialysis treatment.The low-cost, compact nature of standard RO elements makes them suitable for water and energy-efficient FO applications. The method proposed here exploits the features of standard RO elements to enable their application in Australian desert regions, where water supplies are slightly brackish and where rates of kidney failure and dialysis treatment are relatively high.

Incipient membrane scaling by calcium sulfate during desalination in narrow spacer-filled channels

New insights were gained by studying in detail (using Scanning Electrode Microscopy—SEM) incipient calcium-sulfate scaling of desalination membranes under realistic conditions; i.e. low supersaturation ratio S, once-through flow in narrow spacer-filled channels, with permeate-flux and cross-flow velocity levels encountered at the tail spiral-wound membrane (SWM) elements, where supersaturation first appears. Moreover, the feed-fluid was fully characterized, including its small-particle content. SEM images from desalination membranes and filters retaining small particles from feed- and retentate-samples were statistically analyzed. For 90min tests, elongated gypsum crystals are sparsely distributed throughout the membrane, at the smallest supersaturation; at elevated S, clusters of needles/rods and platelets develop with increasing membrane-surface density. Similarly, the initial scale deposition rate [mg/(m2min)] and membrane-surface coverage tend to increase rather sharply with increasing S. The data provide no evidence of induction period for membrane scaling, as also recently observed in studying incipient CaCO3 scaling. Additionally, there is strong indication that incipient CaSO4 scaling is due to growth of membrane surface particles (from nuclei developing right on the surface and/or transported to the membrane) and not due to deposition of crystals developing in the bulk. The implications of the new results are discussed and related R&D needs are outlined.

The effect of spiral wound membrane element design characteristics on its performance in steady state desalination — A parametric study

The spiral-wound membrane (SWM) element design variables include retentate- and permeate-spacer characteristics and number of membrane envelopes (or sheet width) for constant total area, in addition to membrane surface properties. The effect of these parameters (varying within realistic ranges) on the operating variables, comprising two-dimensional distribution of permeate flux, trans-membrane pressure (TMP), retentate- and permeate-side pressures and velocities, is systematically assessed. Advanced software is employed, capable of simulating SWM desalination performance with no recourse to empirical parameters. The parametric study involves typical cases of desalinating brackish and sea-water with 2000mg/L and 40,000mg/L TDS, respectively, in pressure vessels with seven 8-inch SWM-elements. The results show that low-pressure desalination modules are most sensitive to variations of geometric parameters. The effect of permeate-side fabric is significant, directly affecting TMP and module productivity. In both low- and high-pressure desalination, the effect of retentate-side spacer manifests itself mainly in the pressure drop across the element. The results confirm that the membrane width is very important, with short sheets exhibiting the best overall performance. Noteworthy is the insensitivity of high-pressure SWM-module productivity to significantly different design parameter-values, including envelope width. These results are helpful in guiding SWM element optimization and in setting priorities for related R&D work.