Hollow fiber ultrafiltration: The concept of partial backwashing

Forward osmosis (FO) is a membrane process that occurs when solutions of different osmotic pressures are separated by a membrane which is selectively permeable to water. It is a process that drives water permeation across the membrane spontaneously even in the absence of hydraulic pressure difference across the membrane. FO has attracted lots of attention over the last decade and has been explored as a potential alternative to desalination, wastewater treatment and liquid food processing. Significant progress has been made in the development of high-performance FO membranes with high water flux and low reverse solute flux, particularly cellulosic membranes, thin-film composite (TFC) membranes and polyelectrolyte-based membranes. Yet, a few major challenges continue to hamper the widespread implementation of the process in the industry, mainly internal concentration polarization, reverse solute diffusion, membrane fouling, mechanical durability and draw solution regeneration. Most of these challenges are associated with membrane characteristics, which has significantly limited the efficiency of the FO process. To address these challenges, firstly, hollow fiber ultrafiltration membranes were fabricated from polyethersulfone (PES) via a non-solvent induced phase separation (NIPS) process and were used as substrates to prepare inner-selective TFC hollow fiber membranes via an interfacial polymerization (IP) process. The effect of the hollow fiber substrate fabrication conditions on the properties of the substrate and TFC membranes were briefly investigated. The FO performance of the TFC membranes were characterized by using 0.5 M NaCl and DI water as the draw and feed solutions. when the membrane was operated in the active layer-facing-feed solution (AL-FS) and active layer-facing-draw solution (AL-DS) configurations, water flux as high as 41.2 L/m2/h and 74.9 L/m2/h were achieved, while specific reverse solute flux were 0.11 g/L and 0.10 g/L, respectively. Subsequently, a novel double-skinned hollow fiber TFC FO membrane has been successfully fabricated. The FO membrane consisted of a one-step dual-layer substrate and a thin inner selective layer formed via the IP process. The substrate comprises a dense ultrafiltration (UF) outer layer and a relatively porous UF inner layer, both of which were constructed from PES by using a dual-layer co-extrusion technique. The fouling resistance of the double-skinned hollow fiber membrane was evaluated under various testing conditions to verify the viability of double-skinned hollow fiber membranes as a solution to membrane fouling in the FO process. Compared to the commercial and reported double-skinned FO membranes, the FO membrane developed in this thesis exhibited a higher permeate flux with humic acid solution as a feed solution. Furthermore, the double-skinned FO membrane was applied in concentrating activated sludge using 0.5 M NaCl as a draw solution. A permeate flux at 5.4 L/m2/h was achieved after 5-hour operation, which was higher than, or comparable to, those of the reported FO membranes. Membrane autopsies and foulant analysis suggested that the dense UF skin layer helped to reject larger-sized organic foulants (> 300 Da), which shed light on the importance of fabrication features and promising application of the double-skinned hollow fiber TFC FO membrane in sludge concentration. On the other hand, a series of characterization revealed that TFC hollow fiber membranes may experience significant compaction during the FO process despite the lack of applied pressure. Three TFC hollow fiber membranes were fabricated with varied water permeability to study the effect of the osmotic pressure on the TFC membranes. The TFC membranes were continuously tested in FO experiments for 24 h using DI water as feed and varied concentration of NaCl solutions as draw solutions, and their performances were evaluated again using fresh feed solutions. At the end of the FO experiments, all TFC membranes experienced water and salt flux decline to different extents. Visible changes in the cross-sectional morphology and surface topography of the TFC membranes were observed. These observations suggested that the occurrence of membrane compaction is strongly associated with the characteristics of the hollow fiber substrates that were used to prepare the TFC membranes and may be attributed to “negative pressure” build-up within the support layer of the TFC membranes.

In order to ensure long-term sustainability of the reservoir, the gas industry in Qatar is faced with the challenge of reducing the volume of produced and process water (PPW) sent to disposal wells by 50% [1-3]. Recently, Qatargas initiated a project to recycle process water and thus, reduce disposal volumes using commercial advanced water treatment technologies [4]. One emerging technology, “osmotic concentration” (OC) has been identified that offers a low-energy alternative to conventional thermal or membrane volume reduction methods. Osmotic concentration is a membrane filtration process that mimics first step in a forward osmosis (FO) system. It requires a high salinity draw solution (DS) which passes on one side of a semi-permeable FO membrane while the feed passes on the other side. Water from the feed is drawn through the membrane, via natural osmosis, reducing the feed volume and increasing the volume of the draw solution. This paper summarizes the results of bench-scale volume reduction tests wit...

This study has demonstrated the application of tight ultrafiltration (UF) membranes for effective removal of textile dyes from water at a low pressure. Novel UF hollow fiber membranes with well-defined nanopores and surface charges were developed via a single-step spinning process without any post-treatment. The newly developed tight UF hollow fibers not only possess a small mean pore diameter of 1.0-1.3 nm with a molecular weight cutoff (MWCO) of 1000-2000 Da but also have a high pure water permeability (PWP) of 82.5-117.6 L m-2 h-1 bar-1. Through the synergistic effects of size exclusion and charge repulsion, the novel UF hollow fibers can effectively remove various dyes with impressive rejections of 93.2-99.9% at 1 bar. At the same time, more than 92% of inorganic salts (i.e., NaCl and Na2SO4) would permeate through the fibers, reducing the detrimental effects of concentration polarization and providing an attracted avenue for salts reuse. The tight UF hollow fibers also exhibit robust performance in a continuous operation of 170 h or at a high feed recovery of 90%. The fouled fibers can be easily regenerated by backwash of water with a flux recovery of larger than 92%. The newly developed tight UF hollow fiber membranes display huge potential for treating textile wastewater and other impaired effluents because of their great separation performance and simple fabrication process.

Sedimentation and drying dissipative structural patterns formed in the course of drying colloidal silica spheres (1.2 μm in diameter) in aqueous suspension have been studied in a glass dish and a polystyrene dish. The broad ring patterns are formed within a short time in suspension state by the convection flow of water and colloidal spheres. The broad ring patterns are not formed when a dish is covered with a cap, which demonstrates the important role of the convectional flow of silica spheres and water accompanied with the evaporation of water on the air-suspension interface. The sedimentary spheres always move by the convectional flow of water, and the broad ring patterns became sharp with time. Broad ring and microscopic fine structures are formed in the solidification processes on the bases of the convectional and sedimentation patterns. Drying patterns of the colloidal suspensions containing sodium chloride are star-like ones, which strongly supports the synchronous cooperative interactions between the salt and colloidal spheres.

Sedimentation and drying dissipative patterns formed in the course of drying green tea (Ocha) have been studied in tea cup (Ochawan), glass dish, polystyrene dish, and watch glass. The broad-ring patterns are formed within several tens of minutes in suspension state by the convectional flow of water and colloidal particles of green tea (7 μm in mean size and 5 μm in its dispersion from the mean size). Formation of the broad-ring patterns is retarded when a tea cup is covered with a watch glass, which demonstrates the important role of the convectional flow of tea particles and water induced by the evaporation of water at the air-suspension interface under the gravity. The sedimentary particles are suspended above the substrate plate and always move by the convectional flow of water. The broad-ring patterns become sharp just before the solidification occurs. The broad rings are formed even in an inclined glass dish, though the rings are transformed slightly, which demonstrates the strong convectional flow of the particles. The drying broad rings and the microscopic fine structures are formed in the solidification processes on the bases of the convectional and sedimentation patterns in suspension state.

The organic fouling characteristics of hollow fiber ultrafiltration (HFUF) and multibore ultrafiltration (MBUF) membranes from long-term ultrafiltration (UF) membrane systems were systemically investigated in this study. The objective was to obtain insights into the fouling behavior of dissolved organic matter (DOM) in a pilot-scale ultra-high-recovery membrane filtration system (p-UHMS) used for surface water treatment. The pilot system consisted of a series of two different UF membranes (1st stage: polyvinylidene fluoride (PVDF) HFUF and 2nd stage: polyethersulfone (PES) MBUF). It was designed to feed the HFUF concentrate to the MBUF membranes to achieve ≥99.5 % total water recovery for surface water treatment, as these advances might enhance the production efficiencies of drinking water. The experimental results confirmed that hydrophobic DOM controlled the formation of HFUF membrane organic fouling, whereas hydrophilic DOM, including polysaccharide-like and protein-like matter, promoted MBUF membrane fouling. These opposing trends were attributed to the hydrophilic characteristics of the MBUF membrane surfaces (contact angle: PVDF = 90–130° and PES ≤ 80°), which reduced the hydrophobic interactions between the UF membrane surfaces and foulants. The performance declines of the MBUF membrane due to fouling layer formation was considerably severer than those of the HFUF membrane, decreasing total permeate water in the p-UHMS. Moreover, the quantity of the desorbed MBUF membrane foulants via 0.1 N NaOH was roughly 7.2 times larger than that of the desorbed HFUF membrane foulants through 0.1 N NaOH, indicating that alkaline-based cleaning agent could much more efficiently recover the performance of the fouled MBUF membranes. Hence, adequate cleaning strategies using alkaline-based agent for the MBUF membrane appeared to be essential for preventing the performance deterioration of the p-UHMS.

Decrease in soil organic matter has emerged as a major concern in blackgram (Vigna mungo L) productivity highlighting the need of sustainable organic nutrient management practices. Organics in the form of humic acid and compost are playing the important role to improve soil fertility as well productivity of the crop. These treatments included: two controls, sowing of dry seeds and water-primed seeds, seed priming treatments using 0.5%, 1%, and 2% humic acid (HA) solutions, soil application of 1 kg ha−1 humic acid, 2 kg ha−1 humic acid, 1 kg ha−1 humic acid + 10 t compost, and 2 kg ha−1 humic acid + 10 t compost and foliar application using 0.01%, 0.05%, and 0.1% humic acid solutions at 25 days after sowing. The application of humic acid and compost to the soil had a significant effect on the pod count per square meter, other yield parameters such as seeds per pod and pod length exhibited comparable statistical results in both the years of the study. However, seeds/pod in 2019 varied significantly due to treatment effects. The maximum seed yield and seed protein content (1186.9 kg/ha & 1209.5 kg/ha, and 24.77% & 25.02%, respectively) were obtained from T9 (application of humic acid in soil @ 2 kg/ha in addition to compost @10 t/ha) followed by T8 (application of humic acid soil @ 1 kg/ha in addition to compost @ 10 t/ha). Data recorded further revealed crop performance was better with soil and foliar application of humic acid than seed priming with humic acid solution.

Fouling evaluation of PES/ZnO mixed matrix hollow fiber membrane

The effect of hollow fiber module positions (horizontal and vertical) on separation performance for PVA solution by using polyethersulfone (PES) hollow fiber ultrafiltration (UF) membrane with the molecular weight cut-off (MWCO) 30 000 has been discussed. Experimental results illustrated that the suitable operation conditions for PVA solution were as follows: trans-membrane pressure 2.1 bar, solution temperature 75 °C and feed velocity 0.32 m/s. Under these suitable operation conditions, the permeate flux is from 36.8 L/(m2·h· bar) to 42.9 L/(m2· h· bar) for the horizontal module and from 39.8 L/(m2· h· bar) to 66.6 L/(m2· h· bar) for the vertical module. Besides, the separation performance of PES hollow fiber UF membrane was better by using vertical hollow fiber module than by using horizontal hollow fiber module. When the trans-membrane pressure increased from 1 bar to 2.1 bar, solution temperature from 50 °C to 75 °C, feed solution velocity from 0.16 m/s to 0.32 m/s, the PVA rejection would increase from 95.8% to 99.7%, 95.4% to 98.6%, 95.8% to 99.2% for horizontal module respectively, and from 98.8% to 99.8%, 98.6% to 99.4%, 98.5% to 99.4% for vertical module respectively. Therefore, PVA rejection in PES hollow fiber UF process was more than 98.5% for vertical module, and it is suitable for PVA recovery from wastewater.

Preparation and characterization of thermally stable copoly(phthalazinone biphenyl ether sulfone) hollow fiber ultrafiltration membranes

Investigation of shear stress effect within a spinneret on flux, separation and thermomechanical properties of hollow fiber ultrafiltration membranes

This study investigated the separation of lead, mercury and arsenic ions from feed solution, i.e., produced water and synthetic water across hollow fiber supported liquid membrane (HFSLM). The influences of types of extractants (D2EHPA, TOA, Aliquat 336, Bromo-PADAP, Cyanex 471 and Cyanex 923), concentration of the extractants, types of stripping solutions (distilled water, HNO3, H2SO4, HCl, NaOH and thiourea), concentration of the stripping solutions, concentration of H2SO4 in feed solution, flow patterns of feed and stripping solutions, types of lead complexes in the feed solution, types of extractans and stripping solutions in the HFSLM series, operating time, and flow rates of feed and stripping solutions were investigated. For the separation of mercury and arsenic ions from produced water, the superior performance in the extraction of mercury compared with arsenic was observed. Remarkably, the synergistic extraction of arsenic was discovered by using the mixture of Aliquat 336 and Cyanex 471 at the synergistic coefficient of 2.8. Thiourea of 0.1 M was found to be the suitable stripping solution. The concentrations of discharged mercury and arsenic ions complied with the regulatory discharge standards by using the mixture of 0.22 M Aliquat 336 and 0.06 M Cyanex 471 with 0.2 M H2SO4 in feed solution at 1 and 3 cycle separations, respectively. In the case of the separation of Pb(II) and Hg(II) from synthetic water, it was found that by using a double-module HFSLM in series could extract lead and mercury ions below their regulatory discharge standards in 80 min. The concentrations of lead and mercury ions in the stripping solutions were higher than those in the inlet feed solution of about 2.7 and 1.2 times. The optimum conditions were achieved by using 0.03 M D2EHPA as the extractant and 0.9 M HCl as the stripping solution in the first module, and 0.06 M Aliquat 336 as the extractant and 0.1 M thiourea as the stripping solution in the second module. A single-pass flow pattern of feed solution and circulating flow pattern of the stripping solution of 100 mL/min were found to be the most suitable. In addition, a mathematical model to predict the separation of lead and mercury ions was developed by considering the material balance concept in terms of convection and accumulation of metal ions, and the reactions at the liquid-membrane interfaces. Consequently, the concentrations of lead and mercury ions in feed and stripping solutions predicted by the model agreed well with the experimental results. It indicated that the rates of lead and mercury ions transport from feed solution to the stripping solution corresponded to the convection and accumulation of lead and mercury ions and the reactions at the liquid-membrane interfaces.

BACKGROUND AND AIMS When polymethyl methacrylate (PMMA) membranes are used in renal replacement therapy, inflammatory cytokines and other substances are removed by adsorption. However, these filters are also prone to clogging and the filter lifetimes are likely to be short. In the present study, we investigated the effects of the hollow fiber inner diameter and membrane area of PMMA membranes on the filter lifetime and protein removal performance using an in vitro continuous hemofiltration (CHF) experimental model with porcine blood. METHOD Three filters with different hollow fiber inner diameters and membrane areas were used: CH-1.0N (membrane area, 1.0 m2; hollow fiber inner diameter, 200 µm), CH-1.0W (prototype: 1.0 m2; 240 µm), and CH-1.8W (1.8 m2; 240 µm). Blood samples from one pig were divided into three portions, and in vitro CHF experiments for each filter were performed at QB = 100 mL/min and QS = QF = 10 mL/min. The pressure changes, total protein concentration in the blood, and total protein amount in the filtrate were measured during the experiments. From the results of the pressure changes, the time for the TMP to reach 200 mmHg (corresponding to the time when the membrane pores were clogged) and the time for the pressure drop through the filter to reach 200 mmHg (corresponding to the time when the hollow fibers were clogged) were calculated as the filter lifetime for comparative evaluation. RESULTS The time for the TMP to reach 200 mmHg was significantly longer with CH-1.8W than that with CH-1.0N or CH-1.0W (Friedman test, P < .05, n = 15). The time for the pressure drop through the filter to reach 200 mmHg was significantly longer with CH-1.8W than that with CH-1.0N or CH-1.0W (Friedman test, P < 0.05, n = 15). The results suggest that an increased membrane surface area is an essential factor for extending the filter lifetime. The total protein adsorption was significantly higher for the CH-1.0W and CH-1.8W filters than for the CH-1.0N filter (two-way ANOVA and post hoc Tukey test, P < 0.01, n = 15). Thus, the membranes with larger hollow fiber inner diameters (CH-1.8W and CH-1.0W) adsorbed more protein. CONCLUSION A larger membrane area contributes to a longer filter lifetime, whereas increase in the hollow fiber inner diameter does not. On the other hand, the protein removal performance, especially the adsorption performance, was higher for membranes with larger hollow fiber inner diameters.

To investigate diffusion in mammalian cell culture by gel entrapment within hollow fibers. Freshly isolated rat hepatocytes or human oral epidermoid carcinoma (KB) cells were entrapped in type I collagen solutions and statically cultured inside microporous and ultrafiltration hollow fibers. During the culture time collagen gel contraction, cell viability and specific function were assessed. Effective diffusion coefficients of glucose in cell-matrix gels were determined by lag time analysis in a diffusion cell. Significant gel contractions occurred in the collagen gels by entrapment of either viable hepatocytes or KB cells. And the gel contraction caused a significant reduction on effective diffusion coefficient of glucose. The cell viability assay of both hepatocytes and KB cells statically cultured in hollow fibers by collagen entrapment further confirmed the existence of the inhibited mass transfer by diffusion. Urea was secreted about 50% more by hepatocytes entrapped in hollow fibers with pore size of 0.1 mum than that in hollow fibers with MWCO of 100 ku. Cell-matrix gel and membrane pore size are the two factors relevant to the limited mass transfer by diffusion in such gel entrapment of mammalian cell culture.

Cellulose acetate (CA) ultrafiltration hollow fibers were prepared via the dry–wet spinning technique. In the spinning process, the coagulant temperature was varied, and hence the on-line draw ratio was affected. The results revealed that the maximal draw ratio increased with the increase of coagulant temperature up to 55 ○C and then leveled off. The inner diameters, outer diameters and thickness of the hollow fiber decreased with the increase of the draw ratio. The tensile properties of the resulting hollow fibers were measured, and the breaking tensile stress increased with the increase of draw ratio. When the coagulant temperature was increased from 25 to 70 ○C, the porosity increased, the pore size was slightly enlarged in the outer skin, the hydraulic permeability increased, and the percentage of retention R decreased. In summary, by increasing the coagulant temperature, the maximal draw ratio can be increased, and hence the mass transfer properties and the other properties of drawn CA hollow fiber can be varied.