湿式催化氧化/膜过滤组合工艺膜过滤机理

采用湿式催化氧化/膜过滤组合工艺,以Mo-Zn-Al-O粉末作为催化剂降解阳离子红GTL模拟染料废水,探讨在膜过滤过程中平均孔径为0.1 μm的微滤和0.022 μm的超滤聚偏氟乙烯(PVDF)中空纤维膜的过滤机理。实验结果表明,两种膜过滤组合工艺对染料的降解效果均优于单独湿式催化氧化,0.01 MPa恒压条件下运行120 min后微滤和超滤的膜通量分别衰减了26.63%和16.48%,其原因是粉末催化剂可在微滤膜孔内部沉积形成中间阻塞过滤,后在表面形成滤饼层;而在超滤膜表面仅形成滤饼层。通过实验结果对膜阻力进行计算,可知在相同反应过程后微滤膜产生的不可逆阻力大于超滤膜。在不同反应条件下,催化剂的沉积量与膜阻力呈现线性相关。     

Design and fabrication of whisker hybrid ceramic membranes with narrow pore size distribution and high permeability via co-sintering process

Ceramic microfiltration membranes (MF) with narrow pore size distribution and high permeability are widely used for the preparation of ceramic ultrafiltration membranes (UF) and in wastewater treatment. In this work, a whisker hybrid ceramic membrane (WHCM) consisting of a whisker layer and an alumina layer was designed to achieve high permeability and narrow pore size distribution based on the relative resistance obtained using the Hagen-Poiseuille and Darcy equations. The whisker layer was designed to prevent the penetration of alumina particles into the support and ensure a high porosity of the membrane, while the alumina layer provided a smooth surface and narrow pore size distribution. Mass transfer resistance is critical to reduce the effect of the membrane layers. It was found that the resistance of the WHCM depended largely on the alumina layer. The effect of the support and whisker layer on the resistance of the WHCM was negligible. This was consistent with theoretical calculations. The WHCM was co-sintered at 1000?°C, which resulted in a high permeability of ~?645?L?m^?1 h^?1 ;bar^?1 and a narrow pore size distribution of ~?100?nm. Co-sintering was carried out on a macroporous ceramic support (just needed one sintering process), which greatly reduced the preparation cost and time. The WHCM (as the sub-layer) also showed a great potential to be used for the fabrication of ceramic UF membranes with high repeatability. Hence, this study provides an efficient approach for the fabrication of advanced ceramic MF membranes on macroporous supports, allowing for rapid prototyping with scale-up capability.     

Influence of polydopamine deposition conditions on pure water flux and foulant adhesion resistance of reverse osmosis, ultrafiltration, and microfiltration membranes

The influence of polydopamine (PDOPA) deposition and poly(ethylene glycol) (PEG) grafting on pure water flux and bovine serum albumin (BSA) adhesion of two polysulfone ultrafiltration (UF) membranes, a poly(vinylidene fluoride) microfiltration (MF) membrane, and a polyamide reverse osmosis (RO) membrane is reported. When modified with PDOPA, all membranes exhibited a systematic reduction in protein adhesion. For example, 90 min of PDOPA deposition led to at least 96% reduction in BSA adhesion to these membranes at neutral pH. BSA adhesion was further reduced by subsequent PEG grafting to PDOPA (PDOPA-g-PEG). The membranes’ pure water flux values (i.e., with no foulants present) were influenced to different extents by PDOPA and PDOPA-g-PEG modifications. In the porous membranes (i.e., the UF and MF membranes), the pure water flux reduction due to these modifications correlated with membrane pore size, with the smallest flux reductions observed in the MF membrane (e.g., <1% flux reduction for all PDOPA modification times considered), which have the largest pores, and the largest flux reductions occurring in UF membranes (e.g., a 40% flux reduction after 90 min of PDOPA deposition), which have pore sizes on the order of the PDOPA deposition thickness. The RO membranes, which are essentially non-porous, exhibited a flux reduction of 25% after 90 min of PDOPA deposition.     

混凝耦合多孔陶瓷膜净化河水简

Membrane filtration technology combined with coagulation is widely used to purify river water. In this study, micro filtration （MF） and ultrafiltration （UF） ceramic membranes were combined with coagulation to treat local river water located at Xinghua, Jiangsu province, China. The operation parameters, fouling mechanism and pilot-scale tests were investigated. The results show that the pore size of membrane has small effect on the pseudo-steady flux for dead-end filtration, and the increase of flux in MF process is more than that in UF process for cross-flow filtration with the same increase of cross-flow velocity. The membrane pore size has little influence on the water quality. The analysis on membrane fouling mechanism shows that the cake filtrationhas significant in fluence on the pseudo-steady flux and water quality for the membrane with pore size of 50, 200 and 500 nm. For the membrane with pore size of 200 nm and backwashing employed in our pilot study, a constant flux of 150 L-m^-2-h^-1 was reached during stable operation, with the removal efficiency of turbidity, total organic carbon （TOC） and UV254 higher than 99%, 45% and 48%, respectively. The study demonstrates that coagulation-porous ceramic membrane hybrid process is a reliable method for river water purification.     

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

The 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.     

In‐line Flocculation‐Submersed MF/UF Membrane Hybrid System in Tertiary Wastewater Treatment

Abstract

Coagulation/flocculation pre‐treatment of feeds can successfully mitigate the drawbacks of membrane micro‐ and ultra filtration processes: fouling and limited ability to remove organic pollutants. Laboratory experiments conducted with a synthetic wastewater (representing biologically treated secondary effluent) using 0.1 µm pore size hollow fiber membrane showed that simple in‐line flocculation pre‐treatment with inorganic coagulants dramatically reduced membrane fouling rates. The hybrid system also ensured over 70% organic matter removal in terms of dissolved organic carbon (DOC). In the experiments in in‐line flocculation outperformed clarification pre‐treatment at optimum coagulant dosages. Differences in floc characteristics and elevated suspended solids concentrations in the membrane tank may explain this finding, but the exact causes were not investigated in this study. The beneficial effects of in‐line flocculation pre‐treatment to MF/UF separation were also confirmed in the treatment of septic tank effluent in a membrane bioreactor (MBR). The fouling rate of the 0.4 µm pore size (flat‐sheet) membrane was substantially reduced with 10–100 mg L^?1 ferric chloride coagulant doses, and total dissolved chemical oxygen demand (DCOD) removal also increased from 66% up to 93%. These findings are consistent with the results of other experimental studies and show that pre‐treatment controls submersed MF/UF filtration performance.     

Nonuniform deposition of particles inside the pores of a semipermeable membrane

Macroscopic equations of the theory of filtration through granular beds are used to consider the spatial nonuniformity of particle deposition on pore walls during the standard blocking of the pores of ultrafiltration (UF) and microfiltration (MF) membranes. It is shown that the thickness of the layer of particles deposited inside the pore is characterized by a high degree of nonuniformity, which considerably affects the values of membrane permeate flux and selectivity. The effect of pore diameter, pore length, transmembrane pressure, and the coefficient of particle deposition onto the inner pore surface on the performance of standard blocking is studied. A dimensionless number representing the combination of the above parameters is proposed. The number can be used for optimizing the choice of membranes and process parameters for the UF and MF processes using standard blocking.     

Purification and Concentration of Caustic Mercerization Wastewater by Membrane Processes and Evaporation for Reuse

A membrane-based treatment strategy was developed for purifying the highly alkaline textile mercerization wastewater. 0.2-μm MF and 100 kDa UF membranes were evaluated as pretreatment alternatives before 10 kDa UF and 200 Da NF membranes. Turbidity was almost totally removed by both pretreatment options, while UF (100 kDa) showed higher COD retention than MF. In total recycle mode of filtration, fouling of both UF and MF membranes were 80% reversible by physical and almost totally reversible (≥ 97%) by chemical cleaning. In the second stage filtrations applied to the pretreated wastewater samples, NF could yield high (97-98%) COD retentions and low permeate COD concentrations (≤ 22 mg/L), while 10 kDa UF could only reduce the COD concentration to 150 mg/L. While no NaOH was lost in the MF+UF process, the use of NF as second stage resulted in 12-17% NaOH retention. The permeate flux in all second stage processes were stable, implying that the majority of the feed components that would cause fouling had been removed in the pretreatment stages. Permeate of the MF+NF sequence was concentrated by evaporation with no foaming problems, showing that the hybrid process can be applied to recycle a purified and concentrated caustic stream to the mercerization process.     

Manufacture and characterization of ultra and microfiltration ceramic membranes by isostatic pressing

This paper describes the manufacture of tubular UF and MF porous and supported ceramic membranes to oil/water emulsions demulsification. For such a purpose, a rigorous control was realized over the distribution and size of pores. Suspensions at 30 vol.% of solids (zirconia or alumina powder and sucrose) and 70 vol.% of liquids (isopropyl alcohol and PVB) were prepared in a jar mill varying the milling time of the sucrose particles, according to the pores size expected. The membranes were prepared by isostatic pressing method and structurally characterized by SEM, porosimetry by mercury intrusion and measurements of weight by immersion. The morphological characterization of the membranes identified the formation of porous zirconia and alumina membranes and supported membranes. The results of porosimetry analysis by mercury intrusion presented an average pore size of 1.8 μm for the microfiltration porous membranes and for the ultrafiltration supported membranes, pores with average size of 0.01-0.03 μm in the top-layer and 1.8 μm in the support. By means of the manufacture method applied, it was possible to produce ultra and microfiltration membranes with high potential to be applied to the separation of oil/water emulsions.     

Irreversible Fouling in MF/UF Membranes Caused by Natural Organic Matters (NOMs) Isolated from Different Origins

Abstract

For more efficient use of membrane technology in water treatment, it is essential to understand more about the fouling that requires chemical cleaning to be eliminated (i.e., irreversible fouling). In this study, five different MF/UF membranes and four types of organic matter collected from different origins were examined in terms of the degree of irreversible membrane fouling. Experimental results demonstrated that the extent of irreversible fouling differed significantly depending on the properties of both the membrane and organic matter. Among the tested membranes, UF membranes made of polyacrylonitrile (PAN) exhibited the best performance in terms of prevention of irreversible fouling. In contrast, MF membranes, especially one made of polyvinylidenefluoride (PVDF), suffered significant irreversible fouling. Conventional methods for characterization of organic matter such as specific ultraviolet absorption (SUVA), XAD fractionation, and excitation‐emission matrix (EEM) were found to be inadequate for prediction of the degree of irreversible fouling. This is because these analytical methods represent an average property of bulk organic matter, while the fouling was actually caused by some specific fractions. It was revealed that hydrophilic fraction of the organic matter was responsible for the irreversible fouling regardless of the type of membranes or organic matter.     

Influence of compatibility between sol and intermediate layer on the performance of yttria-stabilized zirconia nanofiltration membrane

This paper reports the synergistic effect of the sol and intermediate layer on the performance of yttria-stabilized zirconia (YSZ) nanofiltration (NF) membranes. We have focused on the characterization of the microstructure, pure water permeance, and molecular weight cut-off (MWCO) of the NF membranes derived from zirconia sols of different precursor concentrations on two types of supported ZrO₂ ultrafiltration (UF) membranes. We found that the performance of YSZ membranes strongly depends on the sol concentration and the pore size of the intermediate layer. In addition, YSZ gel membrane formation was found to follow the filtration process. Therefore, it is essential to maintain the compatibility between the sol and intermediate layer to fabricate high-performance NF membranes. A crack-free thin YSZ layer with an MWCO of 816 Da (pore size: 1.4 nm) and a water permeance of 25 L m^-2 h^-1 bar^-1 was fabricated using a precursor concentration of 0.03 mol/L, on ZrO₂ UF membrane with a pore size of 5.5 nm. The YSZ NF membrane exhibited a relatively high retention rate towards MgCl₂ (71%), whereas a lower retention rate was observed for NaCl (35%).     

Poly(vinyl chloride) hollow‐fiber membranes for ultrafiltration applications: Effects of the internal coagulant composition

Poly(vinyl chloride) (PVC) hollow‐fiber membranes were spun by a dry/wet phase‐inversion technique from dopes containing 15 wt % PVC to achieve membranes with different pore sizes for ultrafiltration (UF) applications. The effects of the N,N‐dimethylacetamide (DMAc) concentration in the internal coagulant on the structural morphology, separation performance, and mechanical properties of the produced PVC hollow fibers were investigated. The PVC membranes were characterized by scanning electron microscopy, average pore size, pore size distribution, void volume fraction measurements, and solubility parameter difference. Moreover, the UF experiments were conducted with pure water and aqueous solutions of poly(vinyl pyrrolidone) as feeds. The mechanical properties of the PVC hollow‐fiber membranes were discussed in terms of the tensile strength and Young's modulus. It was found that the PVC membrane morphology changed from thin, fingerlike macrovoids at the inner edge to fully spongelike structure with DMAc concentration in the internal coagulant. The effective pores showed a wide distribution, between 0.2 and 1.1 μm, for the membranes prepared with H₂O as the internal coagulant and a narrow distribution, between 0.114 and 0.135 μm, with 50 wt % DMAc. The results illustrate that the difference in the membrane performances was dependent on the DMAc concentration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

High-flux whisker layer ceramic membrane prepared by gel spin-coating method for low-pressure oil/water emulsion filtration

Insufficient permeability and membrane fouling significantly influence the efficiency of ceramic microfiltration (MF) membranes in oil/water emulsion treatment. In this study, a high-flux whisker layer ceramic MF membrane with super-hydrophilicity was successfully fabricated through gel-spin coating method and a low-temperature oxidation method, which was used to separate oil/water emulsion. The effects of the whisker layer and surface wettability were systematically investigated, and the mechanism of in-situ gelling and pore size distribution was proposed. The super-hydrophilic ceramic MF membrane with an average pore size of 250 nm exhibited a high gas flux of 934 m³/(m²·h·bar) and excellent pure water flux of 9754 L/(m² h bar). Even after a long-term circulating filtration process, the super-hydrophilic ceramic MF membrane still maintained a high water flux of over 50 L/(m²·h) at a transmembrane pressure of 5 KPa during the treatment of oil-in-water emulsion with a concentration of 1000 mg/L. Overall, the developed ceramic MF membrane demonstrated high permeability and excellent anti-fouling performance, making it a promising candidate for oil/water emulsion wastewater treatment.     

A General Diagram for Estimating Pore Size of Ultrafiltration and Reverse Osmosis Membranes

Abstract

A slit sieve model has been used to develop a general correlation between the average pore size of the upstream surface of a membrane and the molecular weight of the solute which it retains by better than 80%. The pore size is determined by means of the correlation using the high retention data from an ultrafiltration (UF) or a reverse osmosis (RO) experiment. The pore population density can also be calculated from the flux data via appropriate equations.     

Cellulose nanopapers as tight aqueous ultra-filtration membranes

Recently, we have demonstrated the use of wood-derived nanocellulose papers, herein termed nanopapers, for organic solvent nanofiltration applications. In this study, we extend the use of these nanopapers to tight ultrafiltration (UF) membranes. The feasibility of such nanopaper-based UF membranes intended for use in water purification is shown. Four types of nanocelluloses, namely bacterial cellulose, wood-derived nanocellulose, TEMPO-oxidized cellulose nanofibrils and cellulose nanocrystals, were used as raw materials for the production of these nanopaper-based membranes. The resulting nanopapers exhibit a transmembrane permeance in the range of commercially available tight UF membranes with molecular weight cut-offs ranging from 6 to 25 kDa, which depends on the type of nanocellulose used. These molecular weight cut-offs correspond to average pore sizes of a few nanometres. The rejection performance of the nanopapers is on the border of nanofiltration and UF. We demonstrate that the pore size of the nanopapers can be controlled by using different types of nanocellulose fibrils.     

Recovery of Water from Sewage Effluents using Alumina Ceramic Microfiltration Membranes

Abstract

This work highlights the recovery of water from sewage effluents using alumina ceramic membranes with pore sizes of 0.2 and 0.45 µm respectively in dead‐end filtration mode. The work demonstrates the ability and advantages of alumina‐based microfiltration (MF) membranes in filtering microbes and other harmful pollutants normally present in sewage effluents in dead‐end filtration mode. The fouling behavior of the membranes in the filtration cycle is identified, which in turn helped to regenerate the fouled membranes for subsequent usage. Regeneration studies of fouled membranes also suggest that though chemical cleaning was effective in recovering membrane performance, the fouling had still been progressed slowly and the membranes showed the ability to perform at least five filtration cycles of highly‐contaminated sewage effluents. As expected, the filtration efficiency and flux characteristics at various transmembrane pressure (TMP) of the membranes varies with the pore size of the membrane and is explained in light of Darcy's and Poiseuille's laws of filtration. The results show that alumina ceramic membrane with disc geometry having a pore size of 0.2 µm is more effective in filtering the total suspended solids, turbidity and microbes of the sewage effluents as compare to that of 0.45 µm membrane to a level in which the permeate water appears to be benign for discharging into the surface thereby offering the possibility of recycling or reusing the recovered water from the sewage effluents for suitable purposes.     

Comparative Studies on Coagulation and Adsorption as a Pretreatment Method for the Performance Improvement of Submerged MF Membrane for Secondary Domestic Wastewater Treatment

Abstract

Membrane fouling is the main limitation of water and wastewater treatment. Coagulation and adsorption can remove organic materials which play an important role in fouling phenomena. Thus, this study focused on the comparison of the hybrid process of coagulation and adsorption coupled with microfiltration (MF) membrane for the secondary domestic wastewater from an apartment complex in Gwangju city, South Korea. Coagulation and adsorption were adopted as a pretreatment method prior to MF treatment. Three different powdered activated carbon (PAC) and ferric chloride were used as an adsorbent and as a coagulant. MF was operated in a submerged mode using hollow fiber polyethylene membrane with pore size of 0.4 µm for the separation of suspended organic solids resulted from coagulation or PAC particles, which are used for adsorbing organics dissolved in wastewater. Prior to study on the hybrid system, the performance of coagulation and adsorption processes were optimized individually for the removal of organics. Then, the overall performance for the hybrid system of coagulation/MF and PAC/MF was evaluated based on TOC removal, turbidity removal, and flux decline. It was found that the combined coagulation/MF and PAC/MF showed similar performance for TOC removal while coagulation/MF resulted in a significant decrease of the flux decline.     

Modeling of the Relationship Between Pore Size Distribution and Thickness of Ceramic MF Membrane

The pore size distribution(PSD)measured by the gas bubble point(GBP)method ofceramic microfiltration(MF)membranes prepared by suspension technique was found to be signifi-cantly influenced by the membrane thickness.A culm-like model for pore structure was introduced tocharacterize the membrane pores instead of the conventional model which does not reflect the radiusvariation along the pore passages and is unable to explain the thickness effect on the membrane PSD.A laminate structure,taking the culm-like model for pore structure into consideration,was hypoth-esized for ceramic MF membranes.A mathematical model was then established to quantitativelydescribe the relationship between the membrane number PSD and the membrane thickness.Goodresults were obtained for the correlation of mean pore size and simulation of the PSD for ceramicMF membranes.     

Thin-film nanofibrous composite membranes containing cellulose or chitin barrier layers fabricated by ionic liquids

The barrier layer of high-flux ultrafiltration (UF) thin-film nanofibrous composite (TFNC) membranes for purification of wastewater (e.g., bilge water) have been prepared by using cellulose, chitin, and a cellulose-chitin blend, regenerated from an ionic liquid. The structures and properties of regenerated cellulose, chitin, and a cellulose-chitin blend were analyzed with thermogravimetric analysis (TGA) and wide-angle X-ray diffraction (WAXD). The surface morphology, pore size and pore size distribution of TFNC membranes were determined by SEM images and molecular weight cut-off (MWCO) methods. An oil/water emulsion, a model of bilge water, was used as the feed solution, and the permeation flux and rejection ratio of the membranes were investigated. TFNC membranes based on the cellulose-chitin blend exhibited 10 times higher permeation flux when compared with a commercial UF membrane (PAN10, Sepro) with a similar rejection ratio after filtration over a time period of up to 100 h, implying the practical feasibility of such membranes for UF applications.     

Separation and Fractionation of Oligouronides by Shear‐Enhanced Filtration

Abstract

This paper investigates the separation of anionic oligosaccharides produced by thermal degradation at 120°C of polygalacturonic acids (PGA). Initially, the PGA solution was clarified by two successive centrifugations. These centrifugations were later replaced by two microfiltrations (MF) which did not modify oligosaccharides composition. A dynamic filtration module with a disk rotating at 2000 rpm near a circular organic membrane was used in all filtration steps. Several micro‐ and ultrafiltrations (MF and UF) in cascade (50, 20, and 10 kDa) and a nanofiltration at 1 kDa were used to separate oligomers with degrees of polymerization (Dp) ≤7. Permeate fluxes ranged from 400 Lh^?1m^?2 for the first MF to 240 Lh^?1m^?2 for the 10 kDa UF and 60 to 100 Lh^?1m^?2 for the 1 kDa NF, showing the high potential of dynamic filtration for this application.