Impacts of Aging and Chemical Cleaning on the Properties and Performance of Ultrafiltration Membranes in Potable Water Treatment

The impacts of aging and chemical cleaning on the properties and performance of ultrafiltration membranes in potable water treatment were investigated using membrane samples from a full-scale water filtration plant. A range of analytical tools were employed to characterize various membrane attributes, encompassing flux, tensile strength, morphology, surface resident functional groups, and both organic and inorganic foulants. The results of laboratory experiments that simulated chemical cleaning sequences were consistent with those observed in the full-scale water filtration plant, in terms of their effects on the properties of the membranes. It was revealed that aging played a significant role in the deterioration of the tensile strength of the membrane media, as well as the degradation of the intensity of surface resident functional groups, which led to the accumulation of foulants. While cleaning with hypochlorite resulted in a decrease of membrane tensile strength, identical cleaning with citric acid had no such effect. The degradation of membrane tensile strength may be correlated to a decrease in the intensities of functional groups as measured by Fourier transform infrared spectroscopy (FTIR). These results suggest that the concentration of hypochlorite and the cleaning duration should both be minimized to reduce their negative impacts on membrane properties.     

Purification of Ellagic Acid by UF Membranes

Ellagic acid (2, 3, 7, 8‐tetrahydroxy(1)benzopyrano(5, 4, 3‐cde)(1)benzopyran‐5, 10‐dione) was selected as a model pollutant which is present in the tannic fraction of cork processing wastewater. The ultrafiltration of aqueous ellagic acid solutions through three membranes was studied in tangential UF laboratory equipment. Two of the membranes were polyethersulfone (Biomax10K and Biomax5K, with MWCO of 10000 and 5000 Da, respectively), and the third made of regenerated cellulose (Ultracel5K, with MWCO of 5000 Da). The water hydraulic permeability was evaluated for each membrane. The evolution of the permeate flow rate with processing time was followed, and the influence of the main operating variables (feed flow rate, trans‐membrane pressure and nature of the membranes) on the permeate flux was also established. According to the hypothesis of the film theory, the intrinsic and apparent rejection coefficients, as well as the mass transfer coefficients, were also determined, and the values obtained were discussed as a function of the operating conditions used.     

Retention of Biopolymers by Ultrafiltration Membranes

Separation of biopolymers is one of increasingly important applications of ultrafiltration (UF) membranes. The efficiency of separation is often evaluated through pilot experiments and seldom predicted. Available predictions focus on correlations between UF pore width and biopolymer hydrodynamic diameter, while overlooking key operational parameters including transmembrane pressure (TMP). The role of TMP in the retention of biopolymers is revealed, i.e., magnification of TMP leads to decreased retention of the particulates. No full retention of the biopolymers without a rigid outer shell has been observed. Pressure‐induced stretching of flexible biopolymers and expansion of membrane pores are the possible reasons of deteriorating selectivity. A division into flexible and rigid biopolymers provides a better prediction of membrane selectivity.     

反渗透膜用于中水回用时的污染和化学清洗

介绍了反渗透膜用于中水回用时的污染原因及化学清洗过程,采用酸洗与碱洗相结合的清洗方式能够较好地恢复反渗透膜的性能。对于深度污染的膜,通过延长循环和浸泡时间,以及添加剥离分散剂能提高反渗透膜的通量。     

Ultrafiltration Carbon Membranes from Organic Sol-Gel Process

We present a simple approach for preparing mesoporous carbon membranes on macroporous fly-ash-based ceramic supports via sol-gel polymerization of resorcinol with formaldehyde. The support was dip-coated and dried at 45°C under ambient pressure without a special drying process. The mesoporous carbon membrane was obtained after carbonization under a nitrogen atmosphere. The coating–pyrolysis process only required one cycle. The graphitization degree increased with carbonization temperature, as shown by X-ray diffraction. However, Raman spectroscopy revealed that defects emerged at high carbonization temperature. Scanning electron microscopy clearly showed the mesoporous carbon layer and macroporous support, a uniform carbon layer with thickness less than 1 µm forming on the support. The obtained carbon membrane shows uniform pores and high mesopore volume. The flux of pure water through the mesoporous carbon membrane was as high as 167 L · m^?2 · h^?1 · bar^?1. The molecular weight cutoff of this membrane was found to be about 20,000 Da.     

Modeling of Fouling in Three Ultrafiltration Cell Configurations: Swirl,Plane and Axial Annular

Membrane fouling is a complex phenomenon induced by various chemical or physical factors. Several models can be used in order to predict flux. In this paper, models extracted from the literature are compared with experimental data collected in our laboratory during ultrafiltration of bentonite suspensions for three different cell designs (a classical plane unit and two annular units, one fitted with a tangential inlet inducing a swirling decaying flow, the other generating a pseudo axial flow). Mass transfer coefficients are measured by means of an electrochemical method for the two axial cell designs and are further included in the gel model predicting the limiting ultrafiltration flux. In ultrafiltration, the particles retained by the membrane will accumulate in the immediate vicinity of its surface to form a layer of higher particle concentration involved in the gel model. This concentration is also determined experimentally. Nevertheless, the gel model is not able to predict the permeation flux during ultrafiltration of bentonite suspensions in different cell designs. A modification of the erosion model, which takes into account the cell configuration, is also presented.     

无机分离膜在应用过程中的污染清洗方法

无机膜分离技术是国际上最先进的分离技术之一,膜污染的清洗是膜应用过程中的一个重要问题。阐述了膜污染的性质,总结了膜污染清洗的各种物理方法和化学方法,并对无机膜材料的耐化学腐蚀性能进行了分析,为无机膜的应用维护提供了一定参考。     

L‐Lysine Monohydrochloride Syrup Concentration using a Membrane Hybrid Process of Ultrafiltration and Vacuum Membrane Distillation

The development of energy saving membrane separation processes is finding a unique position in process industries. One of the important areas where they are employed is the biotechnology industry. This industry has its own specifications and requirements, e.g., levels of diluteness, thermal, chemical and shear fragility. Membrane separation processes have the characteristics necessary to match these specifications and needs. In this research, the determination of the experimental concentration of L‐Lysine monohydrochloride (L‐lysine‐HCl) syrup was investigated using ultrafiltration (UF) and vacuum membrane distillation (VMD) hybrid membrane processes. Four parameters that are known to have significant influence on the UF process were examined, i.e., pressure difference across the membrane, feed concentration of L‐lysine‐HCl, feed velocity on the membrane surface, and pH. For the VMD unit, pressure difference and pH were replaced with feed temperature and vacuum pressure on the permeate side of membrane. Each process was carried out separately and the results were used to design a bench‐scale process. In order to save time and money, the Taguchi method of experimental design was employed. The effects of feed concentration, pressure difference across the membrane, feed velocity on the membrane surface, and pH on the target variable, i.e., the membrane flux, in the UF process were 39.93, 38.65, 9.36, and 9.59 %, respectively. For the VMD process, these values were 64.79, 22.16, 6.21, and 2.14 % for feed temperature, feed concentration, vacuum pressure on the permeate side, and feed velocity on the membrane surface, respectively.     

细金属分离膜的性质及应用研究

对原来专用于扩散法分离同位素的镍基金属管状分离膜的性质和市场应用进行理论和实验研究。通过实验分析其孔径大小、孔径分布等基本性质,再加以深入的市场调研,从原理上推断其更为广泛和高经济效益的实际应用,并以实验验证。     

Effect of Conditioning Ultrafiltration Membranes on their Performances in Electrodialysis with Ultrafiltration Membrane

Abstract

A recent alternative method based on ultrafiltration membrane stacked in an electrodialysis cell was recently used for the separation of bio‐active high added value charged molecules, such as peptides and polyphenols. However, the ultrafiltration membranes which are uncharged membranes present lower electrical conductivity, in comparison with conventional ion‐exchange membranes. The purpose of this study was to evaluate the effect of conditioning ultrafiltration membranes of different molecular weight cut‐off (MWCO) (10, 20, 50, and 100 kDa) in solution with different ionic strength (distilled water and 0.1 M NaCl_(aq)) on their electrodialytic properties. It appeared that the conditioning solution could have a major impact on the electrical conductivity value of an ultrafiltration membrane and that the final conductivity value after soaking increased with an increase in molecular weight cut‐off. However, the soaking period and solution had no effect on membrane thickness. Furthermore, the electrical conductivity of the membrane was increased after an electrodialysis with ultrafiltration membranes process of a salt solution.     

Effect of Fouling Conditions and Cake Layer Structure on the Ultrasonic Cleaning of Ceramic Membranes

Abstract

Homogeneous alumina membranes fouled by polystyrene latex particles at different pH values and ionic strengths were subjected to ultrasonic cleaning. Cleaning was more effective at high and low pH than at neutral pH. At low pH values, less repulsive particle‐particle interactions resulted in the removal of millimeter‐scale aggregates and highly effective cleaning. At near‐neutral pH, stronger repulsive particle‐particle interactions caused detachment to occur as individual particles from the cake layer rather than as flocs, which was a slightly less effective cleaning mechanism. Ultrasonic cleaning of cake layers formed at high ionic strength (>0.3 M KCl) was less effective than cleaning at lower ionic strength (<0.3 M KCl). High ionic strength caused particles to coagulate in solution and deposit as flocs on the membrane surface forming a highly permeable fouling layer. This fouling layer was resistant to ultrasound at the sub‐optimal cleaning conditions used in this study, perhaps due to particle attachment occurring within a primary energy minimum. Membrane cleaning experiments performed with particles of varying size showed that particle size was less important than the surface potential of the particles. For a given mass, particles that possessed the largest surface potential formed the thickest fouling layer, irrespective of particle size, and showed the greatest improvement in flux with ultrasonic cleaning. These results demonstrate that solution conditions influence ultrasonic cleaning of membranes primarily by modifying particle‐particle and particle‐membrane interactions as well as cake layer structure, rather than by impacting the extent or magnitude of cavitation events.     

微滤和超滤过程中浓差极化和膜污染控制方法研究

本文较全面的介绍了微滤和超滤过程中浓差极化和膜污染的各种控制方法,并比较了各种方法的优缺点。     

Commercial Integrated Permeate Channel Ultrafiltration Membranes: Design,Modeling and Performance

Submerged ultrafiltration membranes for use in wastewater treatment have been practiced for several decades and is becoming the standard for water reuse applications. In this paper, the characteristics of the unique and robust Integrated Permeate Channel (IPC®) membrane are presented for membrane bioreactor (MBR) applications. The design choices made during the 10-year development of the IPC® membrane translate in key product attributes that the end users are looking for: a high capacity of clean permeate per footprint at the lowest cost of total ownership over the lifetime of the product.     

Effect of Poly(vinyl pyrrolidone) on Antifouling Properties of Asymmetric Poly(ethylene‐co‐vinyl alcohol) Membranes

Poly(ethylene‐co‐vinyl alcohol)/poly(vinyl pyrrolidone) (EVAL/PVP) blend membranes with antifouling properties were prepared by nonsolvent induced phase separation. Residual PVP in the sample was calculated by infrared spectroscopic data and confirmed by thermogravimetric analysis. The effect of residual PVP on hydrophilicity and permeation characteristics of the membranes was evaluated. Porosity and equilibrium water content of the membranes were influenced by the addition of PVP. The effect of protein fouling on flux using bovine serum albumin as a model system was studied in detail. The residual PVP content could enhance the antifouling property of the membrane. All membranes proved to have sufficient mechanical strength to withstand pressure‐driven filtrations.     

Synthesis and Characterization of Polycarbonate/TiO2 Ultrafiltration Membranes: Critical Flux Determination

A novel polycarbonate (PC) membrane was modified with titanium dioxide via nonsolvent-induced phase separation method to improve its hydrophilicity and antifouling properties in a submerged membrane system for the removal of humic acid (HA) both with and without polyaluminum chloride (PAC) coagulant. The effect of TiO₂ additive on the morphology and performance of the nanocomposite membranes was studied by atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray, mechanical properties, water contact angle, porosity, pure water flux, rejection tests, and antifouling parameters. The obtained results revealed that a higher critical flux was achieved by the PC/TiO₂ nanocomposite membrane. The flux recovery ratio of the neat PC membrane increased with the addition of TiO₂ nanoparticles and without PAC coagulant. HA removal for the PC nanocomposite membrane was higher than that of the neat PC membrane with and without PAC coagulant.     

聚偏氟乙烯/有机累托土纳米复合超滤膜的制备、表征和性能研究

用溶液插层法制备了聚偏氟乙烯(PVDF)/有机累托土(OREC)纳米复合超滤膜,研究了OREC含量对复合膜力学性能、表面粗糙度、微观形貌、结晶行为和亲水性的影响,并测定了复合膜的性能。结果表明:OREC的加入对复合膜微观形貌有重要影响,使膜的孔隙率从44.6%增加至71.3%;OREC的加入有利于PVDF中亲水性β相的生成,在其含量较高时能显著提高复合膜的表面粗糙度和表面亲水性,并能同时提高复合膜的纯水通量和蛋白截留率;刚性OREC片层的加入,能显著改善复合膜的力学性能,对弹性模量的增强尤为明显,可达纯PVDF膜的5.8倍。     

Surface Modification of Ready-to-Use Hollow Fiber Ultrafiltration Modules for Oil/Water Separation

Reusing wastewater from oil-related industries is becoming increasingly important, especially in water-stressed oil-producing countries. Before oily wastewater can be discharged or reused, it must be properly treated, e.g., by membrane-based processes like ultrafiltration. A major issue of the applied membranes is their high fouling propensity. This paper reports on mitigating fouling inside ready-to-use ultrafiltration hollow-fiber modules used in a polishing step in oil/water separation. For this purpose, in-situ polyzwitterionic hydrogel coating was applied. The membrane performance was tested with oil nano-emulsions using a mini-plant system. The main factors influencing fouling were systematically investigated using statistical design of experiments.     

Membranes in Biotechnology

Membranes have become an integral part of biotechnological processes. They have proved to be useful tools for the retention of biocatalysts in industrial biotransformations. This paper describes the development of membrane reactors and the application of membrane‐based processes in biotransformations. Membrane systems for substrate dosing (e.g., aeration), catalyst retention (e.g., ultrafiltration), product separation (e.g., pervaporation), and salt removal (electrodialysis) from solutions are dealt with. The use of membranes in bioelectrochemistry is also discussed.     

Polyimide Ultrafiltration Membranes with High Thermal Stability and Chemical Durability

Abstract

Asymmetric ultrafiltration membranes based on poly[(4,4′-oxydiphenylene)pyromelliteimide] were produced by wet technique from prepolymer casting solution, followed by solid-phase conversion of the prepolymer membranes into polyimide insoluble form at 200°C. It was demonstrated that by adding benzimidazole to the casting solution and filling of prepolymer membrane pores with inert high-boiling oil prior to thermal treatment allow us to prepare asymmetric porous polyimide membranes. The main characteristics of the membranes obtained (permeability coefficients and molecular weight cut-off) match those typical to ultrafiltration membranes. It was found that the developed asymmetric ultrafiltration polyimide membranes have excellent thermal and chemical resistance. The membranes retain rigidity above Tg (360°C) and are chemically stable at temperatures up to 400°C. The developed membranes are resistant against swelling and dissolving in aggressive and organic media including amide solvents.