往复旋转管式陶瓷膜超滤脱脂奶水溶液的研究

往复旋转管式陶瓷膜过滤系统通过膜组件往复旋转在膜表面反复产生高剪切率,达到减缓膜污染的效果。在相同操作条件下,与单向旋转过滤和死端过滤相比较,往复旋转过滤具有更好的减缓膜污染的作用。本实验利用往复旋转膜过滤装置超滤脱脂奶水溶液,考察了各种参数对该膜系统过滤特性的影响。实验结果表明,料液浓度增大,膜通量减小;过高的操作压差将会抑制膜通量增加;旋转速度增大,膜表面剪切强化作用增强,膜通量相应增大;膜稳态通量随往复旋转周期增大呈现先增大后减小的趋势。当料液速度达到膜组件转速时,瞬时反方向旋转膜组件,膜表面产生最大的剪切率,膜稳态通量也达到最大值。能耗分析表明,往复旋转过滤较单向旋转过滤单位通量能耗低。     

Tubular Membrane Filtration with A Side Stream and its Intermittent Backwash Operation

The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux.     

往复旋转中空纤维膜处理脱脂奶水溶液

采用一种往复旋转中空纤维膜超滤装置处理脱脂奶水溶液,考察了该膜过滤装置的结构参数、膜组件旋转参数以及料液的特征参数等对膜渗透通量衰减的影响。结果表明,旋转角速度越大,膜丝距中空轴轴心越远,往复旋转中空纤维膜的剪切强化作用越好;往复旋转周期的优化则需考虑如何使料液流场流速与膜丝转速之间的矢量迭加在膜表面产生的速度梯度更大,单纯增大或减小旋转周期均会弱化剪切强化的效果。在同样操作参数下,往复旋转方式比死端过滤及单向旋转方式的膜过滤更利于延缓膜通量衰减。     

Separation of casein from whey proteins by dynamic filtration

It has been proven that functional properties of milk proteins can improve the quality and nutritional value of foods. This paper investigates the separation of whey proteins from casein micelles using a Multi Shaft Disk (MSD) module and a rotating disk dynamic filtration module. The MSD module was equipped with 6 ceramic membranes of 0.2 µm pores. PVDF and Nylon membranes of 0.2 µm pores were tested in the rotating disk module. Permeate flux with the MSD module increased with TMP and rotation speed, reaching a maximum of 132 L h^− 1 m^− 2 at 1931 rpm. α-Lactalbumin (α-La) and β-Lactoglobulin (β-Lg) transmissions also increased with rotation speed, ranging from 25% at 1044 rpm to 40% at 1931 rpm . With a Nylon membrane, the rotating disk module yielded lower permeate fluxes than the MSD module, while when equipped with a PVDF membrane it provided higher permeate fluxes than the MSD, but casein micelles rejection was lower. α-La and β-Lg transmissions were higher with the rotating disk module, using Nylon and PVDF membranes, than for the MSD. From this comparison, it can be concluded that the MSD module gave the best compromise between high permeate flux, high α-La and β-Lg transmissions and high casein micelles rejection.     

纳滤/反渗透膜处理重金属废水的性能

The performance of different nanofiltration （NF） and reverse osmosis （RO） membranes was studied in treating the toxic metal effluent from metallurgical industry. The characteristics and filtration behavior of the processes including the wastewater flux, salt rejection and ion rejection versus operating pressure were evaluated. Then the wastewater flux of RO membrane was compared with theoretical calculation using mass transfer models, and good consistency was observed. It was found that a high rejection rate more than 95% of metal ions and a low Chemical Oxygen Demand （COD） value of 10 mg·L^-1 in permeate could be achieved using the RO composite membrane, while the NF rejection of the salt could be up to 78.9% and the COD value in the permeate was 35 mg·L^-1. The results showed that the product water by both NF and RO desalination satisfied the State Reutilization Qualification, but NF would be more suitable for large-scale industrial practice, which offered significantly higher permeate flux at low operating pressure.     

Influence of colloidal fouling and feed water recovery on salt rejection of RO and NF membranes

The influence of colloidal fouling and feed water recovery (or concentration factor, CF) on salt rejection of thin-film composite reverse osmosis (RO) and nanofiltration (NF) membranes was investigated. Fouling experiments were carried out using a laboratory-scale crossflow test unit with continuous permeate disposal to simulate the CF and recovery as commonly observed in full-scale RO/NF systems. For feed waters containing only salt (NaCl), permeate flux declined linearly as CF was increased and salt rejection was nearly constant for both RO and NF membranes. On the other hand, a sharp decrease in permeate flux and significant decline in salt rejection with increasing CF were observed under conditions where colloidal fouling takes place. For both RO and NF membranes, the marked permeate flux decline was attributed to the so-called “cake-enhanced osmotic pressure”. The decline in salt rejection when colloidal fouling predominated was much more substantial for NF than for RO membranes. In all cases, the decline in salt rejection was higher under conditions of more severe colloidal fouling, namely at higher ionic strength and initial permeate flux.     

Use of a Rotating Filter to Enhance Ceramic Membrane Filtration Performance of Latex Dispersions

Abstract

The performances of both the tangential crossflow system and the rotating system with a tubular microfiltration ceramic membrance were investigated experimentally in the separation of latex dispersions. In addition, the shear rate at the membrane surface for azimuthal flow in an annulus with a porous wall on the rotating inner cylinder was solved for the narrow-gap approximation. In contrast to the tangential crossflow system, the rotary system was characterized by a significantly higher flux. The increase in the membrane flux was achieved at shear rates less than those for the crossflow system investigated.     

Flux Characteristics of Oil Separation from O/W Emulsions using Highly Hydrophilic UF Membrane in Narrow Channel

Flux characteristics of oil separation from O/W emulsions using highly hydrophilic polymeric UF membrane has been investigated. The effect of using sub-millimeter filtration channel on both unsteady and steady state permeate flux is evaluated. The time-dependent flux characteristics indicated that membrane fouling has proceeded mainly according to the intermediate pore blocking mechanism modified for crossflow filtration. The steady state flux increased initially with the transmembrane pressure (TMP), then reached a plateau at a relatively low TMP of ～15 kPa, beyond which a steady operation was achieved, and there were practically no advantages of increasing the TMP. The pressure independent limiting flux increased with increasing the crossflow velocity and was found to scale with the membrane surface shear rate to the power of 0.35. The data were modeled satisfactorily using a dimensionally consistent semi-empirical model with R² value of 0.96.     

Numerical simulation of the flow in a rotating disk filtration module

The characterization of the flow inside an experimental flat membrane module with a smooth rotating disk was performed. The module consists of a disk rotating at speeds up to 3000 rpm inside a cylindrical housing equipped with a stationary circular flat membrane. The characterization was carried out by using a finite volume CFD software with the κ-omega turbulence model and results of the range of rotation speeds 300 ≤ Ω ≤ 20000 rpm were compared with experimental and theoretical data reported in previous studies. The simulations suggest high permeate fluxes for the device due to large average shear stresses on the membrane and the absence of stagnant zones inside the module, which are desirable features to avoid membrane fouling processes. The simulations show an overall good agreement with theoretical results based on the main assumption that the wall shear stress on the membrane and on the disk can be predicted using modified correlations for rotating flow over a stationary wall and for flow induced by a rotating disk, respectively and with experimental pressure measurements. It has been found that the flow rate imposed at the inlet of the module has an important effect on the pressure distribution. At the membrane some discrepancies were found between the results obtained with the simulations and with the theoretical approach because of the limitations of the assumptions, especially at low rotating speeds for which the effect of the flow through the module becomes important. The correlations relating the disk rotation rate with the surface averaged pressure and the shear stress on the membrane were determined.     

Reverse osmosis of diluted skim milk: Comparison of results obtained from vibratory and rotating disk modules

This paper investigates the reduction of ionic concentration and carbon oxygen demand (COD) in dairy process waters modelled by one volume of skim milk diluted with two volumes of water using shear-enhanced reverse osmosis. Initial COD and conductivity were, respectively, 36,000 mg O₂ L⁻¹ and 2000 μS cm⁻¹. We have compared the performances of a VSEP vibratory pilot and of a single rotating disk-stationary membrane module equipped with the same Desal AG membrane (Osmonics). Membrane shear rates were varied by changing the vibration frequency in the VSEP and the disk rotation speed or adding radial vanes in the other module. In all tests the permeate COD was reduced below 15 mg O₂ L⁻¹. Permeate fluxes reached a maximum of 180 L h⁻¹ m⁻² at a transmembrane pressure (TMP) of 4 MPa at initial concentration with the VSEP at its resonant frequency and with the disk equipped with 6 mm high vanes rotating at 2000 rpm. Permeate conductivity fell from 60 μS cm⁻¹ at 1 MPa to about 18 μS cm⁻¹ at 4 MPa. In concentration tests, corresponding permeate fluxes at the maximum volume reduction ratio reached (VRR = 8), were 55 L h⁻¹ m⁻² for the VSEP and 60 L h⁻¹ m⁻² for the rotating disk at a TMP of 4 MPa. Permeate conductivities increased exponentially with VRR from 18 to 210 μS cm⁻¹ for the rotating disk and to 250 μS cm⁻¹ for the VSEP. However the mean conductivity of collected permeate varied from 38 μS cm⁻¹at highest shear rate to 60 at lower shear rates. This study shows that these filtration systems permit to obtain reusable water from this high initial COD model effluent with one single reverse osmosis step.     

旋转流强化管式微滤膜的分离研究

利用无机盐SiO2在旋转流场中进行的分离实验研究,对进料方式、悬浮液浓度及压力影响渗透通量的规律进行了探索,结果表明旋转流场的过滤效果比普通十字流的过滤效果显著,而且是一种非常有效的强化过滤方法。     

Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment

Filtration performance and fouling of nanofiltration (NF) and reverse osmosis (RO) membranes in the treatment of dairy industry wastewater were investigated. Two series of experiments were performed. The first one involved a NF membrane (TFC-S) for treating the chemical-biological treatment plant effluents. The second one used a RO membrane (TFC-HR) for treating the original effluents from the dairy industry. The permeate flux was higher at higher transmembrane pressures and higher feed flowrates. The curves of permeate flux exhibited a slower increase while the feed flowrate decreased and the pressure increased. Membrane fouling resulted in permeate flux decline with increasing the feed COD concentration. Furthermore, the flux decline due to the COD increase was found higher at higher pressures for both NF and RO membranes.     

Treatment of Leather Plant Effluent by Membrane Separation Processes

Abstract

A scheme is proposed for the treatment of the leather plant effluent using membrane based separation processes. The effluent coming out from the various upstream units of the leather plant (except chrome tanning) are combined and a two step pressure driven membrane processes involving nanofiltration (NF) and reverse osmosis (RO) are adopted after a pretreatment consisting of gravity settling, coagulation, and cloth filtration. The entire membrane separation scheme is validated by conducting experiments under a continuous cross flow mode. A detailed parametric study for cross flow experiments is investigated to observe the effects of the operating conditions, i.e., the transmembrane pressure drop and the cross flow velocity on the permeate flux and quality for both NF and RO. Using a combination of osmotic pressure and solution diffusion model for both NF and RO, the effective osmotic pressure coefficient, solute diffusivity, and the solute permeability through the membrane are obtained by optimizing the experimental permeate flux and concentration (in terms of total dissolved solids) values for this complex industrial effluent. The BOD and COD values of the finally treated effluent are well within the permissible limits (in India).     

Flux enhancement with glass ball inserted membrane module for the ultrafiltration of dextran solution

The glass-ball-inserted membrane module has been designed to enhance the filtration of a flat-sheet membrane. Three different modes of filtration experiments were conducted and compared to demonstrate the flux enhancement due to the presence of glass balls: normal dead-end filtration, vortex flow filtration, and enhanced vortex flow filtration using glass balls. In the case of enhanced vortex flow filtration, the permeate flux was found to be three times as large as that of dead-end filtration and two times larger than vortex flow filtration. In addition, the flux decline was observed to be relatively low. The effect of the amount of glass balls on the permeate flux was also investigated by changing the glass ball volume fraction from 0.059 to 0.356. It has been observed that the permeate flux shows a maximum value of the volume fraction of 0.119. For the glass-ball-inserted membrane module, the permeate flux tends to increase with the feed flow rate.     

Simulation of continuous stirred rotating disk-membrane module: An approach based on surface renewal theory

A rigorous surface renewal model has been developed describing the aspects of mass transfer in a rotating disk-membrane (RDM) ultrafiltration cell. The model takes into consideration of two distribution functions of random surface elements, one with respect to their point of origin and the other related to the corresponding residence time on the membrane surface. The back transport flux and the permeate flux are evaluated at the membrane surface in order to develop a surface component balance equation. The component balance equation and a flux-rejection relationship arising from irreversible thermodynamics are solved simultaneously to develop a dynamic simulation. The simulation elucidates on permeate flux, membrane surface concentration and the permeate concentration under various operating conditions of transmembrane pressure, bulk concentration, membrane and stirrer speeds. For validation of the proposed model, experiments were conducted with bovine serum albumin (BSA)/water as feed in a standard rotating disk membrane module fitted with polyethersulfone (PES) membrane of 30 kDa molecular weight cut-off (MWCO). The model predicted flux and permeate concentration was found to be in good agreement with the experimental data, and the maximum absolute deviation for both cases was found to be well within ±5%.     

中空纤维膜外压全量过滤动态过程的数值模拟

建立了中空纤维膜外压式全量过滤的CFD模型,模拟膜丝长度、直径、渗透系数、装填密度、污染指数以及跨膜压差不同条件,得到通量分布和产水量的动态演变过程。研究结果表明：通量分布会随着过滤的进行而逐渐变得均匀,这种通量分布的自我调节作用在膜丝较长、较细,渗透性较好,装填密度较高,污染指数较高以及跨膜压差较高时更为明显;产水流量的倒数与累积产水量呈线性关系,但由于通量分布不均匀并且均匀性演变,这种线性关系区别于传统滤饼过滤模型;通过数据拟合得到了适用于中空纤维外压式全量操作的滤饼过滤关联式,可用于预测组件的性能和指导组件的设计。     

Design and performance characterization of a new shear enhanced module with inbuilt cleaning arrangement

BACKGROUND: Shear enhanced membrane modules are becoming popular as they enable high permeate flux in almost all membrane filtration processes due to the high shear rate they generate at the membrane surface. In this article, the design of a new shear enhanced module with unique hydrodynamic cleaning facility is proposed. The device, presently at laboratory scale was named the Spinning Basket Membrane (SBM) module because of its inherent structural similarity with the well known Spinning Basket Reactor. An aqueous solution of polyethylene glycol was chosen as test fluid for the present study. RESULTS: The module was characterized under different parametric conditions of transmembrane pressure (TMP), feed concentration (C₀) and rotational speed of the basket (Ω). It was observed that with its inbuilt cleaning facility the module was able to restrict the flux decline to within 15% of its start up value, even after 21 h of continuous running, with a maximum initial flux as high as 612 L m^?2 h^?1. CONCLUSION: Based on the performance of the module, it may be concluded that this module could be scaled up for nearly uninterrupted industrial operation with reduced requirement for chemical cleaning, which is rare in the membrane industry to date. Copyright © 2012 Society of Chemical Industry     

Control of scale formation in reverse osmosis by membrane rotation

Scale formation of soluble salts is one of the major factors limiting the application of reverse osmosis (RO) membranes. In this study, rotating RO, which takes advantage of Taylor-Couette flow instabilities to reduce concentration polarization and membrane fouling, was investigated as a novel method to control CaSO₄ scale formation. The permeate flux for rotating RO at ω = 180 rpm remains constant up to a volume concentration factor (VCF) of 4.2, while the permeate flux declines steadily with increasing VCF for no rotation. This is probably because vortices in rotating RO induce bulk crystallization and prevent scale particle deposition on the membrane surface. The anti-scaling effect in rotating RO increases with increasing rotational speed and depends to some extent on transmembrane pressure.     

The effects of performance and cleaning cycles of new tubular ceramic microfiltration membrane fouled with a model yeast suspension

The efficiency of crossflow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The experiments that were carried out in the laboratory were conducted to determine and investigate the performance, behaviour and the fouling susceptibility of new ceramic tubular microfiltration membranes during the crossflow filtration of yeast suspensions. The tubular membranes of nominal pore size 0.5 microns were fouled over a varied range of concentration, temperatures, pH, crossflow velocities and system pressures. The typical filtration conditions were at a temperature of 25°C, a system pressure of 1.5 bar and a concentration of 0.03 g/L yeast suspension. These parameters varied during subsequent investigations. After each experiment, the membrane and the rig were cleaned using a three stage cleaning process and was reused in order to replicate industrial filtration conditions. The effects of repeated fouling and cleaning cycles upon membrane flux over time and cleaning efficiency are investigated and their influence over time is also documented. For every experiment, the flux data was recorded over a 50 min period and the membrane was changed after the PWF declined considerably due to excessive fouling over time. Chemical cleaning consisted of a sequential application of a 1% caustic solution through the rig followed by a 2% hypochlorite solution and a 2% nitric solution, all at 50°C. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was developed and established, there appeared to be a leveling of permeate flux. The experimental results are presented in the report and the flux values at different conditions are presented.     

往复旋转式中空纤维超滤膜处理大豆乳清

采用往复旋转式中空纤维超滤膜装置处理大豆乳清液,实验结果表明,该装置利用膜的旋转速度与料液的流动速度之间的矢量叠加,形成较高的速度梯度,从而很好地延缓膜通量的衰减。增大旋转速度或缩短往复周期均会在膜表面形成更大的流体速度梯度,进而产生更好的剪切强化效果,延缓膜通量的衰减。当旋转速度较高时,改变往复周期对膜过滤通量的影响更明显。回归分析表明,膜总透过液量与速度梯度之间存在一个幂函数关系。能耗分析的结果表明,单位通量能耗率随膜表面流体速度梯度的增大而增大,二者之间的关系接近于一个多项式。