Measurements of Growth Rate of Filter Cake in Vertical Single-Pass Ultrafiltration Using Hollow Fiber Membrane Module

Vertical ultrafiltration experiments of silica colloid and bovine serum albumin solution were conducted in the single-pass mode by using a hollow fiber membrane module and beneficial in measuring the time evolution of the growth rate of the filter cake during filtration. The extremely small mass flux of the concentrate enabled us to highly concentrate the feed solution on the principle of vertical ultrafiltration in which the filter cake formed on the membrane surface is exfoliated continuously. Both growth and re-entrainment rates of the filter cake formed in vertical ultrafiltration were evaluated from the experimental data of the filtration rate and the mass fraction ratio of the concentrate on the basis of the mass balance within the hollow fiber membrane module. As a consequence, it was found that the re-entrainment rate of the filter cake increased almost linearly with the filtration time in the initial period of filtration and then tended to rapidly approach a constant value. The filter cake stopped growing under this dynamically balanced condition. The variations of the average specific resistance of the filter cake with time were also determined from the time evolutions of both the filtration rate and the growth rate of the filter cake.     

Nanocolloid cake properties determined from step‐up pressure filtration with single‐stage reduction in filtration area

A sophisticated method was developed for evaluating simultaneously and accurately both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as protein solution and nanosilica sol. In the method, a step‐up pressure filtration test was conducted by using a filter with a single‐stage reduction in the effective filtration area. The influence of the pressure drop across the cake on not only the average specific cake resistance but also on the average cake porosity of highly compressible filter cake was evaluated using only flux decline data in one dead‐end filtration test, taking advantage of the decrease in the cake thickness caused by the pressure increase. As a result, the cake properties were easily determined for a variety of nanocolloids. Constant pressure dead‐end ultrafiltration data obtained under various pressures and concentrations were well evaluated based on the method proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4426–4436, 2015     

Cake properties of nanocolloid evaluated by variable pressure filtration associated with reduction in cake surface area

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869–3877, 2014     

Periodic Ultrafiltration by Single-Pass Flow Using Hollow Fiber Membrane Module

Abstract

Periodic ultrafiltration of bovine serum albumin (BSA) solutions by single-pass flow was conducted using a hollow fiber membrane module. In this method the filter cake formed on the membrane surface during filtration was disrupted by periodically interrupting filtration. Thus, a much higher filtration rate, which led to an increased concentration ratio of protein solutions, was provided by periodic operation compared with what was produced by continuous operation. Influences of filtration times (θ_f) and sweeping times (θ_d) on the filtration performance were examined.     

Unified model for the prediction of consecutive solid–liquid filtration and expression at the constant pressure

Unified nonlinear model is proposed for the prediction of consecutive solid–liquid filtration and expression at the constant pressure. This model is based on the Darcy–Terzaghi filtration-consolidation equations modified to consider power-law pressure dependence of the specific cake resistance, and transforming Darcy law to the linear form. The model considers nonuniform structure of compressible filter cakes obtained by filtration and following expression. The profiles of local compressive pressure and local cake characteristics are simulated and compared for different moderately and highly compressible filter cakes (H.K. kaolin, CaCO₃, silica, activated sludge) based on the analytical and numerical solutions of the model. It is shown that the behavior of solid–liquid expression depends from the initial structure of compressed materials. Consolidation ratio U of the filter cakes with initially nonuniform structure formed by filtration differs from that of semi-solid materials with initially uniform structure. Different methods of determination of consolidation coefficient are analyzed and compared for nonuniformly structured filter cakes.     

Approach from physicochemical aspects in membrane filtration

In membrane filtration, solution environment factors such as pH and solvent density are important in controlling the filtration rate and the rejection of the particles and/or the macromolecules. The filtration rate and the rejection in membrane filtration have been investigated from physicochemical aspects. It was shown that the properties of the filter cake formed on the membrane surface play a vital role in determining the filtration rate in mem-brane filtration. It was clearly demonstrated that such filtration behaviors as the filtration rate and the rejection are highly dependent on the electrical nature of the particles and/or the macromolecules. Furthermore, it was shown that the solvent density ρ has a large effect on the steady filtration rate in upward ultrafiltration.     

Detailed investigation of effects of operating parameters of ultrafiltration using laboratory-scale ultrafiltration unit

Cross flow ultrafiltration is a pressure driven membrane process in which the fluid to be filtered flows parallel to the membrane surface. The formation of filter cake can be reduced by scouring force of the flow, thus better permeate rate is obtained.

Laboratory-scale ultrafiltration experiments with Polyvinyl Alcohol (PVA) solution of known molecular weight was carried out to study the membrane filter performances with respect to operating parameters. These operating parameters included, membrane molecular weight cut off size, molecular weight of PVA, influent concentration, cross flow velocity and applied pressure. It was discovered that clogging in the membrane occurs quite slowly during first 30 minutes, and quasi-steady state was noticed normally after 50 minutes of filtration time. In this study, steady state flux data were used to develop semi-empirical and empirical correlations which are useful in the optimum design of ultrafiltration.     

Clarification of liquids using filter aids Part I. Mechanisms of filtration

Filter aids were characterized by an effective particle diameter and a pore diameter in the filter aid cake, calculated from the specific cake resistance using the Kozeny equation. The results agreed well with those from mercury porosimetry. The transition from surface filtration to depth filtration by filter-aid cakes was studied with uniform polystyrene particles as a model impurity. The critical ratio between pore diameter and impurity diameter was between 2 and 3. At conditions of non-surface filtration, an important concentration of impurity exists in the liquid flowing through the cake causing a danger of blocking. When pre-coat and body feed were used with polystyrene particles as an impurity, the blocking appeared to occur rather easily on top of the original pre-coat and on the filter medium. The type of pre-coat and the way in which it was formed were very important. In beer filtration, which is mainly a surface filtration, a small concentration of passing impurity was able to block the pre-coat layer, when the filter aid of the body feed was coarser than that of the pre-coat.     

Filtration mit kompressiblen Kuchen: Effiziente Konzeptefür eine anspruchsvolle Trennaufgabe

Efficient Process Strategies for Compressible Cake Filtration Compressible cake filtration is a challenging and often critical task in many industrial processes. Conventional design methods are not always appropriate as they fail to address the specifics of compressible structures. Efficient strategies for compressible cake filtration will be presented. The guidelines for process design and optimization are the outcome of experimental investigations, utilizing an innovative compression‐permeability‐filter cell, and a process simulation based on a rigorous model of compressible cake formation and consolidation.     

Local solidosity of microcrystalline cellulose during dead-end filtration and sedimentation

Solid–liquid separation by filtration and sedimentation are important operations used in a wide range of industries. One important characteristic of both the filtration and sedimentation processes is the solidosity of the filter cake/sediment that is formed, affecting the efficiency and design of the separation. In this study local solidosity was investigated using a γ-attenuation method during both filtration and sedimentation experiments for microcrystalline cellulose, a highly crystalline cellulose with particles of about 2–80 μm in diameter. Constitutive relationships for the solidosity were investigated using both filtration (i.e. cake build-up and expression) and sedimentation data for experiments at different pH and suspension concentrations. The sedimentation behaviour under these different conditions was also investigated. It was found that a three parameter empirical model could be used to describe the constitutive relationship between local solidosity and local solid compressible pressure for the sediment formed and the filter cake after both cake build-up and expression. This correlation worked well for the material investigated even at low solid compressible pressures.     

一种基于膜污染指数的超滤膜污染评价方法

利用浸没式中空纤维膜小试系统,基于膜污染指数（FI）建立超滤膜污染的评价和试验方法。通过试验考察超滤膜污染变化规律,以及运行周期对膜污染指数计算的影响,并确定计算膜污染指数的运行周期;并对膜污染指数评价方法的可重复性进行检验：对化学清洗前后膜污染指数进行比较。试验表明,在过滤初期,滤饼污染和吸附污染并存,所以初期水力不可逆膜污染指数（HIFI）增长较快;中期超滤膜的吸附能力不断减弱,膜污染主要是滤饼污染,所以膜污染较为稳定：后期跨膜压力过大,压缩滤饼层,减小滤饼孔隙率,增加滤饼阻力,所以HIFI有所增加。同时短期的膜污染试验可以用来反映长期的膜污染情况,该超滤膜污染的评价方法重复性好,污染后的超滤膜经过化学清洗后。可以重复利用。     

Efficiency of wood cellulose filtration

木浆纤维素作为助滤剂应用广泛,其过滤性能亟待研究。不同的过滤条件对木浆纤维素滤饼层的过滤性能会有很大影响。本文通过单因素法考察了过滤压力对滤饼层截留精度和平均滤速的影响,并通过正交实验法考察了木浆悬浮液黏度、木浆浓度、木浆添加量、悬浮液含水对滤饼层截留精度和平均滤速的影响。实验表明木浆纤维素属于中等可压缩性物料,其过滤性能随过滤条件变化呈规律性变化。通过对实验结果的分析,确定了优化方案。研究结果为木浆纤维素过滤的小型工业试验提供参考。     

铝系混凝剂减缓膜污染的红外光谱-多变量曲线分辨分析

超滤是一种高效的水处理技术,近年来被广泛应用于工业废水处理、生活污水回用、海水淡化预处理等领域。然而,超滤长期运行会造成膜污染。本文采用了在线混凝结合超滤工艺,使用不同形态的铝系混凝剂（硫酸铝、氯化铝或聚合氯化铝）,处理含有不同溶解性有机质组分（腐殖酸、牛血清白蛋白和高岭土）的模拟原水,研究不同铝形态、不同组分及其相互作用对超滤膜污染过程的影响。本研究建立了流量衰减模型模拟膜污染过程,结合衰减全反射红外光谱（IR-ATR）和多变量曲线分辨-交替最小二乘法（MCR-ALS）的数据处理方法对膜上的多种污染物进行定性和定量分析。结果表明硫酸铝和氯化铝混凝剂均可明显提高膜比通量,减缓膜污染。该工艺混凝剂投加量低于常规处理工艺即可明显减缓膜污染。混凝剂投加量为0.4mg/L时,氯化铝混凝效果较好,混凝剂投加量为2.4mg/L时,硫酸铝混凝效果较好。低投加量（0.2mg/L、0.4mg/L）下,PAC对缓解膜污染程度不明显,反而加重膜污染。牛血清白蛋白对超滤膜的污染比腐殖酸严重。因为牛血清白蛋白的存在大大降低了混凝的效果,阻碍疏松滤饼层的形成。向原水中投加硫酸铝混凝剂,膜污染主要发生在过滤前期,即...     

Cross-Flow Microfiltration of Bacillus Subtilis Broths under Various Culture Times

Bacillus subtilis broths under different culture times are filtered in a cross-flow microfilter. The operating condition effects, such as cross-flow velocity, transmembrane pressure, and broth culture time, on the filtration flux, cake properties, and extracellular polymeric substances (EPS) transmissions are discussed thoroughly. The culture broths contain B. subtilis cells and EPS which is characterized as polysaccharides (hydrocarbons) and proteins. An increase in broth culture time leads to higher concentrations of cells, soluble and extractable EPS. The total protein to polysaccharide concentration ratio in the broths is ca 0.2. However, the soluble polysaccharide concentration is 10-fold higher than that of soluble proteins. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. However, the impact of cross-flow velocity is more significant. The filter cake resistance formed by B. subtilis cells and EPS flocs plays the most important role in determining the overall filtration resistance. The mass and average specific filtration resistance of cake can be estimated using a force balance model and empirical equations. The cake structure and thickness are analyzed using SEM. A thicker and more compact cake may be formed under longer broth culture time. Most soluble polysaccharide and protein molecules have the opportunity to penetrate through the cake and membrane into the filtrate because the solute transmissions are measured as high as 0.75–1.0. The influences of operating conditions on the polysaccharide and protein transmissions are negligible. Therefore, to enhance filtration flux by increasing transmembrane pressure or cross-flow velocity is beneficial to improve separation efficiency, especially by increasing cross-flow velocity.     

Numerical modelling of filtration with and without sedimentation runs

From experimental batch runs of filtration with sedimentation above the cake formed, a procedure is proposed and applied to experimental data for obtaining the relationships between the settling solids velocity in the hindered settling zone, the local specific resistance and the effective pressure and the solids concentration. Considering the material and momentum balances in the hindered settling zone above the cake, in the cake and in the filter membrane, a simulation program was obtained that satisfactorily reproduces the experimental runs of filtration with sedimentation runs. This simulation work confirms the hypothesis considered in the theory of filtration with sedimentation runs, e.g. the fact that the characteristic lines arise tangently from the cake surface. In addition, the method developed for obtaining the different relationships considered has been demonstrated as correct. The simulation of filtration without sedimentation runs (stirring the suspension above the cake) has also been studied.     

聚乙烯醇(PVA)对模拟胞外聚合物(EPS)在错流超滤中膜污染的影响

研究了在模拟胞外聚合物(EPS)溶液中添加聚乙烯醇(PVA)对错流超滤膜过滤过程的影响. 对有无添加PVA的模拟EPS溶液分别用错流平板膜进行超滤实验,用Hermia修正模型对实验数据进行拟合,分析验证膜污染机理. 结果表明,无论是否添加PVA,模拟溶液的通量-时间实验数据对滤饼堵塞模型的拟合度都最高,为0.891~0.994;添加PVA的模拟EPS溶液形成的吸附阻力和膜污染阻力均比无添加的溶液高约0.5倍,滤饼比阻比无添加的溶液高约4倍,分别为2.29′1014和9.57′1014 m-1;模拟EPS溶液添加PVA后,通量对操作压力的敏感度增加,对膜面流速的敏感度却降低.     

Investigation of the fundamental assumptions relating compression-permeability data with filtration

A recently reported investigation indicates several inaccuracies in the methodology of compression-permeability (C-P) testing which suggest that previously reported agreement between C-P and filtration data may be fortuitous. Until now, there has been no separate and direct confirmation of each of the two assumptions necessary to obtain a unique correspondence between C-P and filtration data. The first assumption that the specific filtration resistance is a function solely of cumulative-drag-stress is generally accepted. Direct proof requires that the parabolic filtration equation, which is derived primarily on this assumption, describes both incompressible and compressible cake behavior. Most materials produce compressible cakes and “a priori” screening to find an incompressible cake requires identification of a material (Geon) that produces a cake with a linear axial pressure distribution. Results show that the parabolic filtration equation fits both types of cake behavior but an equation based on constant filtration resistance describes only incompressible cake behavior. To engineering accuracy and for dilute slurries, the assumption is verified. The second assumption that the cumulative-drag-stress equals the cake pressure drop is a macroscopic force balance and experimental verification requires a filter chamber designed to measure both of these quantities. A theoretical development, based on integral averaging, and experimental results both indicate that the ratio of cumulative-drag-stress to cake pressure drop correlates extremely well with cake porosity. A unique one-to-one correspondence between C-P and filtration data is not possible without “a priori” knowledge of filter cake porosity. Previously reported agreement between C-P and filtration data can probably be attributed to the L/D dependence of C-P specific filtration resistances. Consequently, C-P data can be used as a research tool to simulate filtration data but predicted filtration times based solely on C-P data can be in considerable error.     

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。     

The Role of Polysaccharide on the Filtration of Microbial Cells

The role of polysaccharide on the “dead-end” microfiltration of microbial cells is studied. Yeast and blue dextran are used as typical samples of microbial cells and polysaccharide, respectively. The filter cake becomes more compressible in the early periods of filtration and exhibits much higher filtration resistance when dextran molecules co-exist in the cake structure. A cake compression mechanism is proposed to explain the pressure effects on the cake structure and filtration resistance. For the two-component cakes, the dextran molecules deform easily even under a pressure as low as 30 kPa, while significant yeast deformation is observed when pressure is higher than 100 kPa. It is attributed to the depletion of most solid compressive pressures by deformed dextran molecules. The cake porosity data indicate that the cake compressibility is higher under low filtration pressure, and blue dextran plays a significant role on the cake structure and occupies a considerable volume in the cake. A resistance model is also derived for understanding the relationship between the average specific cake filtration resistance and filtration pressure. The cake filtration resistance is determined by the effective volume fraction of each component in cake and nearly the same as that of blue dextran under low pressure.     

Decreasing Filter Cake Resistance by Using Packing Structures

Packed beds used in absorption columns are evaluated to determine whether they can also be beneficial for cake‐forming filtrations. To assess this, model systems are characterized and separated by using a dead‐end filter cell. Filtrations are conducted with different packings; the filtrate amount over time and resulting turbidity are evaluated. Packings increase the filter cake resistance and the separation time of the cakes formed with approximately incompressible solids. However, they exhibit a positive effect on the filtration of a more complex, compressible substance; the process is not only accelerated, but also the quality of the obtained filtrate is not compromised. These results demonstrate potential in the use of packed beds for the filtration of complex biogenic suspensions.