Analysis of Gravity Filtration Behaviors of Waterworks Sludge Based upon Sedimentation Tests

Both gravity filtration experiments under constant pressure conditions and gravity sedimentation experiments were conducted using the municipal waterworks sludge. It was clarified from the theoretical analysis that the effect of sedimentation on the filtration rate was noticeable for the sludge used in this study. The local specific flow resistance at various sludge concentrations was determined by the sedimentation velocity method. The local porosity was related to the local solid compressive pressure by the sedimentation equilibrium method. The decline behaviors in the filtration rate in gravity filtration accompanied by sedimentation were well evaluated only from the sedimentation data based upon the sedimentation velocity method and the sedimentation equilibrium method.     

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.     

Modeling of Particle Fouling and Membrane Blocking in Submerged Membrane Filtration

Abstract

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is also derived. In order to estimate the shear stress acting on the membrane surface, the diameter, shape, and rising velocity of air bubbles are analyzed based on hydrodynamics. Once the model coefficients are obtained, the pseudo‐steady filtration flux under various conditions can be estimated by the proposed model and the basic filtration equation. The calculated results agree fairly well with the available experimental data.     

Effect of Interparticle Potentials and Sedimentation on Particle Packing Density of Bimodal Particle Distributions During Pressure Filtration

Effect of interparticle forces, bimodal particle size distribution, and slurry viscosity on particle packing in alumina bodies consolidated by pressure filtration is presented. The requirements for packing colloidal particles to their highest density are strong repulsive interparticle forces and optimum particle size distribution. Even though these conditions are met, the high packing density in consolidated bodies may be adversely affected by particle segregation resulting from sedimentation. Therefore, the slurry during consolidation must have a sufficiently high viscosity to prevent sedimentation.     

The Effect of Polymeric Flocculants on Settling and Filtration of Iron Ore Slimes

Abstract

During the wet processing of iron ores, a substantial amount of fine particles known as slimes are generated in downstream which need to be recovered effectively for their usage and beneficiation. Besides water from slime ponds overflow remains contaminated with very fine particles which are difficult to settle and cause environmental pollution when contaminated water is discharged to the downstream river. The settling behaviour in the slime pond gets affected in particular when ore contains hydrated oxides. The above problems necessiatate to study the settling and filtration behaviour of the slimes by means of effective flocculants. The flocculants namely, amylopectin-g-polyacrylamide (Ap-g-PAM), sodium alginate-g-polyacrylamide (SAG) were synthesized by graft copolymerization using redox initiated catalyst. The high molecular weight flocculants, namely, magnafloc (1011) superfloc (N 300) were used for comparative studies. The present paper reports the settling and filtration behaviour of iron ore slimes.

The experiments show that sedimentation rate increases with increasing flocculant dose upto a certain limiting value. The settling rate decreases with increasing the pulp density. The volume of filtrate increases with increasing flocculant dose. The filtration efficiency of synthesized polymer is comparable with the commercial one, i.e., magnafloc (1011) at natural pH.     

Particle Deposition in Laminar Crossflow Filtration of Power Law Slurry

Abstract

A theoretical model for predicting the probability of particle deposition in crossflow filtration of power law slurry is developed. The model is based on the critical angle of friction between depositing particles, which can be estimated by analyzing the forces exerted on the particles. The binding force between the particles due to polymer adsorption plays an important role in the particle deposition. The smaller the flow behavior index of the slurry is, the larger the binding force and the higher the probability of particle deposition will be. The effects of operating conditions such as the crossflow velocity of the slurry and the filtration rate on the probability of particle deposition are also discussed in depth. The calculated values of the probability of particle deposition agree fairly well with the experimental data. A program is designed to simulate the packing structure and the porosity at the cake surface. The porosity increases not only with the increase of the crossflow velocity, but also with the increase of the flow behavior index of the power law slurry.     

滤饼过滤过程的计算机模拟程序设计

详细介绍了滤饼过滤过程中各物理量的计算公式、计算机模拟程序的设计 ,为滤饼过滤过程的研究提供了一种新的研究方法     

动态错流过滤研究的最新发展动态

动态错流过滤从理论发展到实践的应用,国内外在这方面做了大量的研究,取得了一定的成果。本文将近些年国内外的最新研究作一个全面总结,以便为以后开展相关的工作提供一些有用资料,同时能对理解错流过滤有所帮助。     

离心过滤中滤饼含液量影响因素的研究

本文对离心过滤中影响滤饼含液量的主要因素进行分析。选择细粒级的五种物料，在三足式过滤离心机上做脱液实验，获得的脱水和动力学试验数据，经因次分析，计算机处理，得到实验条件下滤饼含液量Ｗｔ的准数方程：研究结果表明：影响滤饼含液量的因素，首先是物料的物理性质：固体密度ρｓ，颗粒表面积体积平均粒径ｄｓｖ和悬浮液粘度μｓｕｓｐ；其次是操作参数：转鼓角速度ω，脱液时间ｔ和滤饼厚度ｈ。实验条件：Ｆｒ＝１０４８～１５１０，ｄｓｖ＝１．２９～２４．８μｍ，μｓｕｓｐ＝１～１０ｍＰａ·ｓ     

Effect of Support Material Properties on Dynamic Membrane Filtration Performance

A dynamic membrane is defined as a cake layer which forms on a support material, for example, filter cloth or mesh when the liquid to be filtered includes suspended particles. Formation of an effective dynamic cake layer is highly related with the retention of particles on the support material surface. Therefore, support material properties are considered to be of prime importance in the performance of dynamic membrane treatment systems. This study investigates the effect of support material properties including pore size and structure of the material on dynamic membrane formation and performance. In this concept, a comparative evaluation was made between support materials which have different yarn types. The results showed that high total suspended solids removal efficiency (>98%) could be achieved by using dynamic membrane filtration technology. Mono-monofilament and staple filter cloths were determined as the most appropriate materials in terms of the critical fluxes which were 9.2 L/m² · h and 17–19 L/m² · h for mono-mono filament and staple materials, respectively. However, considering the results of more long-term experiments, mono-monofilament filter cloth was found more suitable for cake layer accumulation. Therefore, we postulate that mono-monofilament cloth can be used in dynamic membrane filtration systems as an alternative to traditional membranes in anaerobic membrane bioreactors.     

滤饼过滤过程的计算机模拟研究

利用自行设计的计算机模拟程序 ,对物料粒度、浆体浓度、过滤压差对过滤脱水的影响以及滤饼分层现象进行了计算机模拟 ,并通过实验进行了验证。结果表明 ,模拟结果虽然在数值上与实验结果有一定差距 ,但定性方面能够很好地与实验结果相吻合。     

Modelling the Effect of Particle Size in Microfiltration

Abstract

Particle deposition at the filter surface in microfiltration is studied to better understand the effect of particle size on cake morphology and permeability reduction. Numerical simulations are carried out on a Hele Shaw cell which consists of a representative unit element of a two dimensional spatially periodic flat plate with pores. The particle concentration in the fluid is assumed to be low so that particles enter one by one into the computation domain. Particles follow the flow streamlines under creeping flow conditions from a random initial location until they are subjected to physico‐chemical interactions near the filter surface or a particle already deposited. The computational domain consists of two regions: a fluid region and a porous medium region, i.e. the particle cake. The flow over the two regions of the Hele Shaw cell is computed using the Darcy model, including the variations of the permeability field due to the cake formation. Results show that both the permeability and the filtration efficiency are affected significantly by particle size.     

旋管动态过滤的实验研究

在自行开发的小型旋管压滤实验装置上 ,以清水和白刚玉微粉为物料 ,对旋管动态过滤进行了实验研究。结果表明 ,提高旋管转速反向离心压差增大 ,使清水的透过速率减小 ,转速的变化还会影响沉积滤饼层的厚度和比阻     

旋转圆筒型过滤器精密平衡过滤O/W乳浊液特性研究

以油分（煤油）浓度较低的（ｋｅｒｏｓｅｎｅ）Ｏ／Ｗ（ｗａｔｅｒ）乳浊液为对象,通过旋转圆筒型过滤器进行精密过滤,对影响平衡过滤的油分滤饼层的压缩性,以及过滤速度与诸操作因子间的关系进行了探讨。结果表明高速旋转的圆筒型过滤膜对附着在过滤膜表面的滤饼产生很大的扫流力,具有不断扫流过滤膜表面上生成的滤饼的特性,因此对难过滤性Ｏ／Ｗ乳浊液进行高速精密过滤具有广泛的实用价值。     

聚丙烯酰胺对赤泥沉降和过滤的影响

研究了阴离子型、阳离子型和非离子型聚丙烯酰胺对赤泥沉降和过滤的影响。结果表明 :三种型式的聚丙烯酰胺均可作为赤泥的沉降助剂 ,但阴离子和非离子型不宜用作赤泥的过滤助剂 ,阳离子型则在赤泥的过滤过程中表现出了一定的助滤作用。     

橡胶促进剂M过滤分离工艺实验研究

由于橡胶促进剂M在酸化后含有大量的水分,前期研究表明通过添加表面活性剂预处理可以有效降低固液分离后滤饼的含水量。为了研究经表面活性剂处理后悬浮液的过滤方法与效果,分别采用加压过滤、真空抽滤、离心过滤的分离方法进行了过滤分离实验,并对不同分离方法下滤饼质量进行检测。研究结果表明,采用真空抽滤方法对添加表面活性剂预处理后的橡胶促进剂M悬浮液进行过滤分离,并通过水洗滤饼,可以大幅度降低滤饼的含水量,并能满足橡胶促进剂M的质量要求。     

Effect of Pore Size and Particle Size Distribution on Granular Bed Filtration and Microfiltration

Abstract

The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.