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A systematic study has been made of the factors which influence compressibility in cake filtration. A fully automated dead-end pressure filtration rig was designed, constructed and assembled at Loughborough and used to provide accurate data for an experimental matrix. The parameters investigated included pressure, feed concentration, time, surface charge, size and shape of the particulate material and scale of filtration. A proven electrical resistance measuring technique was used to determine transient solids concentrations through a filtering cake/suspension and subsequently interpret filtration performance. The particulate materials calcite and zinc sulphide dispersed in water were used to span a range of filter cake compressibility. The initial results from experiments using calcite were found to be reproducible and generally followed the expected trends. More compressible materials, such as zinc sulphide, were subsequently filtered at different pHs to investigate the influence of surface charge. Filter cells of different filter sizes were used to examine the influence of scale on filtration. Several curious observations were made such as sudden increases in filtrate rate at apparently stable process conditions and lower concentration measurements near the base of the cake. The importance of considering all scale-up parameters and their relation to each other is highlighted in the work. Further points such as the definition of compressibility over a narrow range of pressure and the structure of the filter cake have been discussed. The results were analysed with the use of conventional and new filtration theories. The conventional and modem theories generally gave good predictions of cake height for all the materials tested but for unstable/compressible suspensions the prediction of the concentration profile was less accurate. The use of the maximum solids concentration value at the base of the cake has been suggested to reduce this error and so help prevent filter under sizing. Results indicating retarded packing compressibility have been discussed along with volume-time data which suggest an influence of scale on filtration. Scale-up constants were found to vary considerably in some cases. Large changes in cake resistance were seen for small changes in cake concentration suggesting a need to use other structural characterising parameters as well as macroscopic cake concentration values. The Koenders and Wakeman model gave good predictions of the first linear part of the volume-time relationships for stable suspensions. Conclusions are drawn on the influence of each of the studied parameters on the filtration of compressible materials.

This work is concerned with an alternative method for metal ion removal from aqueous solutions - surfactant enhanced ultrafiltration. Surfactant monomers aggregate above a certain concentration, specific to the surfactant, to form micelles. Anionic surfactant micelles will attract and bind metal cations. Free metal ions and surfactant monomers pass freely through an ultrafiltration membrane, but if the micelle-metal ion complex is sufficiently large it is rejected. Research reported in this thesis has been carried out on well defined aqueous solutions containing only one type of metal ion together with the natural surfactant lecithin. Lecithin is a food grade by-product of the soybean processing industry and it was chosen because it is non-toxic, biodegradable, abundant and inexpensive. It has a high molecular weight of about 750 Daltons and forms large size micelles. The main aim was to identify the basic mechanisms which influence the permeate flux and rejection levels of the process. The project was carried out in three stages. Stage one was the characterisation of the feed solution which included the determination of the critical micelle concentration using surface tension measurements, measurement of micelle size and zeta potential using a Malvern zeta sizer and visualisation of the micelle shape using scanning electron microscopy of freeze fractured lecithin solution droplet. In the second stage filtration experiments were carried out at a wide range of lecithin concentrations, metal ion concentrations and operating conditions. The experiments were run for 5 hours, by which stage a steady state condition was reached in all cases. Permeate samples were taken after I, 3 and 5 hours. Permeate flux was monitored throughout the experiment. The following properties were monitored for the feed solution at the beginning and the end of each experiment and for all permeate samples: lecithin concentration, copper concentration, pH, conductivity. In the 3 stage Electron Dispersive Analysis by X-ray (EDAX), Scanning Electron Microscopy (SEM) and a X-ray Photoelectron Spectrum Technique (XPS) were employed to investigate any membrane feed solution interactions. The results of the 3 stages were used to identify the basic mechanisms which control the permeate flux levels and the extent of component rejection in lecithin enhanced ultrafiltration.

The work presented in this dissertation provides a novel technique of manipulation of colloidal entities during membrane filtration based on an AC electrokinetic phenomenon called dielectrophoresis. First, the influence of dielectrophoretic (DEP) forces created on a membrane surface to levitate colloidal particles is studied both theoretically and experimentally. A numerical model based on the convection-diffusion-migration equation is presented to calculate the concentration distribution of colloidal particles in shear flow under the influence of a repulsive DEP force field. The simulation results indicate that particle accumulation on the membrane (or membrane fouling) during filtration can be averted by creating a repulsive DEP force field on the membrane surface. Corresponding experimental study employs a microelectrode array on a glass surface in a tangential flow cell, to apply repulsive DEP forces on polystyrene particles suspended in an aqueous medium. Applying a non-uniform AC electric field on the microelectrodes generates the DEP force field that levitates the polystyrene particles above the surface. This study indicates that the repulsive dielectrophoretic forces imparted on the particles suspended in the feed can be employed to effectively mitigate membrane fouling in a crossflow membrane filtration process. The second phase of the study is aimed at controlling colloid transport through a microporous membrane using DEP forces acting across the pores. A theoretical analysis of colloid transport through straight cylindrical capillaries in the presence of a non-uniform AC electric field is developed. Numerical simulations demonstrate that the interaction of the particles with the electric field generates strong repulsive DEP forces, acting selectively on the colloidal particles to control particle transport through the pore. A combination of DEP forces and size exclusion in porous material is proposed to develop an energy efficient technique for colloid filtration. Experimental results on this steric-dielectrophoretic filtration are also obtained using novel ``sandwich membranes" and colloidal suspensions in a dead-end filtration system. The primary advantage of this steric-dielectrophoretic mechanism is that the filtration can be achieved by filter media (such as membranes) that have considerably larger pore sizes than the retained colloids. The technique can also result in tunable filtration mechanisms, where particles with same size but different electrical properties can be separated using suitably designed membranes. / Fluid mechanics, Electrokinetic filtration

Thesis (Ph. D.)--Ohio State University, 1987. / Includes bibliographical references (leaves 143-149). Available online via OhioLINK's ETD Center

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: J. Thomas Sims, College of Agriculture and Natural Resources. Includes bibliographical references.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2009. / Title from PDF title page (University of Texas Digital Repository, viewed on Sept. 16, 2009). Vita. Includes bibliographical references.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Littles, Jerrol W. Jr., Committee Member ; Johnson, W. Steven, Committee Member ; Kurfess, Thomas R., Committee Chair ; Melkote, Shreyes N., Committee Member.