Nobuyuki Katagiri

Filtration Behaviors in Constant Rate Microfiltration with Cyclic Backwashing of Coagulated Sewage Secondary Effluent

The constant rate microfiltration characteristics of sewage secondary effluent pretreated with polyaluminum chloride (PACl) have been investigated. In order to reduce membrane fouling, the periodic operation of constant rate microfiltration and backwashing cycles was conducted using the fully automated experimental apparatus with the monolithic ceramic membrane module. As filtration proceeded, cake formation occurred on the membrane surface, causing an increase in pressure drop. Backwashing could reduce the flow resistance that resulted from the formation of the filter cake. However, the initial pressure drop seemed to increase after each backwashing due to the irreversible pore blocking of the membrane. Based on the intermediate blocking law, a mathematical model has been developed to describe the pore blocking behavior. Using the model in combination with the filtration rate equation for the compressible cake, the energy consumption has been evaluated for the whole process. The experimental results were in good agreement with those calculated from the theoretical model. Optimum operational conditions for an energy efficient process were suggested based on analytical results. The reclaimed water is found to be free from microorganisms and can be reused in applications such as toilet flushing or car washing.

Compression-Permeability Properties of Compressed Bed of Superabsorbent Hydrogel Particles

The average pore size of the gel network of a superabsorbent hydrogel particle was evaluated based on the data of the permeation rate of water through the compressed bed of gels obtained with the use of a compression-permeability cell (C-P cell). The pore size evaluated based on the Happels cell model using the C-P cell data was compared with that obtained from the Kozeny-Carman equation in which the Kozeny constant k was assumed to be 5.0. It was clarified that the use of k = 5.0 in Kozeny-Carman equation underestimated the pore size compared to the calculations using the Happels cell model. Moreover, the effect of bound water in the gel was clarified.

Compression and filtration characteristics of yeast-immobilized beads prepared using different calcium concentrations

ABSTRACT Yeast cells were immobilized on calcium alginate beads prepared using different calcium concentrations. The compression properties of the immobilized beads (e.g., softness index and retardation time for compression) were strongly affected by the calcium concentration. The effects of the bead properties on filtration characteristics, such as cake porosity, specific cake filtration resistance, cake compression creeping effect and cake compressibility, were analysed using a dead-end filtration system. The filtration curve of yeast-immobilized beads had an “S” shape, similar to that of soft gel particles. The cake compression behaviour and variation in cake properties were directly reflected on the curve trend. The Voigt in the series model was employed to describe variation in cake porosity with time during a compression. The yeast immobilization increased the bead softness; therefore, the porosity of a cake formed by yeast-immobilized beads was lower than that formed by pure calcium alginate beads. The cakes formed by yeast-immobilized beads possessed a high compressibility of approximately 1.0 and a high softness index of approximately 1.5. The beads prepared using lower calcium concentrations had higher softness, shorter retardation times for compression, higher cake compressibility, lower cake porosity and higher specific cake filtration resistance. The results demonstrated that immobilizing yeast cells on calcium alginate beads is beneficial for retaining higher yeast activity than that of freely suspended yeast. However, the activity levels of yeast immobilized using different calcium concentrations were nearly the same after 3 h. Therefore, using high concentrations of calcium for yeast immobilization is beneficial for improving yeast activity and filtration characteristics.

Evaluation of compression-permeability characteristics of microbial cake based on microfiltration data

ABSTRACT A method was developed for evaluating the compression-permeability characteristics of microbial cake based on the microfiltration data on microbial suspension. The parameters in newly proposed equations, which were applicable to extremely-high compressible cake, were determined to fit the data of the average specific resistance and average void ratio of the filter cake as functions of the filtration pressure. The calculations based on proposed equations were in good agreement with the compression-permeability cell data such as the local specific resistance and local porosity of the cake represented as functions of the local compressive pressure in all microorganisms used in this study.

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.