| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 91 === The combination of shearing action and electric field has been recognized as an effective means of reducing both concentration polarization and membrane deposition in crossflow filtration. However, such a process has not yet received wide acceptance. One of the reasons for that is the excessive operation cost due to a high energy requirement. In order to minimize the power consumption, attention has been directed to the use of pulsed electric field. There have been brief reports that the use of pulsed electric field can lead to substantial improvements in filtration rates, but so far, the understanding of the principles of such processes is very limited.
In order to investigate the characteristics of pulsed electro- microfiltration for separating microbial cell suspensions, the experiments with yeast suspensions (with and without washed) by a flat-channel filter were carried out to show the effect of electric field strength and pulsed frequency on the filtration rate and the protein transmission when the suspensions were prepared from yeast/BSA mixtures.
When the filter was imposed with constant electric field strengths, its filtration rate increased almost linearly with the strength, but the increasing rates were greater than that of yeast mobility determined using electrophoretic measurement. The phenomenon that an instantaneous change of filtration rate associated with the imposed on or off of the pulsed electric field indicated clearly that the electroosmosis plays the major role in enhancing the filtration rate.
Among the four pulsed frequencies used in the study, in the range of on(10~120)/off(10~120), on(30)/off(30) always gives the better performance in increase of filtrate rate and its filtrate amount obtained was 94~82% of that from constant E ranging from 1000 to 4000 V/m. Thus, the pulsed operation has an obviously high electric energy efficiency. Based on the results under constant electric field strength and that without electric field, the average pseudo-steady state filtration rate in pulsed operation was also estimated and which values are somewhat lower than the experimental data, especially for the higher electric field strength.
For the filtration with yeast/BSA mixtures, it was observed that the electroosmotic and filtration rate are affected significantly by the zeta potential of BSA. The results obtained from the condition of pH=5, very near the isoelectric point of BSA, indicated that the transmission of BSA through the 0.2μm membrane is larger than 91% and increases with the electric field strength. However, a nearly constant transmission about 91% is observed for the pulsed operation with on(30)/off(30), independent of electric field strength used.
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