| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 99 === Membrane fouling is an unfavorable but inevitable problem in membrane filtration process. Online monitoring techniques can play a major role in understanding its formation mechanism and this may helpful to accomplish a better control over reduction of membrane fouling. Numerous destructive and non-destructive experimental methods were developed for the direct and indirect measurement of cake layer thickness. The present study describes an application of an in-situ optical method to determine the growth of fouling layer by using photo-interrupt sensor. This technique can be effectively used to non-destructively measure or monitor cake thickness as a function of time.
In order to verify the validity of this method, the effect of voltage (10 – 12 V), slurry concentration (0 – 2 g/L), and membrane material (PVDF and PTFE) on sensor signal were examined. In addition, the application of this method for monitoring the growth of fouling cake layer thickness during filtration of high turbidity wastewater under different conditions of flux (50 – 200 LMH), aeration (continuous and semi-continuous at 1 – 1.5 L/min) and suction (continuous and semi-continuous) were studied. The Degussa P25 TiO2 particles were selected for filtration and calibration experiments.
Results showed that as TiO2 particle concentration increases the slope of sensor calibration plot decreases. As input voltage increase from 10 to 12V, results showed that the calibration curve attends more linearity and increased sensitivity at all TiO2 concentration. It was also observed that the sensor signal (voltage) fluctuation at 12V and at higher concentration of TiO2 particles (>1.5 g/L) was higher than that at 10V. The PTFE membrane showed better sensitivity as compared to PVDF membrane.
From the filtration experiment it was observed that at lower flux the fouling is more at the bottom than at the top of the membrane. But as the flux increases the cake layer become more and more uniform. It was also observed that TMP rise was not so severe at low flux due to low and irregular fouling. But at high flux the TMP increases rapidly and attends a constant value. The cake thickness around entire surface area of the membrane was suppressed due to continuous aeration. The semi-continuous aeration could also suppress the membrane fouling at the same level as observed at continuous aeration. The combination of suction and relaxation at different conditions can only reduces the growth rate of fouling cake layer thickness, but extent fouling was not suppressed. The application of suction and backflow mode with sufficient backflow period conditions can suppress the fouling drastically to the same extent that observed during semi-continuous aeration condition.
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