以光學探針法線上監測高濁度進水 薄膜過濾之污塞層厚度變化之研究

Online Monitoring of Fouling Layer Thickness Variation in Membrane Filter for High Turbidity Influent Treatment Using Photo-interrupt Sensor

戴牧恬(Hemlata-Rahul Damodar)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/碩士(2011年)

https://doi.org/10.6840/CYCU.2011.00109

摘要

在薄膜過濾的過程中，薄膜積垢(fouling)問題是難以避免的。為了解決這個問題，必須先了解薄膜積垢的形成機制，以便降低薄膜積垢程度。而即時偵測技術在這當中，便扮演了一個非常重要的角色。薄膜積垢的量測有各種不同的方式，有破壞性的、非破壞性的、直接的以及間接的方式。本研究描述一種原位光學偵測系統(in-situ optical method)，此種系統使用光遮斷感應器測定薄膜積垢層的成長。此技術可有效的以非破壞性的方式，量測或偵測薄膜積垢層的厚度與時間推移的關係。
本研究測試不同操作條件下所生成之薄膜積垢厚度，並隨時接收即時偵測系統所產生的訊號，以為分析之用。薄膜種類選用PVDF膜與PTFE膜，進料泥漿粒子為商業型二氧化鈦粒子(Degussa P25 TiO2)。本研究以改變電壓值、進料液濃度及其相互搭配所造成之影響，探討各種操作條件對薄膜積垢厚度所造成之影響。之後，亦應用此種方式進行高濁度進料液過濾過程中，積垢層厚度成長狀況的偵測；其中，為探討各種條件對積垢層生成厚度的影響，在過濾過程中改變不同的條件：包括使用連續式或間歇式真空過濾、改變不同進料通量(50-200LMH)、於過濾同時連續或間歇式通氣體並變換氣體流量大小。
量測準確度分析研究結果顯示，當粒子濃度越大，偵測器所產生之校正曲線的斜率會越小。當進料壓力從10伏特增至12伏特，校正曲線會更趨於線性，且對於二氧化鈦濃度的變化反應會更靈敏。本研究亦觀察到，在12伏特以及二氧化鈦濃度高(>1.5 g/L)的狀態之下，偵測器的訊號波動較10伏特時來的嚴重。而薄膜積垢造成偵測器的訊號波動，於PTFE薄膜上會較於PVDF薄膜上來的嚴重。而由過濾實驗中可觀察到，低通量時薄膜積垢較易產生不均勻的狀況，但若通量增加，則積垢層會較均勻。在低通量時，也由於不均勻的積垢層而使得透膜壓的升高趨緩，但於高通量時，透膜壓則會迅速的升高然後持平。若於過濾同時連續通氣體，可有效抑制整個薄膜表面積垢層的生長；採用歇式通氣體，同樣可得到與連續通氣體一樣的效果。另外，間歇式真空過濾無論在何種條件之下，都還是能抑制積垢層的生長，但抑制效果並不非常顯著；反之，若使用連續式真空過濾或經過足夠時間的反洗，則可有效的抑制積垢層生長。

關鍵字

薄膜積垢 ； 光學探針 ； 線上監測

並列摘要

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.

並列關鍵字

membrane fouling.submerged MBR ； photo-interrupt sensor ； online monitoring

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