超声监测技术在膜分离过程中的应用研究

在膜分离过程中，膜通量总是随运行时间而下降．为了区分膜污染与浓差极化或者可能的膜形变对通量的影响，和选择适宜的清洗过程，对一种只敏感于膜表面状况的超声测量方法进行了广泛研究．通过平板膜(包括微滤膜、超滤膜和反渗透膜)以及卷式反渗透膜过程的应用实例，说明了这种实时、在线的超声时域反射法即Ultrasonic Time-Domain Reflectometry (UTDR)可以利用它的反射波的振幅和回声抵达超声传感器的时间来监测浓差极化、膜污染(例如CaSO4污染)与清洗过程，也可以用来测量膜的压紧度和污染层厚度．超声测量与传统膜性能测量结果有良好的关联，并具有区域性测量的特性．为了实用化目的，新近的研究进展也作了介绍．

Study of using in-situ ultrasonic measurement technique in membrane separation

During membrane-based separation processes,flux through the membrane decreases over time.Many studies have established that membrane compaction,concentration polarization,and fouling can contribute to this flux decline.However,there has been no appropriate methodology for distinguishing these phenomena via real-time measurement.For this purpose,the use of ultrasonic time-domain reflectometry(UTDR)was described.UTDR can be set-up to respond only to changes that occur on the membrane surface,thus also making this a useful technique for membrane cleaning processes.Results are reported from studies using foulants such as calcium sulfate in flat-bed as well as commercial spiral-wound RO membrane modules.Data show that UTDR could be successfully utilized to monitor and distinguish the concentration polarization,fouling and cleaning processes by the measurement of the amplitude and arrival time of the ultrasonic reflections.The UTDR results correlated well with the changes in the permeate flux even though UTDR is a site-specific measurement.Also,UTDR signals can be used to determine the extent of membrane compaction and the thickness of the fouling layer.To develop the potential of this UTDR technique for on-line monitoring of commercial membrane separations,recent researches are presented.