超声波在线监测卷式反渗透膜污染及清洗

In situ monitoring of membrane fouling and cleaning in spiral-wound RO modules by ultrasonic time-domain reflectometry

应用超声时域反射法和信号拟合及量化模型在线监测卷式反渗透膜元件污染及清洗过程.实验采用三个2.25MHz高频聚焦探头和商业卷式反渗透膜组件,污染液为1.0g/L硫酸钙.清洗阶段包括纯水冲洗、浸洗与酸洗三部分.结果表明,超声信号能够穿透组件外壳而进入多层膜结构.观察发现随膜表面污染物沉积而超声信号发生系列有序变化.此外,随膜表面污染物沉积、结构变化以及污染层形成,声强不断减小至最低,后期趋于稳定.研究还发现,沿进料液流动方向,信号变化诱导期趋于变短,而且,污染物优先靠近出口处沉积;越靠近料液出口,信号变化幅度越大,污染越严重.这是由于沿轴向不断加剧的浓差极化所致.在清洗阶段,随着膜通量恢复超声信号变化表现出一致性.

The study describes the ultrasonic time-domain reflectometry with a sound intensity model for monitoring membrane scaling and cleaning in a spiral-wound reverse osmosis element. Three focused transducers with the frequency of 2.25 MHz and the commercial spiral-wound RO module were used. The scaling experiments were carried out with 1.0 g/L calcium sulfate and the cleaning process consisted of three different phases： pure water flushing, immersion cleaning and acid-washing. Results showed that the ultrasound generated by the focused transducer is capable to penetrate through the multiple layers of membrane. The systematic changes in ultrasonic signals had also been observed during the fouling process. The results of sound intensity revealed that the corresponding sound intensity gradually decreased to minimum with the deposition of the foulant on the membrane and then kept constant as the formation of fouling layer. Further, with different initial lag phases on different ports, the scales gradually deposited and more and more along the feed flow direction with the fouling process due to concentration polarization. Moreover, the membrane flux and sound intensity recovered step by step with the cleaning processes. The results obtained by independent methods were in good agreement with the observations by ultrasonic technology.