Ultrasonic-time-domain-reflectometry as a real time non-destructive visualisation technique of concentration polarisation and fouling on reverse osmosis membranes

[摘要] ENGLISH ABSTRACT: Fouling is readily acknowledged as one of the most critical problems limiting thewider application of membranes in liquid separation processes. A betterunderstanding of fouling layer formation and its monitoring is needed in order toimprove on existing cleaning techniques. Plant operation can be optimised if foulingcan be monitored by noninvasion means either on the plant itself or on an attachedmonitoring device.The overall scope of this research was to develop a non-destructive, real-time, in situvisualisation technique or device for concentration polarisation and fouling layermonitoring. Ultrasonic-time-domain-reflectometry (UTDR) was employed as avisualisation technique to provide real-time characterisation of the fouling layer.A 24 cm-long rectangular flat sheet aluminium cell was designed and used asseparation device for a desalination system. The experimental results obtained usingthis module confirmed that there are an excellent correspondence between the fluxdecline behaviour and the UTDR response from the membrane. The ultrasonictechnique could effectively detect fouling layer initiation and growth on themembrane in real-time. In addition to the measurement of fouling, the ultrasonictechnique was also successfully employed for monitoring membrane cleaning. Sinceno real-time permeation data is available during cleaning operations in industrialapplications, a UTDR monitoring device may prove to be a very valuable techniquein optimising cleaning strategies.The technique was further tested on an 8-inch diameter spiral wrap industrialmodule and good results were obtained. Stagnant zones, as well as flux flowbehaviour inside the module could be determined. However, more research ISneeded to fully understand the complex phenomena inside a spiral wrap module.Overall, the UTDR technique and its use in monitoring devices have a major impactin the membrane industry due to its extremely powerful capabilities.

[发布机构] Stellenbosch University