Monitoring of Membrane Scaling and Concentration Polarization in Spiral-Wound Reverse Osmosis Module Using Ultrasonic Time-Domain Reflectometry with Sound Intensity Calculation

Xianhui Li, Genghong An, Jiebin Lin, Jianxin Li



Ultrasonic time-domain reflectometry (UTDR) with a sound intensity calculation was used to monitor membrane scaling and concentration polarization in a 4-inch spiral-wound reverse osmosis module. Three focused transducers with the frequency of 2.25 MHz were located equidistantly on the module along the feed flow direction. The scaling experiments were carried out with 1.0 g/L and 2.0 g/L calcium sulfate for 90 h fouling. Results show that the membrane surface suffered from more severe fouling at the high solution concentration of 2.0 g/L CaSO4. And the fouling degree gradually increased along the flow direction of RO module. Furthermore, the sound intensity obtained at the solution of 1.0 g/L CaSO4 gradually increased during the fouling process, whereas the sound intensity obtained at solution of 2.0 g/L CaSO4 gradually decreased to minimum at first, then increased due to concentration polarization as well as the deposition and growth of fouling layer. Moreover, the initial induction time in the change of sound intensity is related with the degree of concentration polarization. It could be an indicator for the start of foulant deposition. The independent methods such as SEM and weight measurements were in good agreement with the ultrasonic observations.

Keywords: Reverse osmosis; membrane scaling; concentration polarization; ultrasonic time-domain reflectometry (UTDR); sound intensity