Fouling Control of Spiral-Wound Reverse Osmosis Membrane By Vibration

Reverse osmosis (RO) has become a leading membrane process for wastewater reuse and seawater desalination.  However, concentration polarization and fouling are the inevitable problems which seriously limit the application of RO membrane.  The objective of the study is to develop a novel technology for enhanced control of concentration polarization and fouling in RO membrane processes.  This technique is to apply angular vibration to the spiral wound RO membrane module without stopping of high pressure pump.  The vibration of the vessel is produced by an oscillation generator which is connected to the bottom of the vessel.  In this study, the performance of vibration applied in the lab-scale RO spiral wound module is systematically investigated based on the permeate flux development over a wide range of operation conditions.  The involved operational parameters, including feed quality, cross-flow velocity, vibration frequency, have covered those of interest to practical applications.  And the energy cost for vibration will also be discussed which has great relationship with operational condition.  Although the experiments is still ongoing, the results have demonstrated that vibration was much more efficient in mitigating the rate of permeate flux decline caused by CaSO₄ scaling in comparison with other common foulants such as alginate and silica.  It was confirmed that the turbulence near the membrane surface caused by the relative motion of scaling-forming ions was prone to be strengthened in the presence of vibration.  However, excessive cross-flow velocity or vibration frequency had a negative effect on membrane filtration of CaSO₄ scaling with vibration.  The rate of nucleus formation in the bulk phase increased with increasing in fluid motion which accelerated scaling formation on the membrane surface.  Thus, it is necessary to identify the optimal ranges of vibration frequency and cross-flow, which has significant implication in potential vibration application.