Application of Micro–Nano Bubbles to Improve the Performance of Reverse-Osmosis Membrane against the Gypsum Scaling

Abstract

The present study investigated the effects of air micro–nanobubbles (AMNBs) on calcium sulfate dehydrate (gypsum) scaling over a reverse-osmosis (RO) membrane in a lab-scale plate-and-frame module processing brackish water. Membrane performance for the treatment of a synthetic solution sample with high gypsum scaling potential was evaluated by measuring permeate flux and salt rejection and high-resolution scanning of fouled membrane surface in the presence and absence of AMNBs. The results show that AMNBs significantly reduce gypsum scaling on the membrane surface due to enhanced dispersion effect in flow and decrease the effect of concentration polarization (CP), especially in central areas and the outlet of the channel flow. In the absence of AMNBs, after 20 h of scaling, the membrane permeate flux and salt rejection reduced to 70% and 96.4%, respectively. However, the presence of AMNBs in the solution improved these values notably in the same conditions (flux-83% and rejection-98%). The results indicate that the application of AMNBs is able to play an effective role in the control of gypsum scaling and improvement of membrane performance in the RO desalination process.