Air bubbles enhance membrane cleaning: a future perspective
Air bubbles generated using a novel micro-bubble generator have displayed a dramatic enhancement in cleaning efficiency when used in conjunction with specially formulated cleaning chemicals. In order to establish the effect of this application on membrane performance, a series of experiments were conducted using both a flat sheet test rig and a small scale pilot plant. Experiments show that the size of the bubbles had a dramatic impact on the effects of cleaning. Air bubbles generated in combination with commodity chemicals are large and produce an inconsistent flow. However, in the presence of specially formulated cleaning chemicals, air bubbles become much smaller and refined (micro-bubbles), creating a pulsating-like action. This eases foulant removal and ultimately restores membrane performance to a greater magnitude. In addition to bubble size, the speed of the feed pump proves to be another important factor. An optimum flow speed and bubble size has been determined to achieve the best possible conditions for enhanced cleaning effects. Cleaning effectiveness was quantified by; flux increase, salt rejection increase, turbidity increase of the cleaning solution and by visual inspection of the membrane. Cleaning with air restores membrane performance to a greater extent than without air. Membranes from several major membrane manufacturers were used in this study to determine membrane compatibility with air. Membranes were then subsequently autopsied at Genesys labs in Madrid to establish the impacts of cleaning and whether the micro-bubbles had caused any damage to the membrane surface. A variety of analytical techniques were used including Scanning Electron Microscopy and Infra-Red Spectroscopy. Autopsy results are discussed in another paper. In this paper, the authors describe the equipment use, experimental methodology and results of cleaning with this novel approach.