This paper reviews current thinking on reverse osmosis (RO) membrane cleaning. It challenges preconceptions and describes novel approaches for the removal of foulants and scale deposits from membrane surfaces. Applying membrane cleaning early in the fouling process before deposits can become compressed is advocated. Waiting until membranes are so fouled that they have a drop in performance of 10-15% as traditionally recommended makes deposits significantly more difficult to remove. The concept of autopsying and cleaning early to reduce underlying fouling rates is explained. The use of recent innovative methods for membrane cleaning is reviewed. New approaches developed by the authors are described and the mechanisms of enhanced cleaning explained. These include use of a cleaning suspension of bubbles, effervescent and high ionic strength cleaners. Enhanced cleaning is observed as a result of agitation of deposits on the membrane surface by different mechanisms which assist foulant removal. Small bubbles are generated during the cleaning process by a combination of different chemical and physical methods. The use of high ionic strength cleaners creates a small flow of permeate across the membrane to the feed side during the soaking period of cleaning. This flow is sufficient to help dislodge foulants on the membrane surface. The authors describe and explain the unique mechanisms of cleaning. Methodology and results of laboratory and pilot plant tests are summarised demonstrating significant improvement in membrane cleaning. This simple technique could easily be applied to existing RO plant restoring efficient RO plant operation.
RO membrane cleaning past, present, future - innovations for improving RO plant operating efficiency