Scaling in reverse osmosis desalination plants: A perspective focusing on development of comprehensive simulation tools
Regarding RO-membrane scaling, a major issue of practical significance is the adequacy and reliability of available methods to assess feed-water scaling propensity, select and optimize scaling control schemes, and monitor membrane scale-formation during plant operation. An overview is provided herein of the complicated mechanisms involved in scaling within the compact RO membrane modules, and of approaches employed to control and monitor scaling. Based on this assessment and review of experimental work, focusing on the early period of membrane scaling, the inadequacies are identified of the aforementioned methods. For modeling and quantifying incipient scaling, the rate of scale-mass deposition per unit membrane-surface-area (in g/m2 h) emerges as the most appropriate parameter. Emphasis is placed on development of a comprehensive predictive tool for the above applications, particularly in the early stage of RO-plant overall-design and optimization, when operating conditions should be selected and account taken of chemicals and energy needed to control scaling. To tackle systematically this demanding task, leading to a reliable process simulator, it is suggested to combine results from well-designed small-scale membrane-scaling tests with theoretically-sound modeling of desalination module performance. Efforts in that direction are outlined as well as progress made and main challenges.