Self-Adaptive Integrated Ultrafiltration (UF)/Reverse Osmosis (RO) Desalination System

The effectiveness of raw feed water filtration in reverse osmosis (RO) membrane desalination is essential to robust operation of RO plants. Feed filtration and other treatments (e.g., chemical additives to suppress mineral scaling and assist in reducing biofouling) are key methods to mitigate RO membrane fouling. In recent years, microfiltration (MF) and ultrafiltration (UF) systems have been increasingly explored for effective RO feed-filtration. While the concept of MF/UF integration with RO is appealing and has met with a reasonable level of success, there are technical challenges in situations where feed water quality fluctuates (with respect to time), and where it is desired to reduce the use of chemical feed additives and membrane cleaning chemicals (for the purpose of both cost reduction and minimizing environmental impact). In meeting the above challenges, a novel concept of self-adaptive UF operation was developed and field demonstrated.  The self-adaptive UF operation integrates a number of novel model-based control and optimization methods and RO/UF design principles that were implemented in a unique “smart” (i.e., autonomous) MF-UF-RO system capable of processing up to about 50,400 gallons per day of raw feed water to a desalination module. This integrated UF/RO system is robust and capable of self-adapting (autonomously) in real-time to a wide range of feed water quality (with respect to fouling propensity) by selecting the appropriate UF backwash strategy. Real-time individual UF module resistance data are utilized in control algorithm to determine the appropriate backwash frequency and intensity for the given feed water conditions. Another unique feature of the UF backwash strategy employed in the current study is the utilization of the RO concentrate for backwashing, which avoid the need for using permeate product water for UF membrane backwash.  Results from extensive field studies for treatment of cooling tower blow down (CTBD) water for reuse and seawater successfully demonstrated the benefits of self-adaptive UF backwashing. The potential use of the present integrated MF-UF-RO approach to distributed deployment of smart water filtration and desalination systems will be discussed with specific focus on operability for ensuring fouling free operation.