(555a) Self-Adaptive Operation of Ultrafiltration (UF)/Reverse Osmosis (RO) System for Desalination of Brackish Water and Coastal Seawater

The effectiveness of feed water pretreatment in reverse osmosis (RO) membrane desalination is essential to the operability of RO plants. Feed pre-filtration and chemical treatments (e.g., additives to suppress mineral scaling and reduce biofouling) are key methods to mitigate RO membrane fouling. In recent years, microfiltration (MF) and ultrafiltration (UF) systems have been increasingly explored as a method for effective RO feed pre-filtration. While the concept of MF/UF integration with RO has achieved  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 reducing cost and minimizing environmental impact). In meeting the above challenges, a novel concept of self-adaptive integrated UF-RO operation was developed and field tested.  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  45,000 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 fast changing feed water quality (with respect to natural organic matter concentration, salinity, temperature and RO fouling propensity) by selecting the appropriate UF filtration and backwash strategies. Real-time individual UF module resistance data are utilized in the control algorithm to determine the appropriate inline coagulant dose, 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 reduces substantially system foot print and energy usage.  This system also allows real-time characterization of the fouling mitigation and contaminant removal performance of the UF membranes. Results from extensive field studies for treatment of cooling tower blow down (CTBD) water for reuse and coastal seawater successfully demonstrate 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.