(811c) Novel System and Field Characterization of Self-Adaptive UF-RO Membrane Desalination of Coastal Seawater

Effective feed water pretreatment in reverse osmosis (RO) membrane desalination is essential to ensure optimum performance of RO plants. Microfiltration (MF) and ultrafiltration (UF) systems have been widely used as integral processes of RO feed pretreatment. While the concept of MF/UF integration with RO is appealing and has met with a reasonable level of success, there are still 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 (e.g., coagulants) and membrane cleaning chemicals (for the purpose of both cost reduction and minimizing environmental impact). In meeting the above challenges, a novel approach of self-adaptive UF operation was developed and field demonstrated. Self-adaptive control of coagulant dose and filtration duration was successfully demonstrated in extensive long-term field studies of seawater desalination at the US Naval Base at Port Hueneme California. The present approach to 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. This system is capable of processing up to about 36,000 gallons per day of raw feed water at a maximum recovery of about 36%. Real-time individual UF module resistance and fouling profiles are utilized to determine the appropriate coagulant dose, backwash frequency and intensity as feed water conditions change. Assessment of the impact of various operational parameters including coagulant dose, UF feed and backwash directions and module configurations, backwash source, duration, and flux on UF fouling behavior and permeability recovery was evaluated over a field study period of about a year. Adaptive control of inline coagulation was shown to be essential for effective UF backwash in order to minimize the frequency of chemical cleaning (e.g., effective UF operation without system shutdown and chemical cleaning). Furthermore, coagulation enhanced UF was found to assist in reducing TEP (Transparent Exopolymer Particles) passage through the UF and reduce the propensity for RO membrane fouling. The potential use of the present integrated MF-UF-RO approach for distributed deployment of smart water filtration and desalination systems will be discussed with specific focus on operability and fouling mitigation.