Changing Tides: Innovative Membrane Design for Desalinating Waters with Tidally Fluctuating Water Quality in Northern California

摘要

East Bay Municipal Utilities District (EBMUD), Contra Costa Water District (CCWD), San Francisco Public Utilities Commission (SFPUC), and Santa Clara Valley Water District (SCVWD) are joining forces to investigate desalination as a potential regional solution to water supply reliability. To enhance their dry year supplies, the Partner Agencies are conducting studies that could result in one or more regional desalination facilities with an ultimate total capacity of up to 71-mgd in Northern California. One of the challenges for this project is unique water quality. The site selected for pilot testing is the estuarine junction of the San Francisco Bay and its freshwater tributaries, where raw water salinity can fluctuate by an order of magnitude on a tidal and seasonal basis. Traditional membrane technologies for desalination have been developed to treat either brackish water or seawater. These coarse classifications can be applied when raw water quality can be categorized as one or the other, but are less readily applicable in surface waters with significant tidal influence. In order to address fluctuating water quality with the available suite of membrane technologies, several innovative design approaches have been selected for pilot testing. Three desalination trains are being operated in parallel, integrating a variety of membrane type configurations including NF, brackish water, and seawater elements in one-stage and two-stage configurations. The objective of pilot testing is to determine the efficacy of each configuration with respect to feed water quality, process efficiency, and long-term operation. Pilot testing is underway and will continue through early 2009. The side-by-side comparison of three different treatment approaches during this pilot study will generate valuable information for the water industry. Detailed findings are presented to highlight treatment efficiencies and operational experiences in evaluating the performance of various membrane configurations in tidally fluctuating feed water quality.