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City of San Diego Brine Minimization

City of San Diego Water Department

In order to diversify its potable water supply portfolio, the City conducted a 12-month San Pasqual Brackish Groundwater Desalination Demonstration Project, which was was aimed at determining the plant operational parameters. The demonstration plant operated at 85% recovery and generated more than 22 gpm of brine, which was directed towards an existing sewer for disposal at the Hale Avenue Resource Recovery Facility. However, recognizing the potential environmental, political, institutional and technical challenges of employing this method of brine management for a large scale plant, the City investigated means of minimizing the brine flow. The goal of the Brine Minimization Project was to assist the City in developing non-thermal brine treatment alternatives, in addition to the salt-tolerant plant marshes already being investigated. This project investigated precipitative softening processes using two promising technologies (tubular membrane filtered lime slurry reactors and pellet reactors) and a biological reducing process to eliminate oxyanions (e.g., sulfate, nitrate). The overall treatment train objectives were to minimize the total brine volume and the mass of salt contained in this brine without using any cost-prohibitive thermal processes currently incorporated in treatment schemes that approach the recoveries described here (i.e., near to complete zero liquid discharge).