Retrofit of a California coastal desalination plant: add technology, lower costs

California´s largest municipal drinking water seawater desalination facility is located in the city of Marina on Monterey Bay. The plant produces about 1000 m/sup 3//d (/spl sim/300,000 gallons) of potable water in compliance with California primary drinking water standards. Although only seven years old, the plant does not meet the economic needs of the operator in light of the increased electrical costs in California. To take advantage of reduced weekend electricity rates, the plant is operating Thursday through Monday with product water costs about $2.40/m/sup 3/. In 1996-1997, when electricity rates were significant lower, the plant operated seven days a week and product water costs were $1.40/m/sup 3/. By adding several technologies during a retrofit of the facility. Oases is able to lower operating costs by 64%. Key technologies employed include installation of a state-of-the-art pressure exchange system to recover energy, high-efficiency pumps, removal of the plant from local electrical grid and utilizing natural gas fired microturbines with heat recovery. Planned future improvements include incorporation of plasma chemical reactor ozone generation technology for pre-treatment of seawater and wireless SCADA coupled with predictive diagnostic software. The retrofit will allow production of potable water for less than $0.60/m/sup 3/ or about $740 an acre-foot. Without debt service on the original plant, the retrofit costs are only $0.49/m/sup 3/ (about $600 per acre-foot).