Meeting a Growing Need
The Orange County Water District (OCWD) of Fountain Valley, Calif., needed to increase its potable water supplies to meet the future water demands of this fast-growing area. OCWD supplies potable water to approximately 2 million people, and this population is expected to increase to almost three million by 2020.
In 1997, the OCWD and the Orange County Sanitation District released a joint report proposing a groundwater replenishment project (GWRS) to serve the residents of Orange County.
The Orange County Water District Membrane Building.
The project would be environmentally and economically beneficial to the residents of Orange County. Reclaiming secondary treated wastewater would consume only 50% of the energy to import water from Northern California and 66% of the energy costs from the Colorado River, reducing the amount of wastewater discharged to the ocean and providing a new local water source. It would also improve the overall water quality in the groundwater basin by reducing the mineral content as well as preventing ocean water contamination.
Designed to be built in three phases over twenty years, at a cost of $400 million to $450 million, the GWRS will provide as much as 130 mgd of treated reclaimed water when it is completed.
The OCWD has started up an advanced water treatment facility to provide 75 million gal per day (mgd) of reclaimed water for agricultural, industrial and in direct potable use. Part of the GWRS, the water treatment facility consists of a MEMCOR submerged membrane system from Siemens that supplies 87 mgd of water to a reverse osmosis (RO) unit, followed by advanced oxidation (ultraviolet light plus hydrogen peroxide).
Orange County awarded the $27 million microfiltration contract to Siemens in 2002 after extensive pilot and demonstration-scale testing of equipment from three membrane suppliers at OCWD’s previous 5-mgd reclamation plant at the site, known as Water Factory-21. Orange County chose Siemens based on a lifecycle cost analysis of the MEMCOR submerged membrane system. The system is currently the largest in the Americas and one of the largest in the world.
Each train has a dedicated service access platform to facilitate maintenance.
Secondary treated wastewater that was formerly discharged to the ocean is treated with the submerged membrane system to remove all suspended solids, bacteria and other harmful contaminants. The water is then pumped into recharge basins or barrier wells, where it is blended with other groundwater, and then travels through the soil, which provides additional natural treatment of the water.
The MEMCOR membrane system is composed of 26 compact units that provide more than five times the treatment capacity of a conventional clarification system housed in the same footprint. It does not require chemical pretreatment except for prechlorination, and requires less maintenance and operator intervention. The high-quality effluent increases the reliability, and reduces the capital and operating costs, of the downstream RO system.
Each of the 26 units, or cells, contains 608 hollow fiber membrane modules. The cells are arranged in four trains, each having a dedicated MemSAP (service access platform) to facilitate system maintenance. Each cell is fitted with its own filtration pump that draws water through the membrane fibers. The modules are arranged in racks, and sit 14 ft below the raw water elevation. This allows the OCWD to make use of the hydraulic gradient, eliminating the need to pump water into the membrane cells.