70 MGD Indirect Potable Reuse: Optimization of Orange County's Groundwater Replenishment System

Currently in commissioning and testing and planned for operation in late 2007, the Groundwater Replenishment (GWR) System in Fountain Valley, California is jointly sponsored by Orange County Water District (OCWD) and the Orange County Sanitation District (OCSD). It is an indirect potable reuse project that will initially produce 70 million gallons per day (mgd) of highly treated recycled water for groundwater recharge. The system will treat clarified secondary effluent, currently discharged into the ocean, using microfiltration (MF), reverse osmosis (RO), and advanced oxidation (ultraviolet light treatment with hydrogen peroxide).It was determined early in the project planning phase that the small-scale pilot research and performance demonstration testing would best be verified and optimized by operation of a 5 mgd process during construction of the full-scale facility, utilizing existing RO facilities at the Water Factory 21. Operation of this Phase I plant included verification of expected product flows and quality, while establishing maintenance durations, reliability, chemical feed and power requirements. Additionally, the wastewater treatment operations were continually analyzed and controlled to produce acceptable flows for such high levels of treatment. Each of these operational aspects was studied to enhance the economic viability of the GWR System.The 5 mgd plant operated from June 2004 to August 2006, and consisted of submerged MF equipment located in temporary tankage, a polyamide RO membrane system designed into modified Factory 21 facilities and a completely new UV disinfection unit. Each process component was fitted with associated chemical feed systems including MF pretreatment of sodium hypochlorite for chloramine formation, citric acid and sodium hydroxide for MF cleaning cycles, sulfuric acid and threshold inhibitor for RO scale control and hydrogen peroxide for advanced oxidation activation prior to the UV unit.