Every Last Drop - How Treatment Plant Improvements Maximize Reuse Efficiency

Presentation Description: For 22 years, the Orange County Sanitation District (OC San) and the Orange County Water District (OCWD) have collaborated to enable the Groundwater Replenishment System (GWRS), the world’s largest water purification system for indirect potable reuse. Nearly a decade ago, OCWD initiated the GWRS Final Expansion to produce 130 million gallons per day (mgd) of purified recycled water and support OC San’s goal of maximizing water recycling. OC San operates two major wastewater treatment facilities: Plant No. 1 in Fountain Valley and Plant No. 2 in Huntington Beach.

Previously, the GWRS was fed solely from Plant No. 1 and produced 100 mgd of purified recycled water. This allowed OC San and OCWD to optimize influent water quality, since flows not ideal for purification could be sent to Plant No. 2 for treatment and ocean discharge or non-potable reuse. To facilitate the GWRS Final Expansion, most of the Plant No. 2 flow needed to be directed to the GWRS. However, Plant No. 2 processes “non-reclaimable” industrial flows and would have to be managed through separate treatment than the GWRS-bound flows. Therefore, Plant No. 2 needed the capability to split influent headworks flows into reclaimable and non-reclaimable streams. Achieving this separation while maintaining the reliable operation of the 317-mgd treatment plant was a challenging but critical task. The solution involved implementing a series of measures, including slide gates, stop plates, a 72-inch diversion pipeline, pump replacements, a reclaimable recirculation line to handle low diurnal flows, and rerouting non-reclaimable sidestreams.

The collaborative efforts of OC San and OCWD required innovative solutions to address the challenge of directing influent flows from Plant No. 2 to the GWRS. By physically separating the headworks and implementing various infrastructure modifications, the reliable operation of the treatment plant was ensured while reclaiming as much water as possible. This project stands as a testament to OC San’s commitment of providing a reliable water source for the GWRS.