Design of a New Membrane Filtration and Reverse Osmosis Treatment System
The city of San Clemente (City) owns and operates a wastewater collection and treatment system within its service area, which includes a Wastewater Reclamation Plant (Plant) that provides wastewater treatment and produces Title 22-compliant recycled water. The Plant currently has excess capacity available for the treatment of wastewater.
The Plant processes include preliminary treatment, primary treatment, activated sludge secondary treatment, and tertiary treatment for recycled water. A portion of the existing secondary-treated wastewater is sent for tertiary treatment to produce unrestricted Title 22 recycled water. The tertiary recycled water contains excessive total dissolved solids (TDS) of approximately 1500 mg/L, which is above the permitted limit of 1,100 mg/l and results in end-user irrigation challenges. The average capacity of the tertiary system is 4.4 MGD, with a peak capacity of 5 MGD.
Why this project is important
Recycled water use has steadily increased in recent years. Various factors, such as diminishing water supplies, drought, seawater intrusion, and population increase have created an urgency for municipalities and industries to explore alternate water supply options. Microfiltration (MF) and reverse osmosis (RO) are treatment processes that play a vital role in developing water reuse and conserving our water resources.
- MF is a separation process that uses filtration membranes to remove suspended solids, turbidity, and bacteria from the wastewater secondary effluent. MF is necessary prior to RO to clean the secondary effluent to keep the RO membranes from fouling.
- RO is used in advanced water reuse applications where high-quality permeate is required with low TDS and hardness. An RO system uses multiple filtration stages and semi-permeable membranes to filter more than 99.9% of the TDS.
LEE + RO Services
The City contracted LEE + RO to design a MF/RO treatment system to improve the quality of the recycled water. Services include design engineering, bidding support, and engineering services during construction for the design and construction of the new MF/RO treatment system.
The new MF/RO system will treat a portion of the Plant’s secondary effluent to improve the quality of the blended reclaimed water by lowering TDS to an acceptable level (less than 800 mg/l) to meet permit limits. The project will blend 1.2 MGD of MF/RO product water with 2.2 MGD of recycled water for total product water of 3.0 MGD with TDS less than 800 mg/l.
LEE + RO understands the challenges that high TDS poses to many recycled water users in California and the valuable role recycled water usage plays in achieving water reliability and security. This project will allow the City to continue to produce and sell 1 MGD to its existing customers and will also allow the distribution of 2 MGD of recycled water to the Santa Margarita Water District to reduce both agencies’ demands for imported potable water used for irrigation and recreational uses at golf courses and community parks.
