Is the Juice Worth the Squeeze? Evaluating of the Relevancy of High Recovery RO from a Municipal Water Supply Perspective

New Facility Trends More Needs for In-Land Brackish RO (groundwater and surface water) More RO Use in Potable Reuse Applications RO for PFAS Removal Many of the above applications are targeting high RO recovery rates Albert Robles Center – Advanced Water Treatment Plant, Water Replenishment District of Southern California RO operations, much like life, is a balancing act Process Goals Operational Trade-Offs Optimize Recovery Risk of Over-Recovery (scaling) Prevent Fouling and Scaling Reduce Recovery or Flux Rate Optimize Salt Rejection Increase Flux Rate and Energy Extend Membrane Life Operate in “Safe Zone” Optimize Energy and Sacrifice Water Quality or Chemical Use Recovery Rate These goals are good, but we must choose which goals to prioritize. We can’t have them all!!! High Recovery Operations More salts passing to the permeate side of membrane Higher operating pressures (increased safety concerns) Increased energy use (marginal impact) Higher TDS in RO concentrate Increased CAPEX and OPEX Possible concentrate scaling / disposal concerns Potential Domino Effect Increasing recovery too much may result in negative impacts to plant operations Increased Concentration Factor = Increased Scaling Potential (possible DIW plugging) More Frequent Membrane Cleaning Decreased Membrane Life Increased Cleaning Chemical Use and Operational Labor Evaluating New Technologies Criteria: Operational Flexibility Concentrate Enhanced High-Efficiency Reverse Flow Reversal Reverse Job-Place Safety Recovery Reverse Osmosis Osmosis (HERO) Osmosis (FRRO) (CERRO) Ease of Maintenance Energy Use Product Water Quality System Complexity Closed Circuit Reverse RO Infinity (ROI) Impact RO Osmosis (CCRO) Performance Warranties Reliability Already Used Full-scale High Recovery Reverse Electrochemical Nano MAXH2O Pulse Flow RO and Osmosis (HIROX) Diffusion (END) MAXH2O Desalter Conventional 3-Stage Design Drawbacks Permeate recovery, capacity, and quality are typically fixed values Membrane Cleaning Limitations: Must take entire train (skid) offline to clean 3rd Stage (significant capacity loss) Difficulty Achieving Flux Balance: 3rd Stage membranes are normally underutilized (1st and 2nd Stages are most productive) 25 Permeate Flux Balancing Flux balancing is recommended for best case performance of RO membranes to avoid: Excessive flux rates in lead Stage 1 elements impacts membrane element lifespan Poor permeate quantity and quality in subsequent stages Common Flux Balancing Methods: Permeate Throttling (Backpressure) Hybrid Membrane Elements Interstage Boost (Pump) Interstage Boost (Turbocharger) Stage RO with Flux Balancing 4:2: Membrane Array Permeate Stage Membrane Array Stage Membrane Array M Stage Pretreatment Membrane Array High Pressure Pump M Concentrate Booster Pump M Booster Pump.