RO Pilot Testing using Preformed Chloramines to Mitigate Loss in Salt Passage and Trihalomethane Formation

Bureau of Reclamation Kaitlyn Chin Nicholas Babcock Aviv Kolakovsky Elise Chen Tim Dinh Ben Christensen Acknowledgements Trussell Project Team City of San Diego Public Utilities Joseph Quicho, Alice Altes, Michael Violante Aleks Pisarenko U.S. Reverse Osmosis and Chloramines RO membranes are required for certain potable reuse applications CA: Surface Water Augmentation (SWA) and Groundwater Replenishment Chloramines are used to control biological fouling 1. Premature oxidation of RO membranes via the formation and exposure to bromamines and hypobromous acid Testing Setup 3-train RO Pilot (8-inch elements) RO concentrate as feedwater 75-79% recovery, 89-91% with pilot Higher bromide (1000-1400 µg/L) Parallel testing of chloramine strategies Preformed chloramines vs conventional chloramines Demo Permeat Preformed e Chloramine Holding Tank Test Run Membrane A (Overview) Convetional chloramines: up to 3.5x more BDCM up to 15x more CDBM increased salt passage Parameter Median Pilot Feed TDS 4200 mg/L Ammonia 0.12 mg/L as N Nitrate 64 mg/L as N Bromide 1300 µg/L TOC 20 mg/L Test Run Membrane A (THMs) Convetional chloramines: up to 3.5x more BDCM up to 15x more CDBM increased salt passage Parameter Median Pilot Feed TDS 4200 mg/L Ammonia 0.12 mg/L as N Nitrate 64 mg/L as N Bromide 1300 µg/L TOC 20 mg/L Test Run Membrane B (Overview) Convetional chloramines: up to 3x more BDCM up to 11x more CDBM similar salt passage Parameter Median Pilot Feed TDS 4200 mg/L Ammonia 0.11 mg/L as N Nitrate 79 mg/L as N Bromide 1400 µg/L TOC 19 mg/L Test Run Membrane A & C Convetional chloramines: up to 6x more BDCM up to 3x more CDBM exacerbated with longer NaOCl exposure similar salt passage Parameter Median Pilot Feed TDS 4100 mg/L Ammonia 0.10 mg/L as N Nitrate 58 mg/L as N Bromide 1000 µg/L TOC 23 mg/L Key Observations and Takeaways  Greater formation of brominated THMs (BDCM and CDBM) using conventional chloramines Decrease in rejection over time increased permeate concentration of THMs Longer chlorine exposure time increased THM formation Preformed chloramines formed significantly less THMs  First test run showed evidence of premature increase in salt passage vs preformed  All conventional chloramines showed presence of bromine on membrane surface via XPS and positive Fujiwara  Modeled Combined RO permeate THM concentration projected to be below CTR limits  Two SWA potable reuse projects in San Diego County will implement preformed chloramines to control THM formation for CTR compliance.