Is an Extended RO Membrane Warranty Worth it?

Background Reverse Osmosis Membranes have been used in wastewater since ~ OCWD Water Factory 21 – 1976 The change to Thin Film Composite Membranes and Microfiltration/ Ultrafiltration began in 1991 Success of large-scale facilities such as OCWD GWRS has led to numerous other facilities being planned or constructed Background OCWD – GWRS System: Reverse Osmosis 5mgd RO Unit design  2007 Original 15 units  2015 Additional 6 units  2023 Additional 6 units 3 stage design (78:48: A-E) or (77:49: F-I)  Stage 1 split for CIP  7 elements per vessel  Interstage Booster added to address higher salinity in 2023 RO Element Facts “They are like children” – Bill Dunivin  6 different elements from 4 different suppliers  28,350 membranes installed (27×1050)  >66,000 membranes placed in service since 2007 Limitations of Standard Warranties Limitations of Supplier Language Cleaning Commentary  Suppliers recommend cleaning  In wastewater this occurs within membranes on a 10-15% loss of a matter of days, and would permeability (20-30% for “high result in near constant cleaning. fouling” water) “Oh you mean stabilized permeability”  In wastewater, we have  “If normalized permeability drops successfully seen membrane 30-50%, it may be impossible to operate greater than 50% loss of fully restore performance back to permeability baseline conditions”. Deposits build up on the membrane surfaces during operation until they cause loss in normalized permeate flow, loss of normalized salt rejection or both. Elements should be cleaned when one or more of the below mentioned parameters are applicable:  Normalized permeate flow drops 10%  Normalized salt passage increases 5-10%  Normalized pressure drop (feed pressure minus concentrate pressure) increases 10-15% If you waited too long, cleaning may not be restore the membrane element performance successfully. Limitations of Standard Warranties Cleaning Requirements In normal operation, the membrane in reverse osmosis elements can become fouled by mineral scale, biological matter, colloidal particles and insoluble organic constituents. Reality Check RO works great; membranes can last 5-8 years when properly operated and cleaned Wastewater is an inherently “high fouling” environment (5 -15mg/L TOC) The factory wet test data has nominal value Pure salt solution made up with RO permeate Tested at flux rate of about 2x the design of a system Projection programs pressure/removal can be misleading (varies by supplier) Normalization of data and cleaning when required are keys to success RO elements have limited ability to be cleaned and frequent cleaning shortens membrane life. Custom RO Membrane Warranties Typically generated by Engineer Removes “gotcha” language contained in supplier warranties Allows use of RO membrane in a wastewater Specify manufacturer’s productivity and salt rejection requirements (lot vs. element) Yes there can be inappropriate terms included Point of “Starting Negotiations” Suppliers have attempted to replace custom warranty with the supplier warranties after the selection (supersedes).