Design considerations for biological ion exchange drinking water filters: Resin selection, backwash, and regenerations

Two pilot studies provide insights into the design and operations of biological ion exchange (BIEX) drinking water filters. A lab-scale pilot with strong-base anionic (SBA) and weak-base anionic (WBA) resins demonstrated 35% and 31% removal of dissolved organic carbon (DOC) up to 30 months, until secondary ion exchange exhaustion. While the WBA resins exhibited 14% less removal of DOC, their larger capacity doubled the duration until filter exhaustion. WBA filters were less affected than their SBA counterparts by sulfate-containing inlet waters. In a second pilot, while water with high DOC yielded rapid exhaustion of SBA resins, air scouring increased the breakup of filter media and improved solids removal by 30× compared to hydraulic backwash alone. Significantly, DOC removal improved by 36% for a week following air scour. Key recommendations include the use of WBA resins to extend operating life while implementing air scouring can dramatically improve short-term DOC removal.