BOOK OF ABSTRACTS 109 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL51 Optimizing Biological Ion Exchange for NOM Removal: Backwashing and Regeneration William Chen1, Madjid Mohseni1* 1 University of British Columbia, Chemical and Biological Engineering, 2360 East Mall, Vancouver, BC, Canada, V6T1Z3, madjid.mohseni@ubc.ca * Presenting and corresponding author Biological ion exchange (BIEX) describes extended operation of anion exchange filters with infrequent regeneration to achieve natural organic matter (NOM) removal with reduced maintenance and waste disposal burden. Following from previous work that has confirmed feasibility and elucidated mechanisms of removal [1-4], the present study reports on recent efforts to further optimize BIEX operation through improving backwashing and regeneration efficiency. Air scour is a well-established cleaning procedure in media filtration but has not been rigorously studied in BIEX. Air scour versus water-only backwashing was compared as part of a 16-month field BIEX pilot (70 L bed volume). The addition of an air scouring step (30 psi, 1 BV/min, 20 min) achieved 30x total suspended solids removal (TSS) compared to water-only backwashing. This enhanced cleaning resulted in a 30% increase in dissolved organic carbon (DOC) removal for a week following backwashing, together with increased sulphate release suggesting enhanced secondary ion exchange (sulphate-NOM). Considering that BIEX operation accumulates more biofilm than conventional IEX, these results indicate the importance of biofilm control through vigorous cleaning to improve diffusion to active sites. This also confirms previous results identifying secondary ion exchange—as opposed to biological processes—as the main contributor of NOM removal in extended BIEX operation [3,4]. BIEX eventually needs to be regenerated and this presents a burden especially for small and remote communities. For coastal communities, seawater may be an environmentallyfriendly regenerant. Hence, lab-scale regeneration was conducted with raw seawater (2.6wt% NaCl, 18 mg/L DOC) versus seawater spiked to manufacturerspecified concentrations (10wt% NaCl). Batch jar testing determined similar rate of DOC desorption (pseudo-second order constant), but greater extent of DOC desorption at equilibrium using 10wt% spiked seawater. Nonetheless, comparable DOC removal efficiency was achieved post-regeneration, confirming the viability of raw seawater to restore performance with the limitation that more frequent regenerations are necessary due to incomplete DOC desorption.
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