Biological ion exchange as an alternative to biological activated carbon for natural organic matter removal: Impact of temperature and empty bed contact time (EBCT)

Abstract

Biofiltration is a widely used process in drinking water treatment plants to remove natural organic matter (NOM). A novel biofiltration process using ion exchange resins as supporting media (i.e., biological ion exchange or BIEX) has been demonstrated to provide a superior performance compared to conventional biological activated carbon (BAC). In order to optimize the performance of BIEX filters, the impact of temperature and empty bed contact time (EBCT) on NOM removal was systematically studied. In the present study, bench-scale BIEX filters were set up in parallel with BAC filters and operated at different temperatures (i.e., 4 °C, 10 °C and 20 °C) and EBCTs (i.e., 7.5 min, 15 min and 30 min). Higher average dissolved organic carbon (DOC) removal was achieved in BIEX filters (73 ± 6%) than BAC filters (22 ± 9%) at the steady state with an EBCT of 30 min. Higher temperatures improved NOM removal in both BAC and BIEX filters, with the impact being greater at lower EBCTs (i.e., 7.5 min and 15 min). Higher EBCTs could also improve NOM removal, with the impact being greater at lower temperatures (i.e., 4 °C and 10 °C). DOC removal for BIEX and BAC filters can be modeled with a first-order kinetic model (R² = 0.93-0.99). BAC had a higher temperature activity coefficient than BIEX (1.0675 vs. 1.0429), indicating that temperature has a greater impact on BAC filtration than BIEX filtration. Overall, temperature and EBCT must be considered simultaneously for biofilters to efficiently remove NOM.

Keywords: Biological activated carbon (BAC); Biological ion exchange (BIEX); Empty bed contact time (EBCT); Kinetics; Natural organic matter (NOM); Temperature.