Strategy for repurposing waste anion exchange resins to construct a biofilter for removing dissolved organic matter: performance and mechanism

Anion exchange resins are widely employed in wastewater and drinking water treatment plants to remove dissolved organic matter (DOM). However, the degradation of resin performance necessitates the discontinuation of these treatment projects, resulting in the idling of underperforming resins, referred to as waste anion exchange resins (WAER). Given the substantial investment in operational costs, determining how to economically utilize WAER is essential for restarting the treatment projects. Therefore, this study proposed a strategy for repurposing WAER to construct a biofilter for DOM removal. A biofilter, termed biological anion exchange resin (BAER), was developed using WAER and compared with two conventional biofilters: biological activated carbon (BAC) and sand filter. After the acclimatization period, the BAER biofilter achieved a removal of up to 21.42 % of dissolved organic carbon (DOC), which is 5.8 times greater than the removal rate of the sand filter and comparable to the BAC. Notably, BAER exhibited the highest removal rate of aromatics, achieving 41.04 % UV₂₅₄ removal, which are precursors to disinfection byproducts (DBPs). Consequently, BAER demonstrated superior control of DBPs, with a removal efficiency of 39.59 %. Additionally, BAER demonstrated effective removal of humic substances due to the bioregeneration of its adsorption sites, which led to significant differences in both the structural composition and functional expression of the biological community in BAER compared to other biofilters. This study also revealed that the bioregenerated adsorption sites primarily capture DOM through electrostatic attraction rather than ion exchange. Overall, these findings confirm the promising application of the BAER biofilter constructed with WAER and offer valuable insights into the associated removal processes.