Role of fungi in biological ion exchange for treating wastewater: performance and mechanisms under humic acid stress.

The efficient removal of pharmaceuticals and personal care products (PPCPs) in wastewater remains a significant challenge due to their limited degradability in conventional treatment processes and interference of humic acid (HA).Biological ion exchange (BIEX) has emerged as a promising alternative technology, integrating the adsorption capacity of resin with biodegradation capability of attached microorganisms. This work investigated the performance of BIEX system constructed with magnetic polyacrylic resin (NDMP) for removing ibuprofen (IBU) and diclofenac (DCF) under HA stress, benchmarked against systems constructed with commercial A860 resin and high-density polyethylene (HDPE). NDMP system exhibited superior steady-state removal of IBU (100%), dissolved organic carbon (DOC, 70%), and DCF (29%), outperforming A860 and HDPE. While initial removal was dominated by adsorption, long-term stability was sustained by biodegradation, with biological contributions exceeding 63% for DOC and 96% for IBU in NDMP system. NDMP supported greater attached biomass (9.5 vs. 3.3 mg/mL carrier on HDPE) and metabolic activity (2.2 vs. 0.6 μg ATP/mL carrier on HDPE). Crucially, NDMP selectively enriched fungal populations (7.2 vs. 1.1 × 108 copies/g microorganisms). Antifungal assays using amphotericin B quantitatively confirmed that fungi accounted for approximately 20% of IBU removal in NDMP system and 13% of IBU removal in HDPE system, consistent with their level of fungal abundance. Under HA stress, bacterial diversity declined, whereas fungal diversity increased. These findings underscore the advantage of NDMP as BIEX carrier and provide explicit evidence for the role of fungi in PPCPs removal, which has been largely overlooked in previous BIEX research.