Effects of ibuprofen and its transformation products on algal-bacterial granular sludge system

Ibuprofen (IBP), a ubiquitous pharmaceutical micropollutant, poses a significant challenge to conventional biological wastewater treatment processes. This study systematically investigated the treatment efficacy and adaptive responses of algal-bacterial granular sludge (ABGS) under IBP-induced stress. During Phase I (0.5-5 mg/L IBP), the ABGS system maintained robust nutrient removal (COD: 81.8 ± 15.1%; NH₄⁺-N: 88.9 ± 11.1%; PO₄^3--P: 84.1 ± 11.6%), exhibiting performance comparable to the non-exposed control. Under an acute 10 mg/L IBP shock during Phase II, the system exhibited strong self-regeneration capacity. After a brief inhibition (e.g., COD removal dropped to 53.1 ± 13.8%), its nutrient removal performance recovered to 70.6-76.4% for COD and 74.8-78.1% for NH₄⁺-N. Physiological analysis revealed a hormetic defense strategy, characterized by enhanced secretion of extracellular polymeric substances (EPS) and initial upregulation of catalase (CAT) activity at 1 mg/L IBP. However, superoxide dismutase (SOD) activity was consistently suppressed, indicating targeted oxidative stress responses. Microbial community succession was pivotal to this adaptation, with a significant enrichment of known IBP-degrading families, including Comamonadaceae (32.7%), Rikenellaceae (29.9%), and Rhodobacteraceae (13.8%). Two primary IBP biodegradation pathways, namely hydroxylation and oxidation, were identified, driven by the synergistic interplay between specific enzymes and extracellular reactive oxygen species (ROS). Furthermore, toxicity assessment confirmed a general detoxification trend, as the acute toxicity of most degradation intermediates was lower than that of the parent IBP. These findings underscore the potential of ABGS as a sustainable technology for mitigating pharmaceutical pollution, highlighting its integrated adaptive strategy encompassing both physicochemical barriers and microbial metabolic adaptation.