New insights into nonylphenol's impact on pharmaceutical wastewater treatment by aerobic granular sludge

Abstract Pharmaceutical wastewater has complex components, containing emerging pollutants such as nonylphenol (NP). Aerobic granular sludge (AGS) has application potential in wastewater treatment due to its unique structure and functions, but the mechanism of NP on AGS remains unclear. This study systematically investigated the effects of different NP concentrations on AGS's pollutant removal efficiency, sludge characteristics, microbial community, and metabolic activity. The results showed that NP exerted a threshold effect of low promotion and high inhibition on AGS: 1 mg/L NP enriched functional bacteria such as ammonia‐oxidizing bacteria ( Nitrosomonas ) and denitrifying bacteria ( Pseudomonas ), promoted the secretion of tightly bound extracellular polymeric substances (TB‐EPS), enhanced granule aggregation and settleability, and simultaneously improved COD (average 94.2%) and ammonia nitrogen removal rates (average 94.5%). However, total nitrogen (TN) removal is more sensitive to NP toxicity: at 5 mg/L, the TN removal rate dropped sharply by 10.7% because core nitrogen cycle bacteria are more vulnerable to NP toxicity. At 10 mg/L, the abundance of Nitrospira plummeted to 0.7%, and pollutant‐tolerant bacteria (e.g., Bacillus) expanded to occupy ecological niches, exacerbating the decline in community diversity and metabolic respiration inhibition. High‐concentration NP further destroyed the granule structure, inducing granule fragmentation, imbalance of EPS components, and deterioration of settleability, forming a negative feedback loop of “structural disintegration ‐ functional decline—microbial imbalance—metabolic inhibition.” This work clarifies the critical transition range and multi‐dimensional action mechanism of NP on AGS, providing key theoretical support for the optimization of AGS processes in NP‐containing pharmaceutical wastewater treatment.