Deciphering functional adaptability of microalgal-bacterial granular sludge under salicylic acid stress

In this study, the impact of salicylic acid (SA), a prevalent non-steroidal anti-inflammatory drug metabolite, on microalgal-bacterial granular sludge (MBGS) systems was systematically investigated. Results demonstrated that the MBGS system exhibited high pollutant removal efficiency in both synthetic and real wastewater containing 1 mg/L SA, achieving 81.6 % organics, 72.3 % nitrogen, and 77.1 % phosphorus removal. This performance was attributed to increased extracellular polymeric substance secretion and the proliferation of stress-tolerant Proteobacteria, Cyanobacteria and Bacteroidota, which helped alleviate SA toxicity. Critically, 1 mg/L SA promoted nitrogen removal through microbial assimilation by modulating the abundance of key functional genes. Further analyses identified SA biodegradation into pyruvic acid and maleic acid, with multiple pathways ultimately entering the tricarboxylic acid cycle. This study confirms the efficacy of MBGS for treating SA-contaminated wastewater and highlights its potential as a sustainable strategy for mitigating pharmaceutical and other emerging contaminants in engineered ecosystems.