Metabolic responses of microalgal-bacterial granular sludge to enrofloxacin and sulfamethoxazole exposure

This study examined the removal performance and responses of the microalgal-bacterial granular sludge (MBGS) system to enrofloxacin (ENR), sulfamethoxazole (SMX), and their combination. Results showed that MBGS could achieve 73.2 % and 64.0 % removals of ENR and SMX at 1 mg/L of mixed antibiotics, while ENR severely affected organics removal (from 84.5 % to 74.7 %). Antibiotic exposures could raise reactive oxygen species levels, thereby disrupted cellular structures and energy metabolism. ENR had the most significant disruptive effect, markedly reducing the abundance of Oscillatoriales and impairing their interactions with other taxa. In contrast, Xanthomonadales and Micrococcales were essential for sustaining energy metabolism under ENR stress, while Hyphomicrobiales demonstrated strong adaptability to these antibiotics. Notably, the combination of ENR and SMX mitigated oxidative stress, facilitating the growth of Rhodospirillales and Chloroflexales. These findings provide insights into microbial adaptation mechanisms under antibiotic pressure and offer guidance for optimizing wastewater treatment strategies in antibiotic-contaminated environments.