Ciprofloxacin Removal and Antibiotic Resistance Genes Response in the High-rate Anaerobic Membrane-coupled System Treating Swine Wastewater: Performance, Mechanism, and Metagenomics
Antibiotics in swine wastewater are emerging contaminants with low concentrations but significant environmental risks. Their inhibitory effects on biological treatment systems and the proliferation of antibiotic resistance genes have raised widespread public concern. This study designed a high-rate anaerobic membrane-coupled system: an expanded granular sludge bed reactor coupled with anaerobic membrane bioreactor (EGSB-AnMBR) system to treat swine wastewater containing fluoroquinolone antibiotic ciprofloxacin (CIP). Under a volumetric loading rate of 9.6 kg/(m3 d), the EGSB-AnMBR system achieved over 99% chemical oxygen demand (COD) removal efficiency and 36.3% CIP removal efficiency. Mass balance analysis indicated that sludge adsorption served as the primary mechanism for CIP removal, while the microfiltration membrane and its attached biofilm contributed negligibly. 16S rRNA gene high-throughput sequencing revealed that under CIP stress, the abundance of CIP-resistant Spirochaetota increased substantially, whereas Patescibacteria abundance progressively decreased. Metagenomic analysis demonstrated microbes in anaerobic granular sludge (AnGS) achieved "defense-efflux" by activating macB/evgS efflux pumps while suppressing tetA, whereas membrane biofilm (MB) developed a "storage-retention" strategy through synergistic effects of tetA and evgS. The EGSB-AnMBR system exhibits promising application potential for swine wastewater treatment and antibiotic control, providing significant support for livestock pollution management.