Partial nitritation-Anammox (PN/A) process has been recognized as a sustainable process for biological nitrogen removal. Although various antibiotics have been ubiquitously detected in influent of wastewater treatment plants, little is known whether functional microorganisms in the PN/A process are capable of biodegrading antibiotics. This study aimed to investigate simultaneous nitrogen and antibiotic removal in a lab-scale one-stage PN/A system treating synthetic wastewater containing a

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... -used antibiotic, sulfadiazine (SDZ). Results showed that maximum total nitrogen (TN) removal efficiency of 86.1% and SDZ removal efficiency of 95.1% could be achieved when treating 5 mg/L SDZ under DO conditions of 0.5-0.6 mg/L. Compared to anammox bacteria, ammonia-oxidizing bacteria (AOB) made a major contribution to SDZ degradation through their cometabolic pathway. A strong correlation between amoA gene and SDZ removal efficiency was found (p < 0.01). In addition, the degradation products of SDZ did not exhibit any inhibitory effects on Escherichia coli. The findings suggest that it is promising to apply the PN/A process to simultaneously remove antibiotics and nitrogen from contaminated wastewater.