Ciprofloxacin and sulfamethoxazole biotransformation products in anaerobic packed bed biofilm reactor applied to the sanitary sewage treatment

The presence of antibiotics in the environment has received a lot of attention in recent years due to their ability to promote and spread antimicrobial resistance. In this work, the biodegradation of the antibiotics ciprofloxacin (CIP) and sulfamethoxazole (SMX), as well as the concurrently generation of their biotransformation products (BTPs) were assessed in an anaerobic packed bed biofilm reactor (APBBR) treating sanitary sewage. Initially, anaerobic batch assays at high concentrations of the antibiotics (5 mg L-1) were performed to identify the metabolites generated during the CIP and SMX biodegradation in methanogenic condition. From the mass transitions (m/z) of the identified BTPs, they were analyzed along the spatial profile of the APBBR fed with sewage (300 ngCIP L-1 and 400 ngSMX L-1 approximately). Three BTPs were identified: one related to the biodegradation of CIP (m/z 316) and two related to the biodegradation of SMX (m/z 256 and m/z 270). The molecular structures of the BTPs revealed that the biotransformation occurs mainly in the isoxazole ring of SMX and there was a dehydroxylation in the CIP molecule. Nonetheless, the sulfonamide and fluoroquinolone molecular structures remained intact in the anaerobic effluent stream, thus presenting residual antimicrobial activity in the environment.