Amoxicillin removal by pre-denitrification membrane bioreactor (A/OMBR): performance evaluation, degradation by-products, and antibiotic resistant bacteria

Membrane bioreactors (MBRs) are one of the treatment technologies with the potential to remove emergingcompounds from wastewater. The present work evaluated the efficiency of an MBR pilot system in removingamoxicillin from synthetic wastewater using a continuous flow pre-denitrification MBR (A/O-MBR) pilot unit.The system operated in three phases: (1) synthetic wastewater and hydraulic retention time (HRT) of 40 h; (2)adding amoxicillin 100 μg L−1 to the influent, and (3) varying flowrate to HRT of 20 h. Liquid chromatographycoupled to high resolution mass spectrometry analysis confirmed the presence of five amoxicillin degradationby-products in the effluent. The addition of amoxicillin did not affect chemical oxygen demand (COD) or dissolvedorganic carbon (DOC) removal efficiencies. Respirometry showed that amoxicillin level did not inhibitheterotrophic bacteria metabolism. The change in HRT reduced the DOC removal (from 84% to 66%) but did notinfluence COD (> 94%) or total nitrogen (> 72%). The amoxicillin and by-products removal decreased from80% to 54% with HRT change. Adsorption and biodegradation represented the largest removed fraction of theantibiotic in the A/O-MBR system (68%). Ecotoxicity assays showed P. fluorescens was more resistant and E. coliless resistant to amoxicillin residues at effluent sample matrix.