Impact of industrial wastewater on the dynamics of antibiotic resistance genes in a full-scale urban wastewater treatment plant

Urban Wastewater Treatment Plants (UWTPs) treating mixed urban sewage and industrial wastewater are among the major hotspots for the spread of Antibiotic Resistance Genes (ARGs) into the environment. This study addresses the impact of the wastewater origin on ARG dynamics in a full-scale UWTP (15,000 Population Equivalent, PE) by operating the plant with and without industrial wastewater. Composite samples (4 L) from different treatment points were characterized for their chemical composition, bacterial abundance and for the abundance of four resistance genes against tetracycline, sulfonamides, erythromycin, and quinolones (tetA, sul2, ermB, and qnrS), and of the class 1 integrons (intI1). Although the chemical composition of the outflow significantly differed when the plant operated with or without industrial wastewater, the system efficiency in the removal of bacterial cells, ARGs, and intI1 was constant. The final disinfection by peracetic acid (PAA) did not affect the removal of ARGs, independently of the wastewater origin and the chemical characteristics of the inflows. Our results demonstrated that a well-functioning small size UWTP could treat a significant amount of industrial wastewater mixed in the urban sewage without affecting the overall ARGs and class 1 integrons released into the environment.