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Impact of wastewater treatment plants on dissemination of antibiotic resistance genes

Küçükünsal, Serkan
Wastewater treatment plants (WWTPs) as hotspots of the antibiotic resistance genes (ARGs) pose risk to receiving environments. Removal of ARGs through WWTPs, therefore, is great importance. For this reason, common types of WWTPs including conventional activated sludge (CAS), biological nutrient removal (BNR), sequencing batch reactor (SBR), membrane bioreactor (MBR), package MBR, WWTP with coagulation-flocculation and UV disinfection units were investigated in terms of their seasonal removal efficiencies on seven ARGs including the genes blaCTX-M, sul1, tetA, aadA, ermB, qnrS and cmlA corresponding to commonly used antibiotics β-lactams, sulfonamides - trimethoprim, tetracyclines, aminoglycosides, macrolides – lincosamides - streptogramins, quinolones and amphenicols, respectively. Copy numbers of the ARGs and overall bacterial genes in both influents and effluents of the each WWTP were determined through quantitative polymerase chain reaction. The highest ARG removal efficiencies were obtained from MBR and package MBR systems. Significant seasonal variations were observed in the CAS and BNR systems (p<0.05). The lowest log reductions were determined in both autumn and winter for CAS and in summer for BNR systems. The abundance of the overall bacterial genes were elevated in the sludge of CAS system. Similarities in the removal efficiencies of all WWTPs tested on both overall genes and ARGs indicated that removal mechanism was not ARG specific.