Mitigation via physiochemically enhanced primary treatment of antibiotic resistance genes in influent from a municipal wastewater treatment plant

In this study, a combined coagulation-dissolved air flotation (DAF) process was employed as enhanced primary treatment (EPT) to simultaneously reduce eleven ARGs (tetA, tetM, tetQ, tetX, sul1, sul2, qnrD, ermB, bla(TEM), aac (6')-lb-cr, floR), class 1 integrons-integrase gene (intI1) and common pollutants in the influent of a WWTP and then compared to primary sedimentation alone. In the combined coagulation-DAF process, the optimum doses of PACl, FeCl3 and Al-2(SO4)(3) required to achieve a removal efficiency exceeding 90% of total suspended solids (TSS) were 25 mg/L, 75 mg/L and 100 mg/L, respectively. The log removal of all quantified ARGs treated by the combined coagulation-DAF process with the three coagulants exceeded 0.44-log, a higher removal efficiency of ARGs compared to primary sedimentation alone (0.03-log). Among the three coagulants, FeCl3 showed the highest log reduction for targeted ARGs. In addition, the three coagulants showed similar capabilities to non-selectively and modestly decrease most ARGs. Most ARGs and intl1 demonstrated strongly negative correlations with the removal efficiencies of physicochemical parameters in the treated wastewater, implying that co-removal of colloidal matter, solids, phosphate, ammonium and organic matter played a crucial role in reduction of ARGs during the combined coagulation-DAF process. Particularly, strong correlations were observed between the reduction of total phosphorus (TP) and ARGs, indicating that TP may provide a suitable proxy for reduction of ARGs in this process. Despite handling influent comprised of ARGs and pollutants of high levels and diverse types, the combined coagulation-DAF process led to improved removal of ARGs along with colloidal substances. Thus, the results demonstrate the potential of a combined coagulation-DAF process to reduce ARGs flowing into WWTPs.