Removal of antibiotics and antibiotic resistance genes from domestic wastewater using mesocosm-scale constructed wetlands with different filter media

This study aims to investigate the removal of antibiotics and antibiotic resistance genes (ARGs) in raw domestic wastewater by various mesocosm-scale constructed wetlands (CWs) with different filter media types. These included CW1 with gravel media, CW2 with biochar media and CW3 with zeolite media. The plant of choice in the wetland was Typha latifolia and the reactor was run for 12 cycles with each cycle running for 7 days after which new influent sample was fed. Antibiotic residues (ciprofloxacin and cefixime) concentration was analyzed by HPLC method. The removal of antibiotic resistant genes including qnrs, sul1, dfr1, blaTEM, blaCTXM, blaOXA and 16 S rDNA (indicator of total bacterial biomass) were analyzed by qPCR method at varying hydraulic retention time of 3 and 7 days. The conventional pollutants (nutrients and organic) were removed with a similar removal efficiency from the three CWs. The removal efficiencies of the biochar- and zeolite-layered wetlands had higher removal efficiencies for both antibiotics compared to wetland with gravel media. The CT means reflected the increased removal efficiency of genes by the CWs in the order of blaOXA > blaCTXM > sul1 > blaTEM > qnrS > dfr1 > 16 S rDNA. The reduction in concentrations of qnrS and blaCTXM genes differed significantly across the reactors depending upon filter media types while reduction in concentrations of qnrs and sul1 was significantly different under varying HRTs. Correlation analysis suggested the removal efficiency of ARGs to be significantly associated with total antibiotic concentration (p = 0.012) and total bacterial biomass (p < 0.001). The CW with zeolite as filter media and HRT of 7 days was opted as the best choice for contaminant removal. The findings from this study suggest that constructed wetlands are a promising treatment technology for removing emerging contaminants such as antibiotics and ARGs in domestic wastewater.