Degradation of fluoroquinolones in rural domestic wastewater by vertical flow constructed wetlands and ecological risks assessment

Fluoroquinolones (FQs) are new environmental pollutants in rural domestic wastewater and vertical flow constructed wetlands (VFCWs) are widely used to treat rural domestic wastewater. However, studies on degradation products of FQs by VFCWs and ecological risks assessment have been very limited so far. The degradation of FQs by VFCWs under different hydraulic loads was investigated in this study. The results showed all VFCWs had high removal efficiencies of FQs under either high hydraulic load (above 80%) or low hydraulic load (above 95%). Only one degradation product of FQs was detected and the ecotoxicity declined significantly under low hydraulic load. Six degradation products of FQs were detected and the ecotoxicity had also been reduced in general under high hydraulic load. Cytochrome P450 and enzymes with acetyl transfer activity were directly related to the degradation of FQs. The most dominant ARGs in this experiment was qnrD and the relative abundance of qnrD in effluent of device-A, device-B, device-C and device-D were 93.0%, 94.4%, 85.6% and 89.0% lower than that in influent. Flavobacterium, Microbacterium, Dechloromonas, etc. were the key microorganisms for biological removal of FQs by VFCWs.