Insights into the response of nitrogen metabolism to sulfamethoxazole contamination in constructed wetlands with varied substrates

This study conducted an analysis of the variations in nitrogen metabolism pathways within constructed wetlands (CWs) using zeolite (CW-Z), ceramsite (CW-C), and lava (CW-L) under high concentration sulfamethoxazole (SMX) stress. The introduction of SMX hindered the formation of hydrogen bonds on the substrate surfaces; however, these surfaces still maintained a dense and thick biofilm. CW-Z exhibited superior removal efficiencies for ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) compared to CW-C and CW-L, with removal rates of 92.54 +/- 2.88 % and 89.39 +/- 6.74 %, respectively. Interestingly, the proportion of genes involved in nitrification, denitrification and nitrate reduction genes in CW-C (36.05 %) were higher than that in CW-C (29.81 %) and CW-L (29.70 %) but the interactions among nitrogen functional bacteria in CW-Z were much more complex. Further analysis of the nitrogen metabolism pathway indicated that under CW-Z enhanced dissimilatory nitrate reduction SMX stress, while CW-L enhanced assimilatory nitrate reduction process compared to CW-C.