Performance and microbial community of a sequencing batch biofilm reactor treating synthetic mariculture wastewater under long-term exposure to norfloxacin

•NFX affected on the COD and nitrogen removal from mariculture wastewater.•NFX inhibited the microbial activities of nitrifier and denitrifying bacteria.•NFX promoted the EPS secretion and affected the chemical composition of EPS.•NFX affected the relative abundance of nitrifier and denitrifying bacteria. The performance and microbial community of a sequencing batch biofilm reactor (SBBR) treating synthetic mariculture wastewater were evaluated under long-term exposure to norfloxacin (NFX) due to the overuse of antibiotics during the mariculture. The COD and NH4+-N removals had no distinct change at 0–6mgL−1 NFX and were inhibited at 6–35mgL−1 NFX. The specific oxygen uptake rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) of the biofilm kept a decreasing tendency with the increase of NFX concentration from 0 to 35mgL−1. The presence of NFX promoted the microorganisms to secrete more extracellular polymeric substances (EPS) and affected the chemical compositions of EPS. The microbial richness and diversity showed some obvious variations at different NFX concentrations. The present results demonstrated that NFX inhibited the SBBR performance and should decrease the NFX dosage in the mariculture.