Effect of ibuprofen on the sulfur autotrophic denitrification process and microbial toxic response mechanism

•The effect of low and high IBU concentrations on SAD process was studied.•Microbial toxic response mechanisms of IBU were proposed from the hormesis effect.•IBU induced different levels of oxidative stress during the SAD process.•IBU affected electron transfer efficiency and microbial metabolic activity.•Heterotrophic bacteria occupied the niche of autotrophic bacteria to IBU exposure.