Unraveling the nexus of Cr (VI), aniline, and microbial ecology on aniline-degrading biosystem: Removal efficiency, sludge type, microbial ecology

[Display omitted] •Cr (Ⅵ) stress had little effect on the degradation performance of aniline, but significantly inhibited nitrogen removal function.•Nitrification performance recovered spontaneously when Cr (Ⅵ) concentration was below 5 mg/L, while denitrification performance was severely impaired.•Cr (Ⅵ) had a decreasing and quenching effect on EPS and its fluorescent substances.•The abundance of nitrifiers and denitrifiers in the Cr (Ⅵ) system was significantly lower than that Cr (Ⅵ) with none. In order to explore the stress principle of Cr (Ⅵ) on aniline biodegradation system, a control group and experimental groups with the concentration of Cr (Ⅵ) at 2, 5, 8 mg/L were set up. The results demonstrated that Cr (Ⅵ) had minimal effects on the degradation efficiency of aniline but significantly inhibited nitrogen removal function. When Cr (Ⅵ) concentration was below 5 mg/L, the nitrification performance recovered spontaneously, while denitrification performance was severely impaired. Furthermore, the secretion of extracellular polymeric substances (EPS) and its fluorescence substance concentration were strongly inhibited with increasing Cr (Ⅵ) concentration. High-throughput sequencing revealed that the experimental groups were enriched with Leucobacter and Cr (Ⅵ)-reducing bacteria, but the abundance of nitrifiers and denitrifiers was significantly decreased compared to the control group. Overall, the effects of Cr (Ⅵ) stress at different concentrations on nitrogen removal performance were more significant than those on aniline degradation.