Understanding the impacts of operation mode sequences on the biological aniline degradation system: Startup phase, pollutants removal rules and microbial response

[Display omitted] •Four reactors all achieved efficient aniline degradation and nitrification.•Anaerobic aniline degradation could be evolved with the operation of the reactors.•Operation mode sequences controlled the system-dominated denitrification pattern.•O/AX mode best fitted for the demands of aniline and simultaneous nitrogen removal. Comparative evaluation of SBRs under different modes (AX/O, AN/AX/O, AN/O/AX, O/AX) with same aniline wastewater arrangements, presenting the startup and performance differences of reactors. The results revealed that the four systems realized the efficient aniline and NH4+-N removal on the basis of sufficient aerobic time. Anaerobic aniline degradation was also achieved in the first three reactors after acclimation. The denitrification efficiency was the highest in O/AX reactor and the lowest in AN/O/AX due to mode sequence setup. Pollutants variations in the typical cycles experimental data combined with microbial diversity analysis were highlighted that aerobic denitrification contributed the most under O/AX mode, while the other three modes relied on anoxic denitrification. Meanwhile, low nitrifiers and aerobic denitrifiers abundance might be another reason for the poor denitrification of AN/O/AX mode. It was inferred that denitrification was most susceptible to operation mode sequences.