Pilot-scale petroleum refinery wastewaters treatment systems: Performance and microbial communities’ analysis

•Petroleum refinery wastewater is poorly treated in CSTR.•Higher performance treatment was achieved in MBR inoculated with the same consortium than CSTR.•Biomass concentration increased rapidly in MBR but declined in the CSTR due to high toxicity.•The MBR presented a higher bacterial abundance and diversity than the CSTR.•Identification of major acclimated bacterial genera in the MBR could explain its high performance treatment.