Bacterial structure of aerobic granules is determined by aeration mode and nitrogen load in the reactor cycle

•Aeration mode and N load determined the bacterial structure of the aerobic granules.•Supernatant was treated most efficiently in the reactor with the longest anoxia.•Anoxic phases in the reactor cycle promoted heterotrophic nitrification.•Bacteria in granules were more evenly distributed among taxa under constant aeration.•P. aminophilus predominated with 1 anoxic phase/cycle, and Corynebacterium sp. with 2.

This study investigated how the microbial composition of biomass and kinetics of nitrogen conversions in aerobic granular reactors treating high-ammonium supernatant depended on nitrogen load and the number of anoxic phases in the cycle.Excellent ammonium removal and predomination of full nitrification was observed in the reactors operated at 1.1 kg TKN m−3 d−1 and with anoxic phases in the cycle. In all reactors, Proteobacteria and Actinobacteria predominated, comprising between 90.14% and 98.59% of OTUs. Extracellular polymeric substances-producing bacteria, such as Rhodocyclales, Xanthomonadaceae, Sphingomonadales and Rhizobiales, were identified in biomass from all reactors, though in different proportions. Under constant aeration, bacteria capable of autotrophic nitrification were found in granules, whereas under variable aeration heterotrophic nitrifiers such as Pseudomonas sp. and Paracoccus sp. were identified. Constant aeration promoted more even bacteria distribution among taxa; with 1 anoxic phase, Paracoccus aminophilus predominated (62.73% of OTUs); with 2 phases, Corynebacterium sp. predominated (65.10% of OTUs).