Significance of Rhodocyclaceae for the formation of aerobic granular sludge biofilms and nutrient removal from wastewater

The competition of two Rhodocyclaceae-affiliated bacterial populations was assessed during the formation and maturation of aerobic granular sludge in two different types of anaerobic-aerobic sequencing batch reactors. Zoogloea spp. (57%) were predominant in the bacterial community of aerobic granules cultivated in a 2.5-L bubble-column SBR under wash-out conditions selecting for a fast-settling biomass. Zoogloea spp. were favored over “Candidatus Accumulibacter phosphatis” relatives by high transient biomass specific organic loads leaking into the aeration phases. Accumulibacter proliferation over Zoogloea spp. and enhanced dephosphatation were observed after 80 days, as soon as the granular sludge concentration (>7 gVSS•L-1) and the sludge blanket (>30 cm) were sufficiently high to ensure full anaerobic carbon uptake. Formation of up to 2-mm granular aggregates was also observed in a 2.0-L conventional stirred-tank SBR operated at biomass steady-state for Accumulibacter enrichment from activated sludge. Granules formed in this reactor showed a low abundance of Zoogloea spp. (