Performance and microbial community composition dynamics of aerobic granular sludge from sequencing batch bubble column reactors operated at 20 A°C, 30 A°C, and 35 A°C

Two bubble column sequencing batch reactors fed with an artificial wastewater were operated at 20 A degrees C, 30 A degrees C, and 35 A degrees C. In a first stage, stable granules were obtained at 20 A degrees C, whereas fluffy structures were observed at 30 A degrees C. Molecular analysis revealed high abundance of the operational taxonomic unit 208 (OTU 208) affiliating with filamentous bacteria Leptothrix spp. at 30 A degrees C, an OTU much less abundant at 20 A degrees C. The granular sludge obtained at 20 A degrees C was used for the second stage during which one reactor was maintained at 20 A degrees C and the second operated at 30 A degrees C and 35 A degrees C after prior gradual increase of temperature. Aerobic granular sludge with similar physical properties developed in both reactors but it had different nutrient elimination performances and microbial communities. At 20 A degrees C, acetate was consumed during anaerobic feeding, and biological phosphorous removal was observed when Rhodocyclaceae-affiliating OTU 214 was present. At 30 A degrees C and 35 A degrees C, acetate was mainly consumed during aeration and phosphorous removal was insignificant. OTU 214 was almost absent but the Gammaproteobacteria-affiliating OTU 239 was more abundant than at 20 A degrees C. Aerobic granular sludge at all temperatures contained abundantly the OTUs 224 and 289 affiliating with Sphingomonadaceae indicating that this bacterial family played an important role in maintaining stable granular structures.