Adam Muszyński, Monika Załęska-Radziwiłł
Two lab-scale sequencing batch reactors were seeded with flocculent activated sludge from a fullscale wastewater treatment plant, fed with synthetic wastewater with acetate as the only source of
organic carbon and operated in anoxic-anaerobic-aerobic (SBR1) and truly aerobic modes (SBR2). In SBR1 granules were formed, while flocs in aerobic SBR2 were overgrown with filamentous bacteria.
FISH showed that synthetic wastewater equally influenced the abundance of bacterial phyla and classes in both SBRs regardless the operating mode: Proteobacteria increased their abundance
and outcompeted Chloroflexi and Actinobacteria, Betaproteobacteria was the dominant class, abundance of Alphaproteobacteria decreased, and Gammaproteobacteria remained stable. The anoxic-
anaerobic-aerobic conditions and acetate favoured growth of polyphosphate (PAO) and glycogen accumulating organisms (GAO) in SBR1, whereas the aerobic conditions in SBR2, along with
the acetate, triggered growth of filamentous Thiothrix/021N. Despite the large differences between the abundance of PAO/GAO in both SBRs, the composition of their populations did not differ significantly
between reactors, and the type of organic substrate was a decisive factor shaping the structure of their communities. Tetrasphaera PAO, predominant in the seed, were outcompeted in
both SBRs by Accumulibacter. Clades IA and IIA, C, D together constituted 78% and 73% of the Accumulibacter lineage in SBR1 and SBR2, respectively, whereas 97% of Accumulibacter in the seed
was not targeted by any of the clade-specific probes. Defluviicoccus vanus cluster 2 was partially replaced by cluster 1 and Competibacter in both SBRs. The substantial abundance of PAO in SBR1
was reflected in the high enhanced biological phosphorus removal activity in anaerobic batch tests and high presence of intracellular polyphosphate granules at the end of the aerobic period.
Despite the significant abundance of Accumulibacter, the biomass from SBR2 neither released P nor took up Corg in anaerobic batch tests, which indicates that the activity of ecophysiological
groups was largely influenced by the mode of operating bioreactors.