Dynamics of Microbial Community Structure of and Enhanced Biological Phosphorus Removal by Aerobic Granules Cultivated on Propionate or Acetate

ABSTRACTAerobic granules are dense microbial aggregates with the potential to replace floccular sludge for the treatment of wastewaters. In bubble-column sequencing batch reactors, distinct microbial populations dominated propionate- and acetate-cultivated aerobic granules after 50 days of reactor operation when only carbon removal was detected. Propionate granules were dominated byZoogloea(40%),Acidovorax, andThiothrix, whereas acetate granules were mainly dominated byThiothrix(60%). Thereafter, an exponential increase in enhanced biological phosphorus removal (EBPR) activity was observed in the propionate granules, but a linear and erratic increase was detected in the acetate ones. BesidesAccumulibacterandCompetibacter, other bacterial populations found in both granules were associated withChloroflexusandAcidovorax. The EBPR activity in the propionate granules was high and stable, whereas EBPR in the acetate granules was erratic throughout the study and suffered from a deterioration period that could be readily reversed by inducing hydrolysis of polyphosphate in presumably saturatedAccumulibactercells. Using a newppk1gene-based dual terminal-restriction fragment length polymorphism (T-RFLP) approach revealed thatAccumulibacterdiversity was highest in the floccular sludge inoculum but that when granules were formed, propionate readily favored the dominance ofAccumulibactertype IIA. In contrast, acetate granules exhibited transient shifts between type I and type II before the granules were dominated byAccumulibactertype IIA. However,ppk1gene sequences from acetate granules clustered separately from those of propionate granules. Our data indicate that the mere presence ofAccumulibacteris not enough to have consistently high EBPR but that the type ofAccumulibacterdetermines the robustness of the phosphate removal process.