A laboratory-scale granular sequencing batch
reactor, fed with acetate, was operated at two different ratios
of chemical oxygen demand to phosphorus—15:1 and 100:1.
Smaller aerobic granules, but with better settleability, were
obtained at the lower ratio. High ratio of phosphorus release
to uptake of dissolved organic carbon (0.42 mol/mol) coincided
with high percentage of polyphosphate-accumulating
organisms (up to 70 % of all bacteria) and implied high
metabolic activity of these bacteria. Polyphosphate-accumulating
organisms belonged mainly to
Accumulibacter and
Tetrasphaera
(46 and 23 %, respectively). Despite significant
abundance,
Tetrasphaera-related microorganisms
were not detected by oligoprobes Actino-221 and Actino-
658, but by broader oligoprobes Tet2-892 and Tet3-654.
Low abundance (1 %) of
Halomonas phosphatis indicated a
minor role of these bacteria in the laboratory-scale reactor
fed with synthetic wastewater. When the ratio of chemical
oxygen demand to phosphorus was increased to 100:1, deterioration
of settling properties was observed, caused by
growth of filamentous organisms from
Thiothrix
/021N
group. The higher ratio favoured
Competibacter and was
selected against all groups of polyphosphate-accumulating
organisms. However, a significant percentage (10 %) of
polyphosphate-accumulating organisms in the granular
sludge with concomitant low ratio of phosphorus release to
the uptake of dissolved organic carbon (0.01 mol/mol)
suggested shift in the overall population metabolism. Under
phosphorus limitation in wastewater, polyphosphate-accumulating
organisms no longer synthesized poly-P and behaved
as glycogen-accumulating organisms.
