The change in biomass structure from the activated sludge
used as inoculum to SBBGR biomass caused a reduction of the
active bacterial fraction from 85% to about 45%. Such a
reduction is a consequence of both the high sludge age and the
low specific biomass organic load (kgCOD/kgVSS d) in the labscale
SBBGR compared with activated sludge systems.