In fact, SVI was about 60 cm3 g1 for the bottom and medium
sludge, while itwas about 80 cm3 g1 for the sample taken from the
top of the microbial bed. Both these values indicate very good
sludge settleability; however, SVI values were lower at the bottom
as granule contribution to biomass was higher because of the
higher initial organic substrate availability.