The specific sludge production (SSP) was calculated on the
basis of the balance of sludge produced and COD removed
during the 200 days of experimentation. Therefore, SSP (gTSS/
gCODremoved) was calculated dividing the amount of sludge
produced (i.e., biomass accumulation in the reactor
bed þ solids lost with the effluent þ biomass samples) by the
amount of COD removed. It should be noted, however, that
this is an overestimated value because it includes even the
start-up period of the plant characterized by low sludge ages