Development of aerobic granular sludge in sequencing batch reactors with low sedimentation speed

Abstract

Several studies have shown the formation of aerobic granular sludge in reactors where high sedimentation rates are imposed, varying from 10 to 12 m.h-1. Apparently, when the settling velocity is less than 3.8 m.h-1, the fraction of flocculated sludge is predominant, since the suspended sludge is not effectively eliminated from the reactor. Other studies, however, show the formation of aerobic granular sludge at velocities lower than this, pointing to the possibility of formation of this type of biomass at even lower speeds. Thus, this work evaluated the efficacy of this type of sludge in reactors treating sewage, with H/D ratio (height/diameter), for sedimentation velocities of 1.8 and 1.2 mh-1, verifying the efficiencies of organic matter and nitrogen. The results indicated that it is possible to form aerobic granular sludge for the study velocity range, but with low structural stability from diameters of approximately 1.2 mm. This instability of the granules contributes to the low efficiency of removal of organic matter and nitrogen in the reactors.