GRANULAZIONE AEROBICA IN UN SEQUENCING BATCH BIOFILTER REACTOR

The paper reports the results of an experimental investigation aimed at evaluating the role of shear forces on generation and properties (physical, chemical and activity) of granular biomass grown under aerobic conditions in a SBBR (i.e., Sequencing Batch Biofilter Reactor). During the start-up period, the trend of shear forces, calculated by a suitable methodology, provided a key for explaining the process of biomass granulation. In practice, at the beginning of the start up, the biofilter was characterised by rather weak shear forces values lower than 1 dyne cm-2. Under such weak forces, the biofilm increased its thickness growing with a porous structure characterized by weak adhesion strengths. Such a continuous increase of biofilm thickness produced a corresponding progressive increase of the shear forces with negative effects on biomass stability. This caused the detachment of biofilm particles that, in turn, caused a further sharp increase of the shear forces promoting the rearrangement of the detached particles in smooth granules. The granular biomass was characterised by a high density (i.e., 70-110 gVSS l-1biomass) that permitted to achieve a biomass concentration such high as 30 gVSS l-1bed without any reduction of biomass metabolic activity. Biomass density and SOURmax increased with the increase in shear force values. The extracellular polymeric substances (EPS) content of the biomass was rather low (5-6% of the total organic matter) and mostly made up of proteins. Finally, EPS content and composition were not affected by hydrodynamic shear forces.