This paper reports the results of an experimental study specifically aimed at developing a simple methodology for calculating hydrodynamic shear forces in a sequencing batch biofilm reactor (SBBR) system with granular biomass. Using such a methodology, the hydrodynamic shear forces are simply calculated by measuring bed porosity and pressure losses. In addition, by applying this methodology an explanation for the biomass evolution from biofilm to granules under aerobic conditions has been provided and the following mechanism has been proposed: (i) formation of a thin biofilm that fully covers the carrier; (ii) increase of biofilm thickness; (iii) break-up of the attached biofilm with release of biofilm particles; (iv) rearrangement of biofilm particles in smooth granules. The hydrodynamic shear forces trend during the start-up period provides an explanatory key for the generation process of granular biomass. In fact, during the first two steps, the SBBR is characterized by rather weak shear forces values (lower than 1 dyn/cm2). Under these weak shear forces, the biofilm grows by increasing its thickness through a porous structure and weak adhesion strengths. Such a continuous increase of biofilm thickness produces an increase of the shear forces with negative effect on biomass stability, causing the detachment of biofilm particles. In turn, such detachment causes a further sharp increase of shear forces (more than 10 times) that promotes the rearrangement of the detached biofilm particles in smooth granules. A correlation between biomass density and hydrodynamic shear forces was observed. In particular, the biomass density linearly increases with the increase of shear stress.

The paper reports the results of a laboratory investigation aimed at evaluating the effectiveness of an innovative technology, SBBGR (sequencing batch biofilter granular reactor), based on aerobic granular biomass, for treating diluted (i.e., municipal wastewater) or concentrated (i.e., municipal landfill leachates) wastewater. When this technology was applied to the treatment of municipal wastewater, the results showed that, even at maximum organic load (i.e., 7 (kg of COD)/m3·d), the chemical oxygen demand (COD) in the treated effluent was lower than 50 mg/L. In addition, total Kjeldahl nitrogen (TKN) removal efficiency was higher than 87% up to an organic load of 5.7 (kg of COD)/m3·d, corresponding to a nitrogen load of 0.8 (kg of TKN)/m3·d. During the treatment of a mature municipal landfill leachate, the SBBGR proved suitable for removing the entire biodegradable compound content (i.e., about 80% of the COD content of the leachate) up to an applied organic loading value of 1.1 (kg of COD)/m3·d. During the whole investigation, the process was characterized by a low sludge production, about 1 order of magnitude lower than that of conventional systems.

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This paper reports the results of the treatment of a yarn dyeing effluent using an integrated biologicalchemical oxidation process. In particular, the biological unit was based on a sequencing batch biofilter granular sludge reactor (SBBGR), while the chemical treatment consisted of an ozonation step. Biological treatment alone was first performed as a reference for comparison. While biological treatment did not produce an effluent for direct discharge, the integrated process assured good treatment results, with satisfactory removal of chemical oxygen demand (up to 89.8 %), total nitrogen (up to 88.2 %), surfactants (up to 90.7 %) and colour (up to 99 %), with an ozone dose of 110 mg of ozone per litre of wastewater. Biomass characterization by fluorescence in situ hybridization has revealed that filamentous bacteria represented about 20 % of biomass (coherently with high sludge volume index values); thanks to its special design, SBBGR guaranteed, however, stable treatment performances and low effluent suspended solids concentrations, while conventional activated sludge systems suffer from sludge bulking and even treatment failure in such a condition. Furthermore, biomass characterization has evidenced the presence of a shortcut nitrification-denitrification process.