Biogranulation and Physical Properties of Aerobic Granules in Reactors at Low Organic Loading Rate and with Powdered Ceramsite Added

In wastewater treatment, aerobic granular sludge (AGS) technology is a relatively new alternative to the activated sludge method. The biogranulation of biomass ensues when appropriate environmental conditions in a reactor are ensured, and one of the factors determining this is the organic loading rate (OLR). As a literature review suggests, the optimal values of OLR for AGS technology are in the range of 2.50–7.50 g COD/(dm3∙d), the aim of the work detailed here was to evaluate the impact of powdered ceramsite on biogranulation in two Granular Sequencing Batch Reactors (GSBRs) in which OLR was equal to just 2.10 g COD/(dm3∙d) (R1) and 1.0 g COD/(dm3∙d) (R2). The research was carried out in laboratory scale with using synthetic wastewater containing different concentration of organic compounds. In the course of the research, a more intensive process of biogranulation was noted in reactor R1, and mean diameters of granules on the last day of experimentation were 962 and 274 µm for R1 and R2, respectively. While the organic loading rate equal to 2.10 g COD/(dm3∙d) could allow granule formation, the results also pointed that lower food-to-microorganism (F/M) ratios favour biogranulation. This parameter was indirectly affected by the application of powdered ceramsite, because the powdered material improved the sludge sedimentation properties (average values of SVI30 being 30.1±12.8 and 36.9±10.9 cm3/g). The result of this was more-limited leaching of biomass from reactors (with average values for MLVSS at 4.37±1.23 and 3.03±0.67 g/dm3)