Aerobic granular sludge sbr limits and performances

Aerobic granular sludge has several advantages over conventional activated sludge flocs such as fast settling ability, high biomass retention and ability to withstand high organic loading including potential toxic substrates, leading towards a compact reactor system – aerobic granular sludge sequential batch reactor (AGSBR). After successfully cultivating aerobic granules in SBR systems from flocculated activated sludge fed with synthetic medium with acetate as the sole carbon source or with real municipal wastewater, we investigated the possibility of AGSBR to simultaneously remove the organic loading, nitrogen and phosphorus content. The experiments were performed in a SBR reactor, at loadings rates of up to 3.0 kg m-3 day-1 COD and 0,2 kg m-3day-1 of N-NH4+. Compact granules with good settling ability were maintained during the experimental period and high (>95%) COD removal but insufficient global nitrogen (65%) and phosphorus (62%) removal efficiencies were registered.
The size of the granule is closely related to the size of the anoxic zone: the lower the oxygen concentration or the bigger the granule, the larger the anoxic zone and thus, the larger the nitrogen and phosphorus removal capacity. In our study, the aeration intensity was maintained constant during the entire reaction period, in order to maintain the hydrodynamic shear forces within the reactor and implicitly the compact structure of the granules. The processes of COD removal, nitrification, denitrification and phosphorus removal can occur simultaneously in an aerobic granular sludge reactor fed with acetate. However, in case of higher concentrations of influent nitrogen and phosphorus different aeration or feeding strategies should be considered.