Professor, Department of Civil Engineering, University of Calgary, Canada

Speech Title: Simultaneous COD and nutrients removal by aerobic granular sludge and the influence of C/N/P ratio

Abstract: Aerobic granulation is a very promising technology as it can achieve simultaneous chemical oxygen demand (COD) and nutrients (nitrogen and phosphate) removal in one sequencing batch reactor. However, the mechanisms of nitrogen and phosphate removal in aerobic granular sludge reactor can be different from conventional activated sludge process. In this study, various organic loading rates (OLR) were tested as well as various nutrient levels from nutrient rich conditions to severe nitrogen deficient conditions. Four pilot scale (20 L) reactors were operated, with OLR ranging from 2-30 kg COD/m³•day and C/N/P ratio ranging from 100/50/10 to 100/1.2/0.1, with C given in terms of COD. Satisfactory removal of COD, nitrogen and phosphate can be achieved under all tested conditions, except when influent ammonium concentration reached a certain threshold. The results indicate that relatively higher OLR can accelerate aerobic granule formation, while an OLR that is too high leads to granule disintegration under nutrient deficient conditions. Microbial community analysis showed that with high COD to nutrient ratio under aerobic conditions, heterotrophic bacteria could easily outcompete slow growing bacteria such as ammonia oxidizing bacteria (AOB) and phosphate-accumulating organisms (PAO). Satisfactory nutrient removal can potentially be achieved by heterotrophic nitrification or simply by assimilation and precipitation. Lower C/N ratio combined with some operational factors can likely help with the enrichment of slow growing bacteria such as AOB after a while. Phosphorus releasing was not detected during the run which may indicate that phosphate removal in aerobic granular reactor may not follow the conventional pathway. Some PAO exist in the microbial community, but there can likely be other organisms that contribute to phosphate removal in aerobic granular reactors. However, high phosphate level and further tests will be needed to confirm this.