Wastewater treatment facilities use enhanced biological phosphorus removal (EBPR) to meet discharge quality limits. However, the EBPR process can experience upsets due to a lack of influent carbon or inadequate anaerobic zones. By using a sidestream EBPR (S2EBPR) process, carbon can be generated internally through fermentation processes and a higher anaerobic mass fraction can be attained in smaller volumes. This study investigates nutrient removal and microbial community trends in a full-scale S2EBPR demonstration at the Calumet Water Reclamation Plant. The study aims to improve a process model of the system by better representing the activity of glycogen-accumulating organisms (GAO) and potential competitors of phosphorus-accumulating organisms (PAO), which were found in high abundance in this study. Modifying anaerobic hydrolysis, GAO glycogen storage and ORP activity parameters resulted in model prediction improvements of approximately 5% for nitrate and nitrite and 10-60% for phosphorus. The study also uses shotgun metagenomic sequencing to profile denitrification pathways of PAO and GAO. It shows that denitrifying GAO may contribute to nitric oxide reduction to a greater degree than denitrifying PAO. This study improves process modeling predictions for S2EBPR and highlights the potential role of denitrifying PAO and GAO in combined phosphorus and nitrogen removal in S2EBPR.