Explain enhanced biological phosphorus removal (EBPR) in wastewater treatment.

Enhanced biological phosphorus removal utilizes polyphosphate-accumulating organisms (PAOs), particularly Candidatus Accumulibacter, to remove phosphorus beyond normal assimilation. Mechanism: In anaerobic zone (no oxygen or nitrate), PAOs release stored polyphosphate to gain energy for uptake of volatile fatty acids (VFAs), storing them as polyhydroxyalkanoates (PHA). In aerobic zone, PAOs oxidize PHA for energy, taking up phosphorus in excess of normal needs (luxury uptake) and storing it as polyphosphate. Process configurations: A2O (anaerobic-anoxic-aerobic), UCT (University of Cape Town), and Bardenpho systems integrate P and N removal. Requirements: sufficient VFAs (fermentable BOD), true anaerobic conditions (nitrate recycle minimized), adequate aerobic zone for P uptake. Challenges: competition from glycogen-accumulating organisms (GAOs) under high temperature or low pH; nitrate intrusion to anaerobic zone. Sludge contains 5-7% P versus 1-2% normally, requiring proper disposal/recovery.