Optimization Strategies: BOD to P (Des Moines Case Study)

The Des Moines WRA’s nitrification activated sludge process has been previously optimized for energy efficiency by reducing airflow with staggered dissolved oxygen (DO) concentrations in passes one through four of their six-basin process. A second optimization step to provide enhanced biological phosphorus removal (EBPR) has been tested by decreasing and cycling air flow in the first pass to achieve anoxic/anaerobic conditions with DO concentrations measuring less than 0.1 mg/L and average oxidation reduction potential (ORP) concentration of about -130 mV. EBPR activity was successfully established in the modified basins with average phosphorus mass content of the waste sludge 3.2 ± 0.2% (95% confidence) compared to 1.6 ± 0.1% in the control basin. A wet weather scenario was also tested by operating in contact stabilization mode in order to protect the first pass from high DO entrained influent waste streams. Results showed effluent phosphorus concentrations less than 1 mg-P/L could be achieved and operation in contact stabilization mode provided some protection to the first pass.