The optimal dissolved oxygen profile in a nitrifying activated sludge process - comparisons with ammonium feedback...

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Process Control

Background:

• Ammonium feedback control is crucial for optimizing dissolved oxygen (DO) set-points in activated sludge processes for nitrogen removal.
• Wastewater treatment plants seek efficient methods to reduce energy consumption, particularly air flow rates.

Purpose of the Study:

• To compare the performance of proportional-integral (PI) ammonium feedback control with a DO profile optimized for minimal air flow.
• To evaluate energy savings achievable through different control strategies under varying plant loads and DO concentrations.

Main Methods:

• Simulated scenarios using a three-aerated-zone model with daily variations in influent ammonium concentration.
• Comparison of PI ammonium control (with limited integral action and maximum DO set-point) against constant DO control and an optimal air flow minimization strategy.
• Investigation of ammonium sensor placement effects.

Main Results:

• The best-performing ammonium PI controller achieved 1-3.5% savings in air flow rate compared to constant DO control.
• An optimal air flow minimization strategy yielded 3-7% savings.
• Energy savings were more significant at higher dissolved oxygen concentrations.

Conclusions:

• Ammonium feedback control, when optimized, can lead to substantial energy savings in nitrogen removal processes.
• Limiting the DO set-point and minimizing integral action in PI controllers enhances performance.
• The findings support the implementation of advanced control strategies for more efficient wastewater treatment.