A control strategy for reducing aeration costs during low loading periods

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Process Optimization

Background:

• Activated sludge processes rely on efficient aeration systems for effective wastewater treatment.
• Aeration systems in full-scale basins often require optimization, especially during varying load conditions like summer low loading periods.
• Dissolved oxygen (DO) concentration is a key parameter for controlling aeration efficiency.

Purpose of the Study:

• To improve the efficiency of an aeration system in a full-scale activated sludge basin during low loading periods.
• To evaluate the impact of different dissolved oxygen (DO) setpoint combinations on oxygen transfer efficiency and air flow rates.
• To identify cost-saving strategies for aeration system operation.

Main Methods:

• Dynamic off-gas testing was employed to measure standardized oxygen transfer efficiency (alphaSOTE).
• Four different DO setpoint combinations were tested over one-week periods in a three-zone activated sludge basin.
• The study analyzed the relationship between alphaSOTE and specific diffuser flow rate (qD) for each aeration zone.

Main Results:

• Lowering DO setpoints initially decreased the total air flow rate to the basin.
• A low DO in the initial zones shifted the treatment load towards the latter zones.
• The relationship between alphaSOTE and qD varied significantly across the three zones, with Zone 1 showing a strong decrease as qD increased.

Conclusions:

• Adjusting DO setpoints is an effective strategy for optimizing aeration efficiency and reducing energy consumption in activated sludge systems.
• Aeration costs were reduced by 15% with the most efficient DO setpoint combination tested.
• A control strategy adjusting oxygen transfer rates based on DO setpoints is proposed for further cost savings while meeting effluent requirements.