Using reactive tracers to detect flow field anomalies in water treatment reactors

Area of Science:

• Environmental Engineering
• Fluid Dynamics
• Chemical Engineering

Background:

• Wastewater treatment reactor hydraulics significantly influence performance and control.
• Residence time distribution offers integrated macroscopic mixing information but lacks spatial detail.
• Spatial information on macro-mixing is crucial for optimizing sensor placement and process control.

Purpose of the Study:

• To discuss the use of reactive tracers for detecting and characterizing large-scale flow structures in water and wastewater treatment reactors.
• To identify suitable reactive tracers whose reaction timescale matches the flow structure timescale.
• To demonstrate the application of this method in a real-world aeration tank.

Main Methods:

• Utilizing spatially distributed measurements of reactive tracers.
• Employing ammonium as a reactive tracer in nitrifying activated sludge systems.
• Conducting flow velocity measurements using acoustic Doppler velocimetry.
• Using ion-selective electrodes for high-temporal-resolution ammonium measurements.

Main Results:

• Reactive tracers are effective when their reaction timescale is comparable to the flow structure timescale.
• Ammonium was identified as a suitable tracer for nitrifying activated sludge systems.
• Two distinct large-scale flow features were identified in an aeration tank using distributed ammonium measurements.
• Acoustic Doppler velocimetry confirmed the identified flow field anomalies.

Conclusions:

• Spatially distributed reactive tracer measurements provide essential spatial information on macro-mixing.
• Ammonium serves as an effective reactive tracer for characterizing flow structures in aeration tanks.
• This approach enhances understanding of reactor hydraulics, aiding in process optimization and control.