Controlling the COD removal of an A-stage pilot study with instrumentation and automatic process control

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Biotechnology

Background:

• The A/B process is crucial for autotrophic nitrogen removal via anaerobic ammonium oxidation (anammox).
• High-rate operation of the A-stage leads to variable chemical oxygen demand (COD) removal, affecting downstream nitrogen removal.
• Lack of automatic process control exacerbates COD removal variability in the A-stage.

Purpose of the Study:

• To evaluate dissolved oxygen (DO) and mixed liquor suspended solids (MLSS) based automatic control strategies in the A-stage of an A/B pilot study.
• To reduce COD removal variability in the A-stage and consequently, the effluent C/N variability.
• To assess the impact of these control strategies on nitrogen removal efficiency.

Main Methods:

• Implementation of in situ on-line sensors for real-time monitoring of DO and MLSS.
• Application of cascade DO control strategy in the A-stage.
• Utilization of MLSS-based solids retention time (SRT) control as a surrogate for SRT management.
• Pilot-scale A/B system operation under controlled conditions.

Main Results:

• Cascade DO control did not significantly impact COD removal when DO levels were maintained above 0.5 mg/L.
• MLSS-based SRT control reduced COD removal variation in the A-stage by 90%.
• Effluent C/N variability was not significantly reduced by the MLSS-based control strategy under the tested conditions.

Conclusions:

• MLSS-based control is effective in stabilizing COD removal in the A-stage of A/B processes.
• Further optimization may be needed to address effluent C/N variability.
• Automatic control strategies show promise for enhancing the performance of autotrophic nitrogen removal systems.