Applying real-time control for achieving nitrogen removal via nitrite in a lab-scale CAST system

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Microbial Ecology

Background:

• Conventional nitrification-denitrification processes are energy-intensive and require significant operational control.
• Short-cut nitrification, primarily utilizing the nitrite pathway, offers potential for enhanced efficiency and reduced energy consumption in wastewater treatment.

Purpose of the Study:

• To investigate the feasibility of achieving short-cut nitrification and denitrification using a real-time control strategy in a Cyclic Activated Sludge Technology (CAST) reactor.
• To optimize nitrogen removal performance and reduce aeration energy requirements.

Main Methods:

• Operation of a 72 L bench-scale CAST reactor fed with domestic sewage.
• Implementation of an online real-time control system based on pH and oxidation-reduction potential (ORP) signals to manage anoxi-aerobic sequences.
• Gradual reduction of energy supply to nitrite-oxidizing bacteria to promote the nitrite pathway.

Main Results:

• Stable nitrogen removal performance was achieved with the real-time control strategy.
• Short-cut nitrification was successfully implemented by controlling aeration duration, leading to the dominance of the nitrite pathway.
• Aeration duration was reduced by 28.4% due to the shift towards the nitrite pathway.

Conclusions:

• The real-time control strategy is effective for stable and efficient nitrogen removal in CAST reactors.
• Short-cut nitrification via the nitrite pathway is achievable and offers significant energy savings.
• Targeted control of microbial populations, specifically nitrite-oxidizing bacteria, is key to optimizing wastewater treatment processes.