Reducing nitrous oxide emission in a sequencing batch reactor operated as static/aerobic/anoxic (SOA) process

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Greenhouse Gas Mitigation

Background:

• The conventional anaerobic/anoxic/oxic (A2/O) process is widely used for biological nutrient removal (BNR).
• Nitrous oxide (N2O) emissions from wastewater treatment pose environmental concerns.
• The static/aerobic/anoxic (SOA) activated sludge process is an alternative for BNR.

Purpose of the Study:

• To investigate and compare N2O emission characteristics of the SOA process versus the conventional A2/O process.
• To optimize the SOA process for enhanced N2O mitigation and biological nutrient removal.
• To understand the impact of static phase duration on N2O generation and nutrient removal efficiency.

Main Methods:

• Implementation of the SOA activated sludge process with varying static phase durations (60 min, 30 min, 15 min).
• Comparison of N2O emission factors and biological nutrient removal (BNR) performance against a control A2/O process.
• Analysis of carbon source consumption during the aerobic phase to correlate with N2O production.

Main Results:

• The SOA process, while effective for BNR, initially showed increased N2O emissions compared to A2/O.
• Shortening the static time in the SOA process significantly reduced N2O emissions.
• SOA with a 30-minute static time demonstrated optimal N2O mitigation (emission factor reduced from 7.32% to 3.69% of total nitrogen removed) and superior phosphorus removal compared to 15-minute static time.
• Reduced N2O generation in the 30-minute static SOA process was linked to increased consumption of external carbon sources at the aerobic phase's onset.

Conclusions:

• The modified SOA process, particularly with a 30-minute static phase, offers a promising alternative for simultaneous biological nutrient removal and N2O mitigation.
• Optimizing static phase duration is crucial for balancing BNR efficiency and minimizing greenhouse gas emissions in SOA systems.
• Further research into carbon source dynamics can refine SOA process design for enhanced environmental performance.