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Nitrogen removal over nitrite by aeration control in aerobic granular sludge sequencing batch reactors
Samuel Lochmatter1, Julien Maillard2, Christof Holliger3
1Laboratory for Environmental Biotechnology, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland. samuel.lochmatter@epfl.ch.
Summary
Aeration control in sequencing batch reactors effectively promotes nitrogen removal over nitrite, requiring less chemical oxygen demand (COD). This method significantly reduces nitrite-oxidizing bacteria, enhancing overall nutrient removal efficiency.
Area of Science:
- Environmental Engineering
- Microbiology
- Wastewater Treatment
Background:
- Nitrogen removal over nitrite is advantageous due to lower chemical oxygen demand (COD) requirements.
- Aerobic granular sludge in sequencing batch reactors (SBRs) is a key technology for nutrient removal.
- Controlling nitrite-oxidizing bacteria (NOB) is crucial for achieving nitrogen removal over nitrite.
Purpose of the Study:
- To investigate aeration control strategies for achieving nitrogen removal over nitrite using aerobic granular sludge.
- To analyze the impact of aeration control on nutrient removal (COD, N, P) and nitrite-oxidizing bacteria concentration.
- To evaluate the efficiency of nitrogen removal over nitrite compared to traditional nitrogen removal over nitrate.
Main Methods:
- Utilized sequencing batch reactors (SBRs) with aerobic granular sludge.
- Implemented aeration phase length control combined with intermittent or alternate high-low dissolved oxygen (DO) strategies.
- Monitored nutrient removal efficiencies (COD, N, P) and quantified nitrite-oxidizing bacteria populations.
- Conducted experiments at different temperatures (20 °C and 15 °C).
Main Results:
- Aeration control successfully reduced nitrite-oxidizing bacteria populations by over 95% at 20 °C within 60 days.
- Achieved up to 95% nitrogen removal efficiency with a COD:N:P ratio of 20:2.5:1, at a rate of 0.18 kgN·m-3·d-1.
- Nitrogen removal efficiency was only 74% when relying on nitrogen removal over nitrate.
- The aeration control strategy maintained the nitrite pathway even at 15 °C, despite higher nitrite-oxidizing bacteria growth rates.
Conclusions:
- Aeration control, specifically phase length and high-low DO strategies, is an effective method for achieving nitrogen removal over nitrite with aerobic granular sludge.
- This approach significantly reduces nitrite-oxidizing bacteria, enabling efficient nutrient removal, especially when COD is limited.
- The system demonstrated flexibility, allowing for switching between nitrogen removal pathways and maintaining the nitrite pathway at lower temperatures.
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