Control of aeration, aerobic SRT and COD input for mainstream nitritation/denitritation.

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Microbial Ecology

Background:

• Conventional nitrogen removal processes often require supplemental carbon and alkalinity.
• Nitrite oxidizing bacteria (NOB) are typically more sensitive to operational changes than ammonia oxidizing bacteria (AOB).
• Optimizing nitritation/denitritation can enhance nitrogen removal efficiency in wastewater treatment.

Purpose of the Study:

• To develop and evaluate an intermittently aerated pilot-scale process for enhanced nitrogen removal.
• To optimize nitrogen removal via nitritation/denitritation without oxidized nitrogen recycle or supplemental carbon.
• To out-select nitrite oxidizing bacteria (NOB) using novel operational and process control strategies.

Main Methods:

• Operation of a 0.34 m³ pilot-scale reactor with intermittent aeration.
• Implementation of a novel aeration control strategy based on ammonia, nitrite, and nitrate set-points.
• Application of strategies including optimized chemical oxygen demand (COD) input, transient anoxia, aggressive solids retention time (SRT), and high dissolved oxygen (DO).

Main Results:

• Sustained nitrite accumulation was observed (NO2-N/NOx-N = 0.36 ± 0.27).
• Ammonia oxidizing bacteria (AOB) activity was significantly higher than NOB activity (AOB: 391 ± 124 mgN/L/d, NOB: 233 ± 151 mgN/L/d).
• Total inorganic nitrogen (TIN) removal rate of 151 ± 74 mgN/L/d was achieved at a COD/N ratio of 10.4 ± 1.9 and 25°C.

Conclusions:

• The developed online aeration control effectively out-selects NOB under mainstream conditions.
• The process achieves relatively high nitrogen removal without supplemental carbon and alkalinity.
• The pilot-scale study demonstrates the feasibility of achieving efficient nitrogen removal at a low hydraulic retention time (HRT).