Floc-based sequential partial nitritation and anammox at full scale with contrasting N2O emissions

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Nitrogen Removal Processes

Background:

• New Activated Sludge (NAS®) is a hybrid, floc-based nitrogen removal process.
• It operates without external carbon addition, relying on controlled sludge retention times (SRT) and dissolved oxygen (DO) levels.

Purpose of the Study:

• To evaluate the performance of a retrofitted four-stage NAS® plant.
• To conduct on-line measurements of greenhouse gas emissions (N2O and CH4) during treatment.

Main Methods:

• The study treated anaerobically digested industrial wastewater with high nitrogen and COD content.
• A batch-fed partial nitritation step controlled SRT and DO to oxidize nitrogen.
• Subsequent anammox, denitrification, and nitrification compartments followed, with an overall SRT of 46 days.

Main Results:

• The partial nitritation step achieved 45-47% nitrite and 13-15% nitrate oxidation, with 5.1-6.6% N2O emission at SRT 1.7 d and DO 1.0 mg O2/L.
• The anammox step removed 0.26 kg N m⁻³ d⁻¹, with Kuenenia genus contributing 71%.
• Overall nitrogen removal efficiency reached 95%, producing a dischargeable effluent. Greenhouse gas emissions (N2O and CH4) were monitored.

Conclusions:

• Retrofitted NAS® significantly reduced operational costs by 40% compared to traditional methods.
• While effective for nitrogen removal, a 50% reduction in N2O emissions is required for a CO2-neutral footprint.
• Methane (CH4) emissions had a considerably lower impact.