Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures

Area of Science:

• Environmental Microbiology
• Wastewater Engineering
• Biotechnology

Background:

• Mainstream anammox processes offer potential for energy autarky in wastewater treatment plants.
• Assessing the stability and reliability of partial nitritation/anammox (PN/A) at low temperatures is crucial for practical application.

Purpose of the Study:

• To evaluate the long-term stability of PN/A processes at low temperatures (down to 15°C).
• To determine the reliability of PN/A systems in meeting stringent nitrogen discharge limits (<2 mg NH4+-N·L⁻¹ and <10 mg Ntot·L⁻¹).

Main Methods:

• Operation of two parallel 12-L sequencing batch reactors (MBBR and H-MBBR) for over a year.
• Utilizing aerobically pre-treated municipal wastewater with controlled low oxygen concentrations.
• Monitoring nitrogen removal, organic micropollutant removal, and microbial community composition (16S rRNA gene sequencing).

Main Results:

• Stable PN/A operation achieved at 15°C with low nitrate production (16% in MBBR).
• High nitrogen removal rates (20-40 mgN·L⁻¹·d⁻¹) and efficiencies (>90% ammonium, >70% total nitrogen) were maintained.
• Effluent total nitrogen consistently below 10 mgN·L⁻¹, reaching 6 mgN·L⁻¹ in MBBR.
• Comparable removal of organic micropollutants to conventional treatments.
• Temporary suppression of anammox activity at 11°C, with rapid recovery upon re-warming.

Conclusions:

• PN/A systems demonstrate long-term stability and reliability for nitrogen removal from municipal wastewater, even under low-temperature conditions.
• These systems can effectively meet strict discharge limits and compete with conventional biological nutrient removal processes.
• The bacterial community was dominated by "Candidatus Brocadia", indicating suitability for mainstream PN/A applications.