Performance and microbial adaptation of a continuous granular sludge-type nitritation process facing the decreasing...

Area of Science:

• Environmental Science
• Microbiology
• Wastewater Treatment Engineering

Background:

• Nitritation is crucial for energy-efficient nitrogen removal via anammox processes.
• Low temperatures typically cause operational instability in nitritation.
• Conventional treatment requires energy-intensive heating in cold climates.

Purpose of the Study:

• To investigate the feasibility of nitritation at an ultralow temperature of 5.0 ℃.
• To assess the performance and stability of a continuous-flow aerobic granular sludge (CAGS) reactor under cold conditions.
• To understand the microbial and sludge characteristics influencing nitritation at low temperatures.

Main Methods:

• Operation of a CAGS reactor with a fixed ammonium load (250.0 mg/L) and hydraulic retention time (12.0 h).
• Stepwise temperature reduction from 25.0 ℃ to 5.0 ℃.
• Analysis of microbial community (AOB, nitrite-oxidizing bacteria, denitrifying bacteria), sludge properties (size, calcium content), and gene abundance (amo genes).

Main Results:

• Stable nitritation achieved at 5.0 ℃ with a nitrite production rate of 0.29 kg/m³d and efficiency of 59.77%.
• Ammonium-oxidizing bacteria (AOB) activity was partially inhibited; Nitrosomonas was the sole AOB genus.
• Sludge granules reduced in size and calcium content but maintained function; nitrite-oxidizing bacteria were suppressed.
• Relative abundance of amo genes remained stable, ensuring nitritation stability.

Conclusions:

• Nitritation is feasible and stable at ultralow temperatures (5.0 ℃) using CAGS reactors.
• Sludge characteristics and microbial community shifts contribute to stable performance in cold conditions.
• Findings redefine nitritation operational boundaries, enabling cost-effective nitrogen removal in cold climates without heating.