Low temperature MBBR nitrification: Microbiome analysis.

Area of Science:

• Environmental microbiology
• Wastewater treatment engineering
• Bioreactor technology

Background:

• Moving bed biofilm reactors (MBBRs) are crucial for nitrification in post-carbon removal processes.
• Temperature significantly impacts biological treatment efficiency, particularly nitrification rates.

Purpose of the Study:

• To investigate nitrification performance in MBBRs during the transition from 20°C to 1°C and during sustained low-temperature operation.
• To elucidate temperature effects on ammonia removal rates, microbial community structure, and cell viability.

Main Methods:

• Four pilot-scale nitrifying MBBR reactors were operated at varying ammonia loading rates.
• Arrhenius temperature correction coefficients were used to model nitrification rates.
• Microbial community analysis and cell viability assessments were performed.

Main Results:

• Steady-state ammonia removal rates at 1°C were 22.8% of those at 20°C, with an Arrhenius correction factor of 1.086.
• Microbial diversity decreased at 1°C, though approximately 2000 bacterial species were identified.
• Nitrosomonads (AOB) and Nitrospira (NOB) remained dominant across temperatures.
• Increased viable biomass and thicker biofilms at 1°C partially compensated for reduced per-cell activity.
• High ammonia loading at 1°C reduced removal rates and enriched stress response pathways.

Conclusions:

• Nitrification in MBBRs is significantly reduced at 1°C, but enhanced biomass can partially mitigate performance loss.
• Bacterial community structure adapts to low temperatures, maintaining dominant ammonia and nitrite oxidizers.
• Optimal loading conditions are crucial for maintaining nitrification efficiency at low temperatures.