Stability of partial nitrification and microbial population dynamics in a bioaugmented membrane bioreactor

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Bioreactor Technology

Background:

• Partial nitrification processes often neglect stable nitrite accumulation, hindering efficient nitrogen removal.
• Bioaugmentation using enriched ammonia-oxidizing bacteria (AOB) offers a potential solution for improving bioreactor performance.
• Understanding the impact of operational parameters on microbial communities is crucial for process stability.

Purpose of the Study:

• To develop a bioaugmented membrane bioreactor (MBM) for stable nitrite accumulation.
• To evaluate the effects of dissolved oxygen (DO) and temperature on partial nitrification stability and microbial community structure.
• To identify optimal conditions for maximizing nitrite accumulation in the MBR.

Main Methods:

• Development of a bioaugmented membrane bioreactor (MBR).
• Inoculation with enriched ammonia-oxidizing bacteria (AOB).
• Analysis of microbial community structure using Denaturing Gradient Gel Electrophoresis (DGGE) and Fluorescence In Situ Hybridization (FISH).

Main Results:

• Optimal conditions for stable partial nitrification were 2-3 mg DO/L and 30°C, achieving 95% ammonia oxidation and a 0.95 nitrite ratio.
• High DO (5-6 mg/L) and low temperature (20°C) negatively impacted nitrite accumulation, reducing the ratio to 0.6.
• Nitrosomonas-like AOB predominated, coexisting with heterotrophic bacteria, and a high AOB to nitrite-oxidizing bacteria (NOB) ratio (54-77% vs. 0.4-0.9%) contributed to stable nitrite accumulation.

Conclusions:

• Dissolved oxygen and temperature are critical factors for maintaining stable partial nitrification in bioaugmented MBRs.
• The bioaugmented MBR achieved high and stable nitrite accumulation, outperforming many previous studies.
• The predominance of specific AOB and a high AOB/NOB ratio are key to successful nitrite accumulation in this system.