Nitrification in sequencing biofilm batch reactors: lessons from molecular approaches

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Wastewater Treatment

Background:

• Sequencing biofilm batch reactors (SBBRs) treat sewage with high ammonia and salt concentrations.
• Nitrifying microbial communities are essential for nutrient removal in wastewater treatment plants (WWTPs).

Purpose of the Study:

• To analyze the diversity and population structure of nitrifying microbes in an SBBR under high ammonia and salt conditions.
• To investigate ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) diversity and abundance.
• To explore the morphology and metabolic capabilities of uncultured Nitrospira-like bacteria.

Main Methods:

• Full-cycle rRNA approach for microbial diversity analysis.
• Ammonia monooxygenase (amoA) gene fragment sequencing for ammonia-oxidizer investigation.
• Fluorescent In situ Hybridization (FISH) and digital image analysis for quantification.
• Competitive PCR for amoA gene quantification.
• Confocal laser scanning microscopy (CLSM) and microautoradiography for morphology and substrate uptake studies.

Main Results:

• High diversity of ammonia- and nitrite-oxidizers was found in the SBBR despite extreme conditions.
• Novel ammonia-oxidizers were identified.
• Ammonia-oxidizers were more abundant and occupied a larger biovolume than nitrite-oxidizing bacteria.
• A complex microchannel network was observed in Nitrospira-like bacteria microcolonies.
• Nitrospira-like bacteria demonstrated CO2 utilization and organic substrate uptake.

Conclusions:

• Wastewater treatment plants with high ammonia and salt loads can harbor diverse nitrifying communities.
• Understanding nitrifier microbial ecology is key to improving nutrient removal efficiency in WWTPs.
• Novel microbial insights contribute to the fundamental knowledge of nitrifier behavior in engineered ecosystems.