Synergistic operational optimizations and microbial responses stabilize filamentous-dominated continuous-flow partial...

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biogeochemical Cycles

Background:

• Continuous-flow partial denitrification-anammox (PD/A) systems face challenges with operational stability due to low nitrite supply and temperature sensitivity of anammox bacteria.
• Excessive filamentous bacteria growth often compromises reactor performance and stability, especially under cold conditions.

Purpose of the Study:

• To demonstrate stable nitrogen removal in a filamentous-dominated PD/A reactor under low-temperature stress.
• To investigate the microbial community structure, genomic potential, and adaptive strategies enabling stable operation.

Main Methods:

• Utilized a continuous-flow PD/A reactor operated at an average temperature of 16.7°C.
• Employed operational optimizations and engineered biomass retention (mesh filtration, sludge return).
• Conducted metagenomic analysis and genome-centric reconstruction to characterize microbial communities and their functional capabilities.

Main Results:

• Achieved 89.8% total nitrogen removal, with high efficiencies for ammonium (97.2%) and nitrate (91.5%).
• The filamentous genus Sphaerotilus dominated but possessed genomic potential for nitrite provision.
• Synergistic interactions between Sphaerotilus, other heterotrophs, and enhanced biomass retention supported Ca. Brocadia enrichment and low-temperature adaptation.

Conclusions:

• Strategic biomass retention combined with microbial adaptive responses can ensure stable nitrogen removal in filamentous-dominated PD/A systems.
• Sphaerotilus and other heterotrophs play a crucial role in supporting anammox bacteria by ensuring nitrite availability.
• Ca. Brocadia demonstrated enhanced low-temperature adaptability through metabolic pathway expansion and increased cold shock protein expression.