Bioaugmentation with Nitrifying Granules in Low-SRT Flocculent Activated Sludge at Low Temperature

Area of Science:

• Environmental Microbiology
• Wastewater Engineering
• Biotechnology

Background:

• Low temperatures and short solids retention times (SRT) challenge nitrification in activated sludge systems.
• Municipal anaerobic digestion centrate is a potential nutrient source for nitrifying organisms.

Purpose of the Study:

• To investigate the effectiveness of bioaugmentation using nitrifying granules to enhance nitrification capacity in a low-temperature activated sludge system.
• To assess the stability and microbial community dynamics of nitrifying granules under mainstream conditions.

Main Methods:

• Nitrifying granules were cultivated in a sidestream reactor using municipal anaerobic digestion centrate.
• Granules were introduced via bioaugmentation into a non-nitrifying mainstream activated sludge system operating at 12 °C and a 2.5-day SRT.
• Effluent quality, microbial community structure, and nitrification activity were monitored.

Main Results:

• Bioaugmentation achieved effluent NH3-N concentrations below 1 mg/L.
• Nitrification capacity was maintained even after initial granule activity decreased, attributed to new granule growth.
• Molecular analyses confirmed nitrifying bacteria remained attached to granules with minimal washout.

Conclusions:

• Bioaugmentation with nitrifying granules is a viable strategy to intensify nitrification in challenging low-temperature, low-SRT activated sludge systems.
• This approach effectively achieves low effluent ammonia concentrations and contributes to overall nitrogen removal.
• The study highlights the resilience and growth potential of nitrifying granules in mainstream wastewater treatment.