Unwanted mainstream nitritation-denitritation causing massive N2O emissions in a continuous activated sludge process.
A Kuokkanen1, K Blomberg1, A Mikola2
1Helsinki Region Environmental Services Authority Helsinki and Aalto University: Espoo, Wastewater Treatment, P.O. Box 320, FI-00066 HSY, Finland
Summary
High nitrite accumulation in wastewater treatment can unexpectedly increase nitrous oxide (N2O) emissions, a potent greenhouse gas. This study highlights the risk of significant N2O release from activated sludge processes due to process disturbances.
Area of Science:
- Environmental Science
- Environmental Engineering
- Water Treatment
Background:
- Nitrous oxide (N2O) is a significant greenhouse gas contributing to the carbon footprint of wastewater treatment.
- Conventional nitrogen removal processes are generally assumed to have moderate N2O emissions.
- Process disturbances and nitrite accumulation can elevate N2O emission risks.
Purpose of the Study:
- To investigate spontaneous, high nitrite accumulation in a municipal wastewater treatment plant's activated sludge process.
- To quantify the resulting nitrous oxide emissions.
- To assess the implications for greenhouse gas emissions from wastewater treatment.
Main Methods:
- Observation of elevated nitrite levels in activated sludge effluent across multiple treatment lines.
- Monitoring of nitrous oxide emissions linked to nitrite accumulation.
- Analysis of nitrogen load and N2O emission data.
Main Results:
- Spontaneous and sustained high nitrite (NO2-) levels were observed in the activated sludge effluent.
- These high nitrite levels correlated with dramatically increased nitrous oxide (N2O) emissions.
- Up to 20% of the daily influent nitrogen load was emitted as N2O.
Conclusions:
- High nitrite accumulation can occur in conventional activated sludge processes, leading to substantial N2O emissions.
- This highlights potential risks for increased greenhouse gas emissions, particularly concerning nitritation-denitritation processes.
- Continuous monitoring and control of N2O emissions are crucial for effective wastewater treatment management.
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