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N2O Mitigation Strategies

Full-scale mitigation strategies show that sufficient and controlled aeration strategies can lower N2O emissions. However, treatment plants operated to achieve low total nitrogen effluents also have relatively low N2O emission levels.

How to Reduce N2O Emissions

Simple changes to the timing of sequential phases in an alternating activated sludge process can significantly reduce the N2O emission from the aerated phase and the accumulation in the non-aerated phase.

At Unisense Environment, we work with our clients on proving further reductions of N2O emissions. For example, through controlled influent flow balancing, recycle rates, sludge age, ammonium turnover rates, and intrinsic COD balancing.

Adjustable Process Parameters that Can Minimize the Formation and Emission of N2O:

  • Oxygen/aeration controls
  • COD/N ratio for denitrification and COD addition control
  • Turn-over rates of NH4+, NO2- and reduction of N2O accumulation
  • Load balancing influent and NH4+ from reject water
  • Phase control of nitrification and denitrification
  • Sludge age and biomass concentration
  • Recycle rates
  • Hydrolysis processes and intrinsic COD harvesting

Measure to Manage

Many researchers have demonstrated the above strategies in laboratory and pilot scale - a few have been trailed in full scale. For example, ethanol addition to SBR reactors or efficient oxygen supply. As a result, we know that N2O mitigation strategies are possible, and many at low cost, as it only involves PLC program changes. Furthermore, a steady progress in understanding the mechanisms involved in N2O emission in wastewater treatment systems will enable the development of more holistic mitigation strategies, also including other process parameters, such as the energy balance and effluent criteria.

N2O emissions from wastewater treatment processes vary substantially between plants depending on the design, operation, characteristics of wastewater, etc. However, for most of the above mitigation strategies, reliable real-time N2O monitoring is a prerequisite.