Effect of organics on nitrous oxide emission during wastewater nitrification with enriched nitrifiers

• The effect of organics on N2O emission during nitrification was investigated.
• Wastewater with organics yielded more N2O than wastewater without organics.
• The COD/N ratio significantly influenced N2O emission during nitrification.
• Higher NH4+NH4+ and nitrite concentrations and aeration rate also led to higher N2O.

Nitrous oxide (N2O) is a potent greenhouse gas emitted during wastewater nitrification and denitrification. Batch nitrification with enriched nitrifying sludge and municipal wastewater was conducted in a laboratory reactor (working volume: 0.5 L) to investigate the impacts of organic components on N2O emissions at different aeration rates (10 and 20 mL/min) and NH4+-NNH4+-N concentrations (25, 50, and 100 mg/L). Maximum NH4+-NNH4+-N removal efficiencies reached 95 and 99% at the 10 and 20 mL/min aeration rates, respectively. At the 10 mL/min aeration rate, cumulative N2O-N emissions reached 0.44, 1.74, and 2.89 mg, while 0.79, 2.80, and 3.79 mg N2O-N were emitted at the 20 mL/min aeration rate with NH4+-NNH4+-N concentrations of 25, 50, and 100 mg/L, respectively. N2O emission yields (kg N2O-N per kg processed NH4+-NNH4+-N) were 0.039–0.076 and 0.064–0.109 at the 10 and 20 mL/min aeration rates, respectively, whereas the yields during nitrification without organics were 0.016–0.058 and 0.029–0.088 under the same experimental conditions. Overall, the municipal wastewater containing organics produced greater N2O emissions and yield than the wastewater without organics under the same operating conditions.