Effects of carbon source, C/N ratio, nitrate, temperature, and pH on N ₂ O emission and functional denitrifying genes during heterotrophic denitrification

The effects of operational parameters such as carbon source, C/N ratio, initial nitrate concentration, temperature, and pH value on heterotrophic denitrification and functional denitrifying genes were evaluated. When methanol was used as the sole carbon source, complete denitrification was performed in a short time without nitrous oxide (N ₂ O) emission. Complete denitrification was performed at high C/N ratios (5.14 and 12.85) and low initial nitrate concentrations (75.9 and 151.6 mg N L ⁻¹ ). The denitrification rate was not temperature-sensitive in the range of 25–35 °C, but tended to decrease at a low pH of 5–6. The relationships between N ₂ O emission and functional genes under various operational conditions were investigated by Pearson correlation and association network analyses. The C/N ratio was a key factor for N ₂ O emission during the heterotrophic denitrification process. This information on the denitrification performance and its association with functional gene dynamics under various operational conditions is useful for N ₂ O mitigation strategies for wastewater treatment processes.