Characteristics of nitrous oxide production under salt stress: a model study

BACKGROUND: A large amount of N₂O is often generated in the high‐salt wastewater nitrogen removal process, which is unfavorable to the environment, so it is necessary to build a model to describe the N₂O production characteristics in high‐salt environment. RESULTS: This work merges three nitrous oxide (N₂O) production pathways, namely ammonium‐oxidizing bacteria (AOB) denitrification, incomplete hydroxylamine (NH₂OH) oxidation and heterotrophic denitrification, into a multispecies activated sludge model to describe N₂O production under salt stress for the first time. The heterotrophic denitrification pathway was divided into two parts, namely denitrification on intracellular polymers and denitrification on endogenous respiration, and high‐salt inhibition terms were added to the intracellular polymer expressions on the heterotrophic denitrification pathway. The developed model was calibrated by a cycle running experimental case and validated by three single experimental cases, then assessed by two different sets of experimental data. The results indicated that the model reproduced experimentally measured data from six cases perfectly. The modeling results showed that the heterotrophic denitrification pathway (70.04–81.52%) played a significant role in N₂O production, while smaller amounts of N₂O were generated by the AOB denitrification pathway (14.53–23.93%) and incomplete NH₂OH oxidation pathway (3.54–7.75%). CONCLUSION: Denitrification on endogenous respiration will produce a small amount of N₂O with an initial carbon source; when there is no initial carbon source, it will be dominant. Owing to the competitive effects of heterotrophic denitrifying bacterial nitrogen reductase on electron donors, N₂O conversion (ratio of N₂O production to total nitrogen removal) will increase with decreasing carbon source. © 2019 Society of Chemical Industry