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

Abstract

BACKGROUND: A large amount of N 2 O 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 N 2 O production characteristics in high-salt environment.RESULTS: This work merges three nitrous oxide (N 2 O) production pathways, namely ammonium-oxidizing bacteria (AOB) denitrification, incomplete hydroxylamine (NH 2 OH) oxidation and heterotrophic denitrification, into a multispecies activated sludge model to describe N 2 O 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 N 2 O production, while smaller amounts of N 2 O were generated by the AOB denitrification pathway (14.53-23.93%) and incomplete NH 2 OH oxidation pathway (3.54-7.75%).CONCLUSION: Denitrification on endogenous respiration will produce a small amount of N 2 O 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, N 2 O conversion (ratio of N 2 O production to total nitrogen removal) will increase with decreasing carbon source.

The effect of S/N ratio on NO and N2O accumulation during sulfide autotrophic denitrification

“…Figure 2 showed the changes of pH, ORP, S 2-, NO 3 and NO 2 under different S/N ratios. During SAD process, S 2was oxidized to S 0 and then to SO 4 2-, and the oxidation rate of S 2to S 0 (0.245-0.317) was much higher than that of S 0 to SO 4 2-(0.021-0.037) [7]. Thus, at the beginning, the concentration of S 2showed a sharply decrease, companied with nitrite declined, and nitrite accumulated simultaneous.…”

“…SAD has been extensive used in wet flue gas desulfurization and denitrification [2]. In SAD process, S 2is oxidized to SO 4 2-, and provide electron for denitrification (Equation ( 1)). Nitrate and nitrite work as electron acceptor and transformed to nitric oxide (NO), nitrous oxide (N 2 O) and finally to N 2 (Equation ( 2)) [3].…”

“…NO 3 -+ 2e -→ NO 2 -+ e -→ NO + e -→ 1/2 N 2 O + e -→ 1/2 N 2 (2) NO and N 2 O are unavoidable intermediate products of denitrification, and have environmental harm. NO could cause the hole in the ozone layer, and N 2 O has an extremely strong greenhouse effect [4]. Many researches have been focused on the production of N 2 O to minimize its emission.…”