[Effect of C/N ratio on nitrous oxide production during denitrification with different electron acceptors].

The experiment investigated the nitrous oxide production under different C/N ratios during denitrification, taking nitrate and nitrite as electron acceptor respectively. Ethanol was selected as carbon source. The C/N ratios were 0, 1.2, 2.4, 3.5, 5.0 and 20 when nitrate was taken as electron acceptor and C/N ratios 0, 1.8, 2.4, 3.0, 4.3, 5.2, 6.6, 20.6 when electron acceptor was nitrite. The results indicated that: the optimum C/N ratio was 3.0 taking nitrite as electron acceptor and the N2O production was 0.044 mg x L(-1); the optimum C/N ratio was 5.0 taking nitrate as electron acceptor and the N2O production was 0.135 mg x L(-1) which was 3 times higher than that of nitrite as electron acceptor. Though the electron acceptor changed, the trend of N2O production was similar: when carbon source was badly insufficient, the production of N2O and denitrification rate were both quite small; the N2O production increased with the increasing of the quantity of carbon source; when the carbon source was excessive, the N2O production sharply raised. Consequently, compared to complete nitrification and denitrification, short-cut nitrification and denitrification could save 40% carbon source. Moreover, controlling C/N = 3 could reduce the production of N2O in short-cut nitrification.

[Effects of salinity concentration on N2O production during nitrification].

The experiment investigated the production and conversion rate of N2O during nitrification using saline sewage and municipal wastewater. Different kinds of sludge were used, domesticated by saline sewage influent (salinity 7.5 g/L) and municipal wastewater (salinity 0.1 g/L), respectively. The results showed that the production of N2O using saline sewage was 2.85 times higher than that using municipal wastewater. The production and conversion rate of N2O during nitrification under different salinities were also investigated. The results showed that the production of N2O was almost the same when salinity decreased from 7.5 g/L to 5.0 g/L, even 2.5 g/L. However, specific ammonia oxidation rate was increased with the decrease of salinity. The sudden increase of salinity, from 7.5 g/L to 10 g/L, resulted in the increase of N2O production and conversion rate but decrease of specific ammonia oxidation rate. Consequently, It is important to avoid the severe fluctuation of salinity resulted in the increase of N2O production and conversion rate.

[N2O emission and control in shortcut nitrification and denitrification and simultaneous nitrification and denitrification biological nitrogen removal systems].

SBR reactors were used to investigate the N2O emission in shortcut nitrification and simultaneous nitrification and denitrification (SND). Shortcut nitrification with nitrosation rate above 90% was realized by real-time control strategy. The N2O emission and variation of nitrosation rate were investigated under 4 DO levels (0.5, 1.0, 1.5, 2.0 mg/L). The results turned out that the optimal DO to maintain high nitrosation rate and minimum N2O emission was 1.5 mg/L and the N4O emission was 0.06 g per ammonium removed. The SBR filled with carbon fiber performed under low DO and pulse feeding. The SND rate was over 79% during the experiment. The N2O emission was studied under DO 0.2, 0.4, 1.0 and 1.5 mg/L. It turned out that the optimal DO was 1.0 mg/L and the N2O emission was 0.021 g per ammonium removed. Compared to the shortcut nitrification, the N2O emission of SND was 1/3 of the short-cut nitrification under optimal DO.