Nitrite effect on nitrous oxide emission from denitrifying activated sludge

摘要

Laboratory-scale experiments were conducted to examine the N_2O emission during the denitrification process. For each of the 6 runs carried out, synthetic effluent was fed in a 10 1 batch mixed liquor to investigate the effect of nitrite on N_2O emission and Helium was continuously bubbled through the reactor at constant rate (0.12 l/min) to favour N_2O transfer and detection. An increasing COD/NO_3~--N influent ratio from 3 to 7 was firstly applied (runs 1-3). Secondly, NO_2~- pulse additions were performed during run 4 and 5(10 and 20 mg N/l, respectively). Finally, the reactor was fed with influent containing both NO_2~- and NO_3~-. We showed that N_2O emission was detected shortly after NO_2~- accumulation, few minutes after the substrate feeding. The highest emission occurred at the lower COD/NO_3~--N ratio (=3) and at the higher NO_2~- addition (20 mg N/l). In addition, the higher nitrogen conversion to N_2O gas (14.4%) was obtained with an influent containing initially both NO_2~- and NO_3~-. Our results suggest a direct effect of the NO_2~- concentration on the N_2O emission. We have also confirmed the inhibitory effect of NO_2~- concentration on N_2O reduction.