关键词: 短程硝化, NO₂^-, NH₂OH氧化, 异养反硝化

Abstract:

Nitrous oxide (N₂O) is one of the most important greenhouse gases, about 265 times stronger than carbon dioxide (CO₂), and it may also destroy the ozone layer. In the biological wastewater treatment process, autotrophic nitrification has been thought to be the major source of N₂O production. So it becomes increasingly important to prevent N₂O emission from sewage treatment. In this study, by adding NH₄⁺, NH₂OH and NO₂^- to the effluent, the effect of NO₂^- on N₂O production by NH₄⁺ and NH₂OH oxidation during the nitritation process was investigated in a laboratory batch-scale system with activated sludge for treating domestic wastewater. Within the first 30 min of NH₄⁺ and NH₂OH oxidation process (total test time:180 min) N₂O accounted for more than 25% of the total production. As NH₄⁺ or NH₂OH was consumed completely, the amount of N₂O net production reduced to less than 0.2 mg·L^-1 in the last 30 min. Furthermore, the concentration of NO₂^--N could affect N₂O production. The increase of NO₂^--N would promote generation of N₂O. The maximum total N₂O net production was 6.86 mg·L^-1 when the concentration of NO₂^- was 60 mg·L^-1. NH₂OH oxidation played a key role in N₂O production at the very beginning of the experiment while nitrifier denitrification became a main pathway later. When the domestic sewage was treated under DO limited conditions, due to the presence of COD, there might occur heterotrophic denitrification during the aeration phase. However, oxygen and NO₂^- had strong inhibition on the activity of nitrous oxide reductase (NOS), consequently N₂O could not be reduced to N₂ completely. It led to more than 17% N₂O was produced and the maximum total net production reached 11.07 mg·L^-1. Hence, the contribution to N₂O produced by denitrification could not be ignored during the domestic wastewater treatment. Besides co-existence of NH₄⁺ and NH₂OH could significantly increase N₂O production and this process also emitted more N₂O when the concentration of NO₂^- was increased.

Key words: nitritation process, nitrite, NH₂OH oxidation, heterotrophic denitrification