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

摘要：

N₂O是一种强效的温室气体,而污水生物脱氮过程是N₂O产生的一个主要人为来源。在本研究中,向生物处理出水中投加NH₄⁺、NH₂OH及NO₂^-,研究了NO₂^-对NH₄⁺及NH₂OH氧化过程中N₂O产生的影响。试验结果表明,NH₄⁺及NH₂OH氧化过程的最初30 min内(总反应时间180 min)产生的N₂O占总N₂O产生量的25%以上。在NH₄⁺或NH₂OH氧化完成前的30 min内,N₂O的净产生量仅有0.2 mg·L^-1。NH₂OH的氧化是短程硝化开始阶段产生N₂O的途径,此后NH₄⁺或NH₂OH氧化为AOB提供还原NO₂^-电子,引起的反硝化作用是产生N₂O的主要途径。在实际生活污水短程硝化试验过程中,由于部分COD的存在,在低氧条件下,可能会出现异养菌的反硝化作用。同时,由于氧气及NO₂^-对氧化亚氮还原酶(NOS)的抑制,使得在生活污水进行短程硝化时,N₂O的净产量比上述出水试验时增加了17%以上,总产量最高达到了11.07 mg·L^-1。这一途径对N₂O产生的贡献也是不容忽视的。

关键词: 短程硝化, NO₂^-, NH₂OH氧化, 异养反硝化