Advanced Water Management Centre-AWMC, The University of Queensland, Gehrmann Building 60, Research Road, St Lucia, Brisbane, QLD 4072, Australia.
Water Res. 2012 Oct 1;46(15):4832-40. doi: 10.1016/j.watres.2012.06.003. Epub 2012 Jun 15.
Acidic pH has previously been found to increase nitrous oxide (N₂O) accumulation during heterotrophic denitrification in biological wastewater treatment. However, the mechanism of this phenomenon still needs to be clarified. By using an enriched methanol utilizing denitrifying culture as an example, this paper presents a comprehensive study on the effect of pH (6.0-9.0) on N₂O reduction kinetics with N₂O as the sole electron acceptor, as well as the effect of pH on N₂O accumulation with N₂O as an intermediate of nitrate reduction. The pH dependency of nitrate and nitrite reduction was also investigated. The maximum biomass-specificN₂O reduction rate is higher than the corresponding maximum nitrate and nitrite reduction rates in the entire pH range studied. However, the maximum biomass-specific N₂O reduction rate is much more sensitive to pH variation outside of the optimal range (pH 7.5 to pH 8.0) than the maximum biomass-specific nitrate and nitrite reduction rates. The half-saturation coefficient of the N₂O reductase increased from 0.10 mg N₂O-N/L to 0.92 mg N₂O-N/L as pH increased from pH 6.0 to 9.0. At pH 6.0, approximately 20% and 40% of the denitrified nitrate accumulated as N₂O in the presence and absence of methanol (as an exogenous carbon source), respectively. However, at pH 6.5, these fractions decreased to 0% and 30%, respectively. No N₂O accumulation occurred at pH 7.0 to 9.0 independent of the availability of methanol. These results suggest that the competition for electrons among different nitrogen oxides reductases likely plays a role in N₂O accumulation at low pH conditions.
酸性 pH 值先前已被发现会增加异养反硝化过程中氧化亚氮（N₂O）的积累。然而，这一现象的机制仍需阐明。本文以甲醇利用型反硝化富集培养物为例，全面研究了 pH 值（6.0-9.0）对以 N₂O 为唯一电子受体的 N₂O 还原动力学的影响，以及 pH 值对 N₂O 积累的影响，其中 N₂O 是硝酸盐还原的中间产物。还研究了硝酸盐和亚硝酸盐还原的 pH 值依赖性。在整个研究的 pH 值范围内，最大生物量特异性 N₂O 还原率均高于相应的最大硝酸盐和亚硝酸盐还原率。然而，最大生物量特异性 N₂O 还原率对 pH 值在最佳范围（pH 7.5 至 pH 8.0）之外的变化更为敏感，而最大生物量特异性硝酸盐和亚硝酸盐还原率则不然。N₂O 还原酶的半饱和系数从 0.10 mg N₂O-N/L 增加到 0.92 mg N₂O-N/L，随着 pH 值从 6.0 增加到 9.0。在 pH 6.0 时，分别有 20%和 40%的反硝化硝酸盐以 N₂O 的形式积累，存在和不存在甲醇（作为外源碳源）的情况下。然而，在 pH 6.5 时，这两个分数分别减少到 0%和 30%。在 pH 7.0 至 9.0 时，无论甲醇是否存在，均未发生 N₂O 积累。这些结果表明，在低 pH 值条件下，不同氮氧化物还原酶之间争夺电子可能是 N₂O 积累的原因之一。
