Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Sapporo 060-8628, Japan.
Water Res. 2013 Dec 1;47(19):7078-86. doi: 10.1016/j.watres.2013.07.055. Epub 2013 Oct 23.
Emission of nitrous oxide (N2O) during biological wastewater treatment is of growing concern since N2O is a major stratospheric ozone-depleting substance and an important greenhouse gas. The emission of N2O from a lab-scale granular sequencing batch reactor (SBR) for partial nitrification (PN) treating synthetic wastewater without organic carbon was therefore determined in this study, because PN process is known to produce more N2O than conventional nitrification processes. The average N2O emission rate from the SBR was 0.32 ± 0.17 mg-N L(-1) h(-1), corresponding to the average emission of N2O of 0.8 ± 0.4% of the incoming nitrogen load (1.5 ± 0.8% of the converted NH4(+)). Analysis of dynamic concentration profiles during one cycle of the SBR operation demonstrated that N2O concentration in off-gas was the highest just after starting aeration whereas N2O concentration in effluent was gradually increased in the initial 40 min of the aeration period and was decreased thereafter. Isotopomer analysis was conducted to identify the main N2O production pathway in the reactor during one cycle. The hydroxylamine (NH2OH) oxidation pathway accounted for 65% of the total N2O production in the initial phase during one cycle, whereas contribution of the NO2(-) reduction pathway to N2O production was comparable with that of the NH2OH oxidation pathway in the latter phase. In addition, spatial distributions of bacteria and their activities in single microbial granules taken from the reactor were determined with microsensors and by in situ hybridization. Partial nitrification occurred mainly in the oxic surface layer of the granules and ammonia-oxidizing bacteria were abundant in this layer. N2O production was also found mainly in the oxic surface layer. Based on these results, although N2O was produced mainly via NH2OH oxidation pathway in the autotrophic partial nitrification reactor, N2O production mechanisms were complex and could involve multiple N2O production pathways.
在生物废水处理过程中一氧化二氮（N2O）的排放引起了越来越多的关注，因为 N2O 是一种主要的平流层臭氧消耗物质和重要的温室气体。本研究测定了实验室规模的颗粒序批式反应器（SBR）在没有有机碳的条件下进行部分硝化（PN）处理合成废水时的 N2O 排放情况，因为 PN 工艺产生的 N2O 比传统硝化工艺多。SBR 的平均 N2O 排放率为 0.32 ± 0.17 mg-N L(-1) h(-1)，相当于输入氮负荷的 N2O 平均排放量为 0.8 ± 0.4%（转化的 NH4(+)的 1.5 ± 0.8%）。对 SBR 运行一个周期的动态浓度分布分析表明，在开始曝气时，废气中的 N2O 浓度最高，而在曝气期的最初 40 分钟内，出水中的 N2O 浓度逐渐增加，此后则降低。对一个周期内反应器中主要的 N2O 生成途径进行了同位素标记分析。在一个周期的初始阶段，羟胺（NH2OH）氧化途径占总 N2O 生成量的 65%，而在后期，NO2(-)还原途径对 N2O 生成的贡献与 NH2OH 氧化途径相当。此外，使用微传感器和原位杂交技术测定了从反应器中取出的单个微生物颗粒中的细菌及其活性的空间分布。部分硝化主要发生在颗粒的好氧表面层，该层中氨氧化细菌丰富。N2O 的产生也主要发生在好氧表面层。基于这些结果，尽管在自养部分硝化反应器中 N2O 主要通过 NH2OH 氧化途径产生，但 N2O 产生机制复杂，可能涉及多种 N2O 产生途径。
