Abstract:

Using domestic wastewater as influent and carbon fibre as biological carriers, the characteristics of SND(simultaneous nitrification and denitrification) process and N₂O emission were studied under different aeration intensity (30,20,10 L/h), with the DO(dissolved oxygen) concentration controlled at 1.5 mg/L by adjusting the ratio of N₂ and O₂. Hetertrophic and nitrifying bacteria conexisted in the biofilm, which are located in the outer and inner layers of the biofilm, respectively. The decrease of aeration intensity was beneficial to the proliferation of the external heterotrophic bacteria. With the aeration intensity was controlled at 30 L/h and 10 L/h, the removal efficiency of \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-\mathrm{N} in the SBBR system were more than 95% and 79.2%±1.6%, the SND efficiency was 46.2%±2.6% and 62.1%±2.3%, the N₂O yield was 6.25%±0.6% and 2.93%±0.43%, respectively. During the anoxic phase, the denitrification process and the accumulation of PHA (poly-β-hydroxyalkanoate) occurred simultaneously. In the following aerobic process, the PHA increased first and then decreased, which indicated that PHA could be used as internal carbon sources in the following denitrification process. Both the aerobic denitrification process of AOB and the denitrification process of denitrifying bacteria at the presence of lower oxygen led to the emissions of N₂O. The decrease of aeration intensity leads to a decrease in hydraulic shearing force, an increase in the anoxic range in the biofilm, and an increase in the N₂O residence time in the anoxic zone, which is beneficial to the denitrification reduction. As the aeration intensity decreased from 30 L/h to 10 L/h, the extracellular polymer (EPS) secretion decreased, and the PS/PN (polysaccharide/protein) decreased from 8.59 mg/mg to 6.58 mg/mg, resulting the reduction of the biofilm density, which created the favorable conditions for N₂O transferring into the biofilm to complete the reduction process.

Key words: simultaneous nitrification and denitrification, aeration intensity, N₂O, PHA, EPS

摘要：

以生活污水为处理对象，采用碳纤维填料制成序批式生物膜反应器（sequencing batch biofilm reactor，SBBR），采用N₂+O₂联合曝气的方式，通过改变N₂和O₂的比例，稳定系统内DO浓度为1.5 mg/L，考察不同曝气强度（30、20和10 L/h）下系统脱氮性能及N₂O释放特性。异养菌和硝化菌共生于生物膜内，异养菌位于外层，硝化菌位于内层，曝气强度降低有利于外部异养菌大量增殖，生物膜厚度增加。曝气强度为30 L/h和10 L/h条件下，SBBR系统\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-\mathrm{N}去除率分别为95%以上和79.2%±1.6%，同步脱氮效率分别为46.2%±2.6%和62.1%±2.3%，N₂O产率分别为6.25%±0.6%和2.93%±0.43%。缺氧阶段，反硝化过程和PHA（聚β–羟基烷酸酯）积累同时发生；好氧阶段，PHA呈先增加后减少的趋势。初始阶段增加的PHA为后续同步发生的反硝化过程提供了电子供体。AOB的好氧反硝化过程和异养菌反硝化过程均可导致N₂O的产生。曝气强度降低导致水力剪切力下降，生物膜内缺氧范围扩大，缺氧区N₂O停留时间延长，利于其反硝化减量。曝气强度由30 L/h降至10 L/h，微生物胞外聚合物（EPS）分泌减少，PS/PN（多糖/蛋白质）由8.59 mg/mg降至6.58 mg/mg,生物膜致密性降低，碳源和N₂O以扩散形式进入缺氧区域能力增强，N₂O释放量降低。

关键词: 同步硝化反硝化, 曝气强度, N₂O, PHA, EPS