城市污水管网中N2O的释放特征及产生机制研究

Wastewater sewer acted as huge biological reactor has been recognized by researchers. Nitrous oxide (N2O) can be emitted by nitrification and/or denitrification during wastewater transportation process. With popularization and application of wastewater sewer construction in a larger area, how to utilize sewer to remove nitrogen more efficiently, meanwhile, reduce N2O emission is a scientific problems to be focused and solved. In this work, we would like to study proceed of N2O production, emission rules and control factor in wastewater of sewer. Firstly, N2O emission shall be monitored during a long period with purpose to assess its amount and coefficient, and then demonstrate sewer is major/minor N2O emitter. Secondly, biofilm in sewer is incubated and sampled to study its characteristics, microorganism diversity and community characteristics by means of biological methods, such as PCR-DGGE, CLSM and FISH and so on. The results are analyzed to find relationship between community characteristics, microorganism diversity and N2O emission. Consequently, the mechanisms related to N2O production and emission can be deeply explored. Thirdly, indoor simulation experiment is conducted to study the effects of various factors on biofilm and N2O emission in order to propose optimum technological conditions and then build up simplified model of N2O emission amount in wastewater sewer. In conclusion, it will be helpful to expand new area of N2O study and reduce regional ammonia discharge and N2O emission.

污水管网作为一个巨大的生物反应器已被研究者所共识。污水在运输过程中由于微生物作用发生硝化/反硝化反应，使其成为N2O的排放源。随着我国管网建设的大面积推广、应用，如何利用其高效脱氮功能，同时又尽可能降低氧化亚氮（N2O）排放，是值得关注和解决的科学问题。本项目拟开展污水管网中N2O生成和释放规律及控制因子的研究。即：（1）通过对污水管网中N2O的长期监测，明确N2O的释放量和释放系数，论证污水管网是否为N2O的主要排放源；（2）通过培养和采集管道中生物膜，以PCR-DGGE、CLSM和FISH等生物学方法表征生物膜特性、微生物多样性及种群特征，结合N2O释放规律，深入探讨N2O的生成和释放机制；（3）通过室内模拟试验，深入研究各因子对生物膜和N2O释放的影响，逐步建立污水管网N2O释放量的简易模型，并筛选处理效果好和N2O释放低的工艺条件。本项目的完成有助于扩展N2O排放源研究的新领域。

项目首先对嘉兴市某段一级管网进行长达一年的N2O排放通量监测，以确定污水管网是否是一个N2O排放源。在室内通过一套密闭反应装置系统研究了转速与不同形态氮对N2O排放的影响，并分析污水微生物种群的多样性分布和群落结构的分布特征，分析了管网中功能性菌群的组成变化。为了真实反映污水管网生物膜的形成和特征，在嘉兴一级管网放置弹性填料培养生物膜，以对生物膜的组成变化与结构进行研究。.结果表明：（1）污水井全年各月的平均排放通量达到2600 μg/m2/h，随着污水井深度的增加，N2O排放通量会增加，可达3813 μg/m2/h。因此可明确城市污水管网是N2O的一个重要排放源。（2）室内污水管网模拟实验表明转速对N2O的释放影响较大，反应器内搅拌器不转状态反应产生N2O最多，而高速运行的反应器产生的N2O最少。（3）反应初始分别加入不同形态氮（硝酸钾、氯化铵和亚硝酸钠）对N2O产生影响较大，硝态氮、亚硝态氮和氨态氮的加入没有显著增加N2O的释放，氨态氮加入的反应产生N2O最大排放通量的时间晚于其它两种形态氮加入的反应。（4）通过高通量测序结果表明，与对照相比，NO3-加入量不同处理，管网沿程菌群丰度和多样性随反应有增加的趋势，污水管网内绝对优势菌门有变形杆菌、厚壁菌门以及拟杆菌门，其相对丰度分别呈增加、增加和减少的趋势。（5）对污水管网填料生物膜经过两个月的培养，因为污水流速较大，经观察没有形成有效生物膜，还在继续培养等待下一步的分析测定。