新型污水生物脱氮工艺中氧化二氮、亚硝胺及其前驱物的产生、转化机制及排放控制技术研究

The biological nitrogen removal from sewage is a chain reaction converting organic and ammonia nitrogen into nitrogen gas, which involved various microbial enzymes as well as nitrogenous compounds. Recently lots of achievement of innovative technologies based on autotrophic biological nitrogen removal processes have been obtained on the enhancement of nitrogen removal efficiency and reduction of cost and energy consumption. However, little concern had been given to the potential environmental impacts of these technologies, such as generation, convertion and discharge of nitrous oxide and nitrosamines which could do great harm to environment and public health. This project will take nitrous oxide, nitrosamines and their precursors into account for comprehensive evaluation on innovative autotrophic biological technologies for nitrogen removal, including short-cut nitrification and denitrification, SHARON-ANAMMOX, and hydrogenotrophic denitrification. The crucial factors and mechanisms that affect the generation and conversion of the two kinds of substances will be investigated in different processes and operating conditions. The main nitrosamine precursors will be discerned. The functional genomes and microbial community structures that determine the converting pathway of two kinds of substances will be revealed by GeneChip and Illuminia sequencing. The expressions of functional genomes will be quantificationally monitored by reverse transcription- quantitative polymerase chain reaction at different operating conditions, thereby the microbiological mechanism would be revealed from these studies. Based on this study, the guidance will be offered for technology selection as well as operation optimization of innovative biological nitrogen removal technologies with discharge control of nitrous oxide, nitrosamines and precursors.

污水生物脱氮是由多种微生物参与的连续链式反应过程，从氨氮转化为硝态氮并最终转化成氮气的过程中可能产生多种中间产物。近年来研究者开发的各种新型自养生物脱氮技术在提高脱氮效率、降低能耗和运行成本等方面取得大量成果，但对其过程中可能产生或转化的含氮有害物质的关注尚不足。本课题拟针对两类危害较大的含氮有害物质，即释放到气相中氧化二氮和随液相排放的亚硝胺及其前驱物，利用GC，UPLC-MS/MS、同位素标记法研究其在不同自养生物脱氮工艺和运行条件下的产生和转化机制、关键因素及其相互间影响；采用“基因芯片”和“高通量测序”等技术识别相关功能基因和微生物群落特征；利用“逆转录-定量PCR”定量考察功能基因表达水平的变化规律，揭示生成两类物质的微生物学机理。通过本课题研究，将完善现有生物脱氮技术的综合评价标准，从氧化二氮、亚硝胺及其前驱物减量控制的角度，为污水处理生物脱氮工艺的选择和优化运行提供理论依据。

新型自养生物脱氮技术，例如厌氧氨氧化和氢自养反硝化工艺，在提高脱氮效率、降低能耗和运行成本等方面取得大量成果，但对其过程中可能产生或转化的含氮有害物质的关注尚不足。本课题针对两类危害较大的含氮有害物质，即释放到气相中N2O和含氮消毒副产物前体物，研究其在自养生物脱氮工艺运行中的产生和释放、关键因素及其微生物机理。氢自养反硝化工艺中pH和温度是影响NO3-还原、NO2-和N2O积累的关键因素，pH为6.0时，NO3-还原速率降低为0.50 kgN/(kgMLSS·d)，积累NO2-和N2O浓度最高，与初始TN比例分别为34.9%和15.2%。通过构建包含电子竞争过程的氢自养反硝化动力学模型，研究氢气供给速率的影响，结果表明，随着氢气供给速率的降低，各氮氧化物的还原速率均降低，同时氮氧化物还原酶之间电子分配发生变化，NO3-还原酶消耗电子的比例增加，NO2-还原酶消耗电子的比例变化较小，而N2O还原酶消耗电子的比例减少。表明当氢气供给不足时，电子竞争加剧，可导致N2O释放增加。厌氧氨氧化工艺中N2O的释放占总氮去除量（∆N2O/∆TN）比例为0.55~1.43%，含氮消毒副产物二氯乙腈和三氯硝基甲烷的前体物中的氮占进水总氮0.14%±0.03%，可溶性微生物副产物荧光峰的荧光强度与三氯硝基甲烷的生成潜能之间为正相关关系，可能是重要的含氮前体物。N2O最高积累浓度和总氮去除量、亚硝氮去除量呈正相关关系，温度降低导致厌氧氨氧化反应中N2O释放减少。一体式亚硝化-厌氧氨氧化工艺中，曝气模式、亚硝氮和碳源对N2O释放存在影响，同时调控氮循环基因转录水平。连续曝气实验中，N2O释放系数为1.02%，连续曝气实验中N2O比净产生速率低于间歇曝气运行的曝气阶段和非曝气阶段，然而好氧氨氧化菌的与N2O生成相关的氮循环基因hao和nirK的转录水平在间歇曝气实验和连续曝气实验中没有呈现显著差异。本课题完善了现有生物脱氮技术的综合评价标准，从氧化二氮、含氮消毒副产物前体物减量控制的角度，为污水处理生物脱氮工艺的选择和优化运行提供理论依据。