Investigation on N2O production and emission as a byproduct of different deammonification systems

整体研究的目的是调查与脱氨化过程（硝化，亚硝酸盐氧化，反硝化和厌氧氨氧化）相关的不同氮转化步骤的副产物氧化亚氮（N2O）的形成（第一年和第二年），并最终制定减少排放的措施（第三年）。在前两年，研究重点是在这些过程的典型边界条件下研究氧化亚氮的生物形成背景。具体而言，对有氧和缺氧过程分别考虑了相关的形成途径及其影响因素，描述了转化动力学，并评估了氧化亚氮形成的总体相关性。在高负荷过程中，亚硝酸盐的积累和特定基质如氧（硝化）和有机碳源（反硝化）的限制或可变可用性可以被证实是氧化亚氮形成的关键因素。结果进一步表明，即使具有有利于硝化过程N2O生成的操作条件，也可以限制但不能避免。在调查了运行条件对N2O形成的影响之后，研究将在第三年转向减少N2O排放的可能性。将专门针对脱氨化系统（高强度废水的部分硝化和厌氧氨氧化的组合）开发、测试和检查N2O最小化的操作策略。就上述调查所引致的下列工艺设计的技术及程序改变，将会确定减少氧化亚氮排放的潜力，并测试其可行性：a)利用扩散式供氧系统，避免普通曝气系统的剥离效应，以尽量减少气体输送；b)将N2O降解（反硝化成N2）整合到脱氨过程中，从而降低废气中N2O浓度；c)通过第一阶段（硝化）的适应性负荷控制最小化N2O形成潜力。该研究将在一个连续投料的两步好氧/缺氧实验室规模的工厂中实现。不同操作的实验室规模反应器连续运行较长时间（10个月），可以区分短期和长期影响，并包括不能在批量实验中测试的参数。将继续应用在项目头两年开发的测定N2O形成潜力（与N2O最终排放量不同）的方法。第三年结束时，将对在全规模工厂中应用相应措施可能减少的一氧化二氮排放进行估计。

The purpose of the overall study is to investigate the formation of nitrous oxide (N2O) as a byproduct of the different nitrogen conversion steps connected with the deammonification process (nitritation, nitrite oxidation, denitrification and anaerobic ammonium oxidation) (1st and 2nd year) and finally to develop measures for the reduction of emissions (3rd year). During the first two years, the research focus was to investigate the background of biological formation of nitrous oxide under the typical boundary conditions of these processes. Specifically relevant formation pathways and their influencing factors were considered separately for aerobic and anoxic processes, conversion kinetics were described and the overall relevance of nitrous oxide formation was evaluated. Accumulation of nitrite and limitation or variable availability of specific substrates like oxygen (nitrification) and organic carbon sources (denitrification) could be corroborated as crucial factors for nitrous oxide formation also in high-loaded processes. The results indicate furthermore that even with operational conditions that are regarded favorable for the process of nitritation N2O formation can be limited but not avoided. Following the investigations on the influence of operational conditions on N2O formation, the study will be oriented towards the possibilities to reduce the emission of N2O in the 3rd year. Operational strategies for N2O minimization will be developed, tested and examined specifically for deammonification systems (combination of partial nitritation and anaerobic ammonia oxidation for high-strength wastewater). For the following technical and procedural changes in process design, which result from the preceding investigations, the potential reduction of N2O emissions will be determined and the practicability tested:a) Minimization of the gas transfer by avoiding the stripping effect of common aeration systems making use of diffusion-based systems for oxygen supply;b) Integration of N2O degradation (denitrification to N2) into the deammonification process, hereby reduction of N2O concentration in the off-gas;c) Minimization of the N2O formation potential by adapted load control for the first stage (nitritation)The investigation will be realized in a continuously fed two-step aerobic/anoxic lab-scale plant. The continuous operation of differently operated lab-scale reactors for a longer period (10 months) enables differentiation of short- and long-term effects and inclusion of parameters that cannot be tested in batch experiments. Application of the methods for determination of the N2O formation potential (not identical with the final N2O emission) developed in the first two years of the project will be continued. The 3rd year will be concluded with an estimation of the potential reduction of N2O emissions by application of the respective measures in full-scale plants.