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

总体研究的目的是调查与脱氨过程(亚硝化、亚硝酸盐氧化、反硝化和厌氧氨氧化)相关的不同氮素转化步骤的副产品氧化亚氮(N2O)的形成(第1年和第2年)，并最终制定减排措施(第3年)。在最初的两年里，研究的重点是在这些过程的典型边界条件下考察一氧化二氮生物形成的背景。具体地说，分别考虑了好氧和缺氧过程中相应的生成途径及其影响因素，描述了转化动力学，并评价了一氧化二氮生成的总体相关性。亚硝酸盐的积累和特定底物如氧气(硝化作用)和有机碳源(反硝化作用)的限制或变化的有效性可以被证实为在高负荷过程中也是一氧化二氮形成的关键因素。结果进一步表明，即使在被认为有利于亚硝化过程的操作条件下，N2O的生成也可以受到限制，但不能避免。在考察了运行条件对N2O生成的影响后，本研究将着眼于在第3年减少N2O排放的可能性。将专门为脱氨系统(高浓度废水的部分亚硝化和厌氧氨氧化的组合)制定、测试和研究最大限度减少N2O的操作策略。对于工艺设计中的以下技术和程序变化，将确定减少N2O排放的潜力，并测试其实用性：a)通过避免使用基于扩散的供氧系统的普通曝气系统的汽提效应，最大限度地减少气体转移；b)将N2O降解(反硝化为氮气)整合到脱氨过程中，从而降低尾气中的N2O浓度；c)通过对第一阶段(亚硝化)进行适当的负荷控制，最大限度地减少N2O的生成潜力。不同操作的实验室规模反应堆连续运行更长时间(10个月)，能够区分短期和长期影响，并包括无法在批量实验中测试的参数。将继续应用项目头两年开发的确定N2O生成潜力(与最终N2O排放量不同)的方法。在第三年结束时，将估计通过在全规模工厂中应用相应措施来减少N2O排放的潜力。

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.