城市污水缺氧/好氧（A/O）生物脱氮工艺增效节能优化与脱氮机制研究

The conventional biological nitrogen removal process, i.e. the anoxic/oxic (A/O) process, is widely used in municipal wastewater treatment plants (WWTPs) worldwide as a means to control eutrophication in natural waterbodies. For a long time, some problems frequently accompanied with the wide application of conventional A/O process, including low organic loading rate, high energy consumption because of aeration, and so on. The maximum chemical oxygen demand loading rate (CODLR) and ammonia nitrogen loading rate (NH4+-NLR) levels of the conventional A/O process were just ~1.0 kg COD•m-3•d−1 and ~0.2 kg NH4+-N•m-3•d−1 for sewage treatment, which were far lower than MBRs or biofilm process. Our previous investigation achieved a short hydraulic retention time (HRT) (~2 h for the A/O reactor), high mixed liquor suspended solids (MLSS) (~10 g L−1), and high volumetric loading (~3.7 kg COD•m−3•d−1 and ~0.6 kg NH4-N•m−3•d−1) in the A/O process for sewage treatment. Furthermore, we demonstrated that microaerobic DO conditions in the O unit of the A/O process (referred to as the microaerobic activated sludge process in this study) achieved excellent simultaneous nitrification and denitrification reactions. In the last two decades, several novel N-transformation mechanisms, including aerobic heterotrophic ammonium oxidation, aerobic denitrification, and chemolithoautotrophic anaerobic ammonia oxidation (anammox) have drastically altered our understanding of the possible N-transformation pathways occurring in A/O process and its optimized types. The primary objectives of this study were as follows: (i) to determine and elucidate the dominant N-transformation pathway for ammonia oxidization and N2 production, and the key ammonia-oxidizing microbial species (i.e., the rate-limiting step of the BNR process) and its relative abundance in the conventional A/O process, and track their changes during A/O process optimization from the normal loading rate to the highest loading rate; (ii) to determine and elucidate the dominant N-transformation pathway for ammonia oxidization and N2 production, and the key ammonia-oxidizing microbial species and its relative abundance in the microaerobic activated sludge process, and track their changes during process optimization from the normal loading rate to the highest loading rate; (iii) to determine and elucidate the dominant N-transformation pathway for ammonia oxidization and N2 production, and the key ammonia-oxidizing microbial species and its relative abundance in the high-loading microaerobic activated sludge process, and track their changes during return ratio optimization from 20% to 300%; (iv) to determine and elucidate the dominant N-transformation pathway for ammonia oxidization and N2 production, and the key ammonia-oxidizing microbial species and its relative abundance in the high-loading anoxic/microaerobic (A/M) process, and track their changes during A;M volumetric ratio optimization from 0 to 1:9. The relative contribution of various N-transformation pathways to ammonia removal or N2 production can be determined and compared through comprehensive N-transformation activities. In this manner, the dominant N-transformation pathways for ammonia removal and N2 production can be elucidated. Furthermore, the rapid development of modern molecular biological techniques, such as quantitative polymerase chain reaction (qPCR), clone libraries, and high-throughput pyrosequencing in recent decades has enabled better determination of the presence, distribution, and population dynamics of ammonia-oxidizing microbial communities in BNR systems.

城市污水缺氧/好氧（A/O）生物脱氮工艺应用广泛、容积负荷低、运行成本高，申请人发现它可在3-4倍负荷下稳定运行并节省22%曝气量；O段在微好氧条件下运行时（即微好氧活性污泥工艺）同时硝化-反硝化反应显著，对A段反硝化的依赖下降。阐明A/O工艺优化过程中的生物脱氮机制需要全面、客观评价异养硝化、厌氧氨氨化、好氧反硝化等新机制的贡献。本项目将以城市污水为研究对象，以“传统A/O工艺负荷优化→微好氧活性污泥工艺负荷优化→高负荷微好氧活性污泥工艺运行参数优化→高负荷缺氧/微好氧工艺设计与运行参数优化”为主线层层推进研究，深入探讨城市污水A/O工艺多层次增效节能策略，重点聚焦、阐明不同优化阶段氮转化主要途径（氨氧化和产氮气）、优势氨氧化微生物的丰度、群落特征、优势物种类型等生物脱氮机制的动态变化，为城市污水A/O工艺增效节能工程实践中缩短硝化启动时间、实现脱氮效果稳定提供充分的理论支撑。

作为世界上应用最为广泛的城市污水生物脱氮工艺类型，缺氧/好氧（A/O）生物脱氮工艺存在容积负荷低、曝气成本高等诸多不足。.本项目致力于通过提高容积负荷（接近常规厌氧工艺）、降低曝气量（微好氧运行）和两者联合策略来最大程度地挖掘城市污水A/O生物脱氮工艺的增效节能潜力，沿着工艺研发主线“高负荷A/O→微好氧活性污泥（MAS）→高负荷MAS（H-MAS）→高负荷缺氧/微好氧（H-A/M）”层层深入，通过这些增效节能策略将城市污水A/O工艺处理能力（或容积负荷）提高到原来的3-7倍（相应大幅降低了投资成本和占地面积），同时曝气运行成本降低了20-40%，可通过简单调试或小规模技术改造工程即可实现，市场应用潜力巨大。基于理论分析和实验修正、优化了高膨胀污泥的斜板沉淀模型，解决了H-MAS和H-A/M工艺工程应用时二沉池高膨胀污泥固液分离难的瓶颈问题，形成了可指导实际生产的H-MAS-斜板沉淀工艺设计和运行参数。除有机物、氮、磷的同时高效去除外，H-A/M工艺还能节省50%有机物需求、减少75%剩余污泥量，是一个极有前景的生物脱氮除磷新工艺。.本项目系统调研了废水生物脱氮系统中异养硝化菌（HAOB）、生物强化除磷系统中聚磷菌（PAO）的多样性、丰度和活性检测方法现状，为后续机理研究提供了全面的信息；建立了一套全过程氮转化活性检测和微生态手段相结合的分析方法，阐明了不同增效节能策略中微生物氮转化主要途径和优势微生物种，为城市污水A/O工艺增效节能工程实践中缩短硝化启动时间、实现脱氮效果稳定提供了充分的理论支撑。本项目研究结果纠正了活性污泥法效率低下、城市污水A/O脱氮工艺A/O池HRT必须大于8 h等错误认识，发现了絮体污泥中微好氧同时硝化反硝化（此前仅在生物膜系统中观察到）、无预厌氧时缺氧反硝化聚磷、HAOB对氨氧化存在突出贡献等科学现象，丰富和完善了生物脱氮除磷机理，科学意义突出。