作为世界上最为广泛应用的生物脱氮工艺类型，传统缺氧/好氧（A/O）生物脱氮工艺仍存在容积负荷低、曝气成本高等诸多不足。在提高容积负荷的基础上降低曝气量将是实现城市污水A/O工艺增效节能运行的关键。本论文充分挖掘了城市污水A / O工艺的负荷潜力，深入探讨了O段在微好氧条件（溶解氧（DO）0.5~1.0 mg·L-1）下运行时（即微好氧活性污泥工艺）的工艺特征和负荷潜力；依托自主研发的全过程氮转化活性分析方法全面比较了传统（好氧自养硝化、缺氧反硝化）和新型（好氧异养硝化、厌氧氨氧化、好氧反硝化）生物脱氮机制在生物脱氮两个关键节点的贡献，籍此阐明了城市污水A/O工艺增效节能优化过程中氮转化主要途径；依托高通量测序、克隆文库、定量PCR等现代微生态分析方法阐明了城市污水A/O工艺增效节能优化过程中优势氨氧化微生物的丰度、群落结构、优势物种类型的动态变化规律。研究结果将为城市污水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，具有重要的理论与实际意义。 论文取得如下重要研究结果： （1）建立了一种通过全过程氮转化活性水平阐明活性污泥氮转化主要途径的分析方法。以硝化污泥、厌氧氨氧化污泥和两株异养硝化菌作为研究对象，考察了DO、培养基和抑制剂（烯丙基硫脲（ATU）、氯酸钾、氯草定）对好氧自养氨氧化、好氧亚硝酸盐氧化，好氧异养氨氧化，厌氧氨氧化，好氧反硝化、缺氧反硝化等氮转化活性的影响。研究表明：将初始基质浓度/初始微生物浓度比（S0/X0）和反应时间设置在合理范围内时，可以将不同氮转化活性分析过程中生物合成作用的影响控制在较低水平；通过设置合理的DO环境和培养基类型可以区分大部分氮转化途径，但在好氧异养氨氧化活性测定时无法通过二者排除好氧自养氨氧化活性的影响；与其它抑制剂相比，ATU（10 mg·L-1）能够有效抑制自养硝化作用，同时对异养硝化活性等影响较小，能够用于控制好氧自养硝化作用，从而准确评价好氧异养硝化活性；基于上述结果，最终建立了基于DO、培养基、抑制剂添加等因素设计的全过程氮转化活性分析方法，并通过实际样品分析验证了该方法的准确性，该方法有效阐明了不同生物脱氮工艺的氮转化主要途径的差异。 （2）建立了一种关于活性污泥中可培养型好氧异养硝化菌的群落结构分析方法。以琥珀酸盐为碳源，从两种活性污泥中分离、纯化得到大量纯菌，通过分子鉴定、系统发育分析获得其分类信息，并全面考察了这些纯菌的好氧异养硝化能力。研究表明：两种污泥中获得的所有纯菌均具有显著的异养硝化能力（即均属于异养硝化菌），但污泥中异养硝化菌的活性与丰度并无显著的相关性；两种污泥中可培养型好氧异养硝化菌群落结构存在显著差异，充分反映了环境条件对污泥中好氧异养硝化菌群落结构的影响，为生物脱氮过程中控制和优化好氧异养硝化菌提供重要信息；基于上述结果，最终建立了基于琥珀酸盐为碳源的活性污泥中可培养型好氧异养硝化菌的“平板分离-纯化-分子鉴定“群落结构分析方法。 （3）首次证明了城市污水A/O工艺在极高容积负荷下长期稳定运行的可行性。在258天连续小试试验中，城市污水A/O工艺污泥浓度从3~5g·L-1最终提升到~10g·L-1，A/O池水力停留时间从12小时降至2小时，最终容积负荷高达~3.3kg COD·m-3·d-1和~0.6 kg NH4+-N·m-3·d-1（城市污水传统A/O工艺的3~4倍，与城市污水生物膜工艺或膜生物工艺相当），负荷提升过程中污染物去除效果显著、稳定（COD 95±3％、NH4 +-N 98±2％、TN 79±5％、TP 74±10％），与传统A/O工艺相比，城市污水高负荷A/O工艺曝气量可节省22％，占地面积节省~2/3，具有显著的增效节能效果。 （4）阐明了城市污水A/O工艺负荷优化过程中生物脱氮机制及其动态变化规律。基于全过程氮转化活性，在常规（0.9±0.1kg COD·m-3·d-1）、中高（2.4±0.1kg COD·m-3·d-1）和高（3.3±0.5 kg COD·m-3·d-1）负荷水平下城市污水A/O工艺的氮转化主要途径无显著性差异，即氨氧化过程主要途径为自养氨氧化和异养氨氧化共同作用，而产氮气过程主要途径为缺氧反硝化作用，而好氧反硝化或厌氧氨氧化对两个氮转化关键节点的贡献均较小；高通量测序结果表明三种负荷下污泥中好氧自养氨氧化细菌、亚硝化细菌和厌氧氨氧化菌的氮转化活性与其丰度存在显著的正相关关系（即活性水平可以反映其数量的变化）；克隆文库结果显示，负荷水平变化对好氧自养氨氧化菌群落结构影响较大，优势种从Nitrosomonas europaea（正常负荷，丰度61％）变为Nitrosomonas oligotropha （中高、高负荷下丰度分别为58%、81%）；同时可培养型好氧异养硝化菌优势种从 Agrobacterium tumefaciens（正常负荷，丰度42％）变为Acinetobacter johnsonii （高负荷，丰度52%）。 （5）首次发现城市污水微好氧活性污泥工艺存在非常显著的同时硝化-反硝化现象，并存在负荷提升潜力。在234天连续小试试验中，城市污水微好氧活性污泥工艺污泥膨胀严重，但仍通过较好的固液分离实现稳定运行，并节省~ 40% 曝气能耗（与城市污水传统A/O工艺相比），由于显著的同时硝化反硝化反应实现了污染物的高效、稳定去除（去除率：COD 94±3％，NH4+-N 99±2％，TN 64±12％，与A/O工艺相当），出水氨氧化产物以NO3--N为主，NO3--N、NO2--N浓度分别为10.8±2.3，0.9±0.3 mg·L-1；提高污泥浓度至~6g·L-1后，曝气池水力停留时间降低到3小时，污染物容积负荷达到2.3±0.4 kg COD·m-3·d-1和0.34±0.02 kg NH4+-N· m-3·d-1（是城市污水常规A/O工艺的2~3倍）。 （6）阐明了城市污水微好氧活性污泥工艺负荷优化过程中生物脱氮机制及其动态变化规律。基于全过程氮转化活性，在常规（0.9±0.1kg COD·m-3·d-1）和中高（2.3±0.4kg COD·m-3·d-1）负荷水平下城市污水微好氧活性污泥工艺的氮转化主要途径无显著性差异，并且与A/O工艺氮转化主要途径一致；高通量测序结果表明：常规负荷阶段污泥膨胀现象表现为丝状菌膨胀（丝状菌丰度达到16%，高于A/O工艺的1.4%），而中高负荷阶段污泥膨胀现象表现为粘性膨胀（丝状菌丰度仅为2.1%），好氧自养氨氧化菌和厌氧氨氧化菌的丰度差异与其活性差异相一致，反映了这两种氨氧化途径对氨氧化过程的不同贡献；克隆文库结果显示，负荷水平变化对好氧自养氨氧化菌群落结构影响较大，好氧自养氨氧化菌优势种从Nitrosomonas europaea（86％）变为Nitrosomonas oligotropha （53%）；同时可培养好氧异养硝化菌优势物种从 Agrobacterium tumefaciens（17％）变为Enterobacter asburiae （36%）。 （7）通过长期现场中试试验验证了通过高污泥浓度获得高容积负荷的可行性。在75天连续中试试验中（处理能力，1.3m3·d-1），制药废水（COD 3943±1302mg·L-1，NH4+-N 107±48 mg ·L-1）A/O工艺中试系统中污泥浓度从~0.6 g·L-1顺利提升到~8.0 g·L-1，A/O池水力停留时间从106小时降至70小时，最终容积负荷高达~2.2kg COD·m-3·d-1和~0.08 kg NH4+-N·m-3·d-1，整个负荷提升过程中污染物去除效果显著、稳定（COD 94±2％，NH4+-N 90±3％，TN 85±7％）。

Conventional biological nitrogen (N) removal (BNR) through the anoxic/oxic (A/O) process is widely employed in large-scale municipal wastewater treatment plants (WWTPs) worldwide. In most cases, the maximum chemical oxygen demand (COD) and NH4+-N loading rate (CODLR and NH4+-NLR) of the A/O process for municipal wastewater are just ~1.0 kg COD?m-3?d?1 and ~0.2 kg NH4+-N?m-3?d?1, respectively, which are far lower than those of MBRs or biofilm process. Furthermore, in municipal WWTPs using the conventional activated sludge process, aeration often represents 45~75% of the total energy consumption. Therefore, low loading rate and high energy consumption often limit the widespread application of the A/O process in municipal WWTPs. This doctoral thesis explored the potential of the A/O process for sewage treatment to achieve energy-saving and higher efficiency by optimizing its hydraulic retention time (HRT) and dissolved oxygen (DO) conditions, in addressing such limitations. To elucidate the microbial nitrogen-transformation mechanisms during the optimization periods, this doctoral research provides a method for the comprehensive N-transformation activity assessment. Using prepared nitrifying sludge, anaerobic ammonia oxidization (anammox) sludge and two heterotrophic ammonia oxidization bacterial (AOB) species as inocula, this study elucidated the effect of oxygen conditions, assay media, and selective metabolic inhibitors on various microbial N-transformation activities including aerobic chemolithotrophic ammonia and nitrite oxidization, aerobic heterotrophic ammonia oxidization, anammox, and aerobic and anoxic denitrification. The oxygen conditions and assay media effectively differentiated among almost all ammonia removal pathways except for separating aerobic chemolithotrophic ammonia oxidization from aerobic heterotrophic ammonia oxidization. A final allylthiourea (ATU) concentration of 10 mg ? L–1 was optimal for accurate determination of aerobic heterotrophic ammonia oxidization activity in the presence of aerobic chemolithotrophic AOB. Finally, this study developed a simple and reliable method to individually determine and compare the comprehensive N-transformation activity characteristics of several activated sludge samples from different origins, and to elucidate the major microbial N-transformation mechanisms for ammonia removal and N2 production. The second part of this thesis demonstrated and compared the community structures of culturable heterotrophic ammonia oxidization bacterial (HAOB) in two activated sludge samples after isolation on agar plates containing succinate as a selective carbon source, followed by purification, sequencing, and phylogenetic analysis. In total, 48 and 50 effective 16S rDNA sequences (representing >80% of the total colonies on an agar plate) were collected from the two samples, from which seven and eight operational taxonomic units (OTUs) were obtained, respectively. All OTU-identified isolates exhibited typical heterotrophic nitrification, either in this study or in previous reports, including four reported and eight previously undescribed HAOB species. The two culturable HAOB 16S rDNA sequence libraries exhibited significant differences in the diversity and relative abundance of culturable HAOB species according to their rarefaction curves, Shannon diversity indices, Chao1 estimator results, species composition, relative abundance of species, and phylogenetic trees. These differences fully reflect the effects of dissolved oxygen levels on the diversity of culturable HAOB communities in the two samples. The method developed here can be used to investigate the potential effects of environmental factors on culturable HAOB communities in environmental samples, which would provide important information for modeling, controlling and optimizing HAOB in biological nitrogen removal processes. Lab-scale experiments exploring the potential of the A/O process for sewage treatment were conducted to achieve energy saving and higher efficiency. A short HRT (~2 h for the A/O reactor), high mixed liquor suspended solids (MLSS, ~10 g?L?1), and high volumetric loading level (~3.3 kg COD?m?3?d?1 and ~0.6 kg NH4-N?m?3?d?1) in the A/O process for sewage treatment were achieved by enhancing biomass retention in the secondary clarifier (~4 h settling time). Over 258 days of continuous operation, with a decrease in HRT from 12 to 2 h, remarkable COD (95 ± 3%), NH4+-N (98 ± 2%), total nitrogen (TN, 79 ± 5%), and total phosphorus (TP, 74 ± 10%) removals were stably achieved, while the air requirement significantly decreased by 22%. The high-performance A/O process offers advantages over the conventional A/O process (6~8 h for A/O reactor, 3~5 g?L?1 MLSS, and ~1.0 kg COD?m?3?d?1) for sewage treatment in terms of its lower energy consumption, smaller footprint and reactor requirements. This study clarified the dominant N-transformation pathway and the dominant ammonia-oxidizing microbial species at three loading levels during A/O process optimization. Comprehensive N-transformation activity analysis showed that ammonia oxidization was performed predominantly by aerobic chemolithotrophic and heterotrophic ammonia oxidization rather than by anaerobic ammonia oxidization, whereas nitrogen gas (N2) production was performed primarily by anoxic denitrification rather than aerobic denitrification or anammox. High-throughput sequencing data demonstrated that the activities of AOB, nitrite-oxidizing bacteria, and AnAOB reflected their abundances in activated sludge. AOB ammonia monooxygenase subunit A (amoA) gene clone libraries revealed that the predominant AOB species in sludge samples shifted from Nitrosomonas europaea (61% at the normal loading level) to Nitrosomonas oligotropha (58% and 81% at the two higher loading levels). Following isolation and sequencing, the predominant culturable heterotrophic AOB in sludge shifted from Agrobacterium tumefaciens (42% at the normal loading level) to Acinetobacter johnsonii (52% at the highest loading level). These findings are very valuable for accelerating nitrification startup and ensuring stable N-removal during optimization of the A/O process for sewage treatment. On the other hand, this study investigated the long-term treatment performance of the microaerobic activated sludge (MAS) process for sewage treatment, which is characterized by high rates of simultaneous nitrification and denitrification reactions at 0.5~1.0 mg?L-1 dissolved oxygen. Good sludge/water separation and excellent pollutant removal performance (COD, 94± 3%; NH4+-N, 99 ± 2%; and TN, 64 ± 12%), with a short HRT (~3 h for the aeration tank), high MLSS (6.3±0.6g L?1), and higher volumetric loading (2.3±0.4 kg COD?m?3?d?1 and 0.34 ± 0.02 kg NH4-N?m?3?d?1) were stably achieved in the MAS system during its 234 days of continuous operation. The MAS process for sewage treatment offers advantages over the conventional A/O process, including 40% reduction in aeration energy consumption and 60% reduction in size requirements for the biological reaction unit. Moreover, we investigated the dominant N-transformation pathways, and key ammonia-oxidizing microbial species of the MAS process during sewage treatment at normal and high loading levels, using the conventional A/O process as a control. Consistent with the conventional A/O control system, ammonia oxidization in the MAS system occurred predominantly through aerobic chemolithotrophic and heterotrophic ammonia oxidization, which had significantly higher activities. The ubiquitous presence of heterotrophic AOB in both systems was demonstrated by isolation on agar plates, high-throughput sequencing data, and activity measurements. The abundances of AOB, anaerobic AOB, and heterotrophic AOB positively reflected the differences in their activities. The predominant AOB species shifted from Nitrosomonas europaea (61% and 86% for the conventional A/O control system and the MAS system at normal loading level, respectively) to Nitrosomonas oligotropha (53% in the MAS system at high loading level). In addition, the microaerobic conditions effectively triggered the predominance of denitrification, contributing to N2 production in the MAS system. Finally, a pilot-scale A/O process (with the treatment capacity of 1.3m3?d-1 wastewater) for pharmaceutical wastewater (COD 3943±1302 mg?L-1, NH4+-N 107±48 mg?L-1) treatment was conducted to testify the stratege of achieving a higher volumetric loading rate levels by enhancing biomass retention. Over 75 days of continuous operation, a higher MLSS (~8 g?L-1), a higher CODLR level (~2.2 kg COD?m?3?d?1), and remarkable COD (94 ± 2%), NH4+-N (90 ± 3%), TN (85 ± 7%) removals were stably achieved in the pilot-scale A/O process.