含氮污水的深度脱氮是一直是水环境污染治理面临的重要挑战，特别是针对高氨氮低C/N类污水，如厌氧发酵沼液、垃圾渗滤液等。生物脱氮技术因其能耗和运行成本低且无二次污染等显著优势，现已成为应用最广泛的污水脱氮技术。然而在处理高氨氮低C/N废水时，传统的硝化-反硝化生物脱氮技术虽然能实现脱氮，但存在曝气大能耗高和碳源消耗大等问题。厌氧氨氧化（Anammox）是在厌氧条件下以NO₂⁻-N作为电子受体直接去除NH₄⁺-N，是一种高效节能的新型生物脱氮技术，在高氨氮低C/N废水处理方面极具应用前景。然而Anammox工艺核心功能菌厌氧氨氧化菌（AnAOB）对环境条件敏感，活性易受到抑制；同时该工艺依赖的NO₂⁻-N底物难以稳定供给，且存在NO₃⁻-N副产物累积问题，制约了大规模化的推广应用。因此，完善生物脱氮技术意义重大。

鉴于铁矿物中铁元素可以通过多种机制参与和强化生物脱氮效能，并考虑到相比于其他铁矿物，施氏矿物（Sch）和磁性纳米施氏矿物（Fe₃O₄@Sch）作为亚稳态铁矿物在强化生物脱氮方面可能具有独特优势，有望强化Anammox过程以及诱导AnAOB发生Feammox。但目前关于Sch和Fe₃O₄@Sch强化生物脱氮，尤其是在强化高氨氮低C/N废水脱氮方面的研究还鲜有报道。为此，本研究在生物脱氮过程中引入亚稳态的Sch及其复合材料，探索其通过强化硝化-反硝化、Anammox及诱导Feammox，实现高氨氮低C/N废水的有效脱氮的可能性。主要结果如下：

（1）提出了Sch强化SBR活性污泥法对餐厨沼液废水（固液分离预处理后）的碳氮协同去除方法。结果表明，添加Sch有效促进了沼液废水中难降解有机物的降解转化，为微生物提供更多可利用的碳源，间接强化了反硝化过程。TN的去除效果提高了23%，实现了高氨氮低C/N废水生物脱氮体系中C、N协同去除。此外，添加Sch处理组中，污泥中微生物EPS含量显著增加，尤其是蛋白质组分，促进了污泥絮体聚集能力，增强了功能微生物的代谢活性。

（2）探究了Fe₃O₄@Sch对Anammox过程的驯化、启动过程的影响，并优化了Fe₃O₄@Sch添加量对Anammox体系的脱氮效果。添加Fe₃O₄@Sch驯化处理组中，尽管Anammox功能微生物丰度未显著增加，但TN去除率提高了16.84%，推测是体系中其他功能菌如OLB14通过提供Anammox反应底物（NO₂⁻-N）进而强化了脱氮效果。添加Fe₃O₄@Sch将Anammox启动期缩短了25%（10 d），并可以促进AnAOB在失活情况下的活性恢复及启动过程。此外，Fe₃O₄@Sch添加量在0.25~0.5 g/g MLVSS（以Fe计）时，对Anammox体系脱氮的强化效果为优。与对照组相比，TN去除率由64%增加至80%~83%，并以0.5 g/g MLVSS为最优，但Fe₃O₄@Sch过量也会抑制Anammox。

（3）构建了Fe₃O₄@Sch调控的Anammox、Feammox及铁自养反硝化(NDFO)耦合脱氮体系，并实现了对高氨氮低C/N废水的高效脱氮。经过长期驯化后，耦合体系对NH₄⁺-N及TN去除能力显著增加，进水NO₂⁻-N /NH₄⁺-N比值由1.2降低到1.0后（进水TN浓度为900 mg/L，负荷保持不变），TN去除能达到86%，优于单一Anammox体系（83%）；同时改善了Anammox体系NO₃⁻-N积累的问题（ΔNO₃⁻-N /ΔNH₄⁺-N值从0.26降低至0.17）。耦合体系降低了短程硝化NO₂⁻-N供给需求及NO₃⁻-N脱除的反硝化碳源消耗，能耗与碳源需求分别降低了10%和28%。运行稳定后，Anammox、Feammox和NDFO的脱氮贡献分别为79.4%、10.7%和9.8%。Brocadia sinica和Brocadia sapporoensis为体系中的主要功能菌，其相对丰度分别从11.43%和4.77%提高到了15.85%和5.69%，其中Brocadia sinica为潜在的Feammox功能菌。

综上，亚稳态的Sch在调控高氨氮低C/N废水生物脱氮方面具有突出优势。本研究通过在异养与自养生物脱氮过程中分别添加Sch和Fe₃O₄@Sch，对废水中碳氮协同去除均表现显著效果，特别是调控Anammox与Feammox等自养脱氮过程。本研究将为铁矿物调控多途径生物脱氮的协同增效及其在高氨氮低C/N废水的深度处理中提供参考。

Deep nitrogen removal from nitrogen-containing wastewater has always been a critical challenge in water pollution control, particularly for high-ammonia and low C/N ratio wastewater such as anaerobic fermentation biogas slurry and landfill leachate. Biological nitrogen removal technologies, owing to its advantages of low energy consumption and operational costs, as well as absence of secondary pollution, have become the most widely applied methods. However, when treating high-ammonia and low C/N wastewater, traditional nitrification-denitrification processes, while effective, face issues such as high aeration demand and excessive carbon consumption. Anaerobic ammonium oxidation (Anammox), a novel and energy-efficient biological nitrogen removal technology, directly converts NH₄⁺-N using NO₂⁻-N as an electron acceptor under anaerobic conditions, showing great potential for high-ammonia and low C/N wastewater treatment. Nevertheless, the core functional bacteria of Anammox - anaerobic ammonium-oxidizing bacteria (AnAOB) - are environmentally sensitive and prone to activity inhibition. Additionally, the process relies on unstable NO₂⁻-N substrate supply and faces challenges with NO₃⁻-N byproduct accumulation, limiting its large-scale application. Therefore, improving biological nitrogen removal technologies is of great significance.

Considering that iron species in iron minerals can participate in and enhance biological nitrogen removal through multiple mechanisms, and given that compared to other iron minerals, schwertmannite (Sch) and its magnetic nanocomposite (Fe₃O₄@Sch), as metastable iron minerals, may possess unique advantages in enhancing biological nitrogen removal—potentially strengthening the Anammox process and inducing Feammox in AnAOB—there is currently limited research on Sch and Fe₃O₄@Sch for enhanced biological nitrogen removal, particularly in the treatment of high-ammonia and low C/N ratio wastewater. Therefore, this study introduces metastable Sch and its composite materials into biological nitrogen removal processes to explore their potential in achieving efficient nitrogen removal from high-ammonia and low C/N ratio wastewater by enhancing nitrification-denitrification, Anammox, and inducing Feammox. The main findings are as follows:

(1) This study proposes a novel approach utilizing Sch to enhance the synergistic removal of carbon and nitrogen in food waste anaerobic digestion effluent (after solid-liquid separation pretreatment) via SBR activated sludge process. The results demonstrate that Sch addition effectively promoted the degradation and transformation of refractory organic matter in the digester effluent, thereby providing additional bioavailable carbon sources for microorganisms and indirectly strengthening the denitrification process. Notably, the total nitrogen (TN) removal efficiency was improved by 23%, achieving coordinated C/N removal in the high-ammonia low C/N ratio wastewater treatment system. Furthermore, in Sch-amended reactors, a significant increase in extracellular polymeric substances (EPS) content was observed, particularly in protein components, which enhanced sludge flocculation capacity and improved the metabolic activity of functional microorganisms.

(2) This study investigated the effects of Fe₃O₄@Sch on the acclimation and start-up processes of Anammox, while optimizing its dosage for enhanced nitrogen removal. In Fe₃O₄@Sch-amended systems, although the abundance of Anammox functional microorganisms showed no significant increase, the total nitrogen (TN) removal efficiency improved by 16.84%. This enhancement is presumably attributed to other functional bacteria (e.g., OLB14) that may supply NO₂⁻-N as substrates for Anammox reactions. Notably, Fe₃O₄@Sch addition shortened the Anammox start-up period by 25% (10 days) and facilitated activity recovery of inhibited AnAOB during reactor restart. Optimal Fe₃O₄@Sch dosage was determined to be 0.25-0.5 g/g MLVSS (Fe basis), under which TN removal efficiency increased from 64% (control) to 80%-83%, with 0.5 g/g MLVSS showing peak performance. However, excessive Fe₃O₄@Sch addition exhibited inhibitory effects on Anammox activity.

(3) This study successfully constructed a Fe₃O₄@Sch-regulated integrated nitrogen removal system coupling Anammox, Feammox and iron-mediated autotrophic denitrification (NDFO) that achieved highly efficient treatment of high-ammonia low C/N ratio wastewater. After long-term acclimation, the coupled system demonstrated significantly enhanced NH₄⁺-N and total nitrogen removal capacities, achieving 86% TN removal efficiency when the influent NO₂⁻-N/NH₄⁺-N ratio was reduced from 1.2 to 1.0 while maintaining 900 mg/L TN concentration, outperforming conventional Anammox systems (83%) and effectively alleviating NO₃⁻-N accumulation by decreasing ΔNO₃⁻-N/ΔNH₄⁺-N ratio from 0.26 to 0.17. The integrated system reduced NO₂⁻-N supply demand for partial nitrification by 15%, decreased carbon requirement for NO₃⁻-N removal by 28%, and lowered overall energy consumption by 10% compared to single-process systems, with stable operation analysis revealing nitrogen removal contributions of 79.4% from Anammox, 10.7% from Feammox and 9.8% from NDFO. Microbial community analysis showed enrichment of key functional species including Brocadia sinica (increased from 11.43% to 15.85%) and Brocadia sapporoensis (increased from 4.77% to 5.69%), with Brocadia sinica identified as a potential Feammox-performing bacterium exhibiting dual metabolic capability, while the system maintained excellent operational stability for over 120 days with sludge volume index consistently below 50 mL/g, demonstrating the first successful Fe₃O₄@Sch-mediated tri-pathway synergistic nitrogen removal with quantitatively resolved metabolic contributions and practical energy/carbon savings validated by comprehensive mass balance analysis.

In summary, metastable schwertmannite (Sch) exhibits outstanding advantages in regulating biological nitrogen removal from wastewater with high ammonia nitrogen and low C/N ratios. In this study, the addition of Sch and Fe₃O₄@Sch during heterotrophic and autotrophic nitrogen removal processes, respectively, demonstrated significant effects on the synergistic removal of carbon and nitrogen from wastewater, particularly in enhancing autotrophic nitrogen removal pathways such as Anammox and Feammox. This research provides valuable insights into the synergistic effects of iron minerals in regulating multi-pathway biological nitrogen removal and their application in advanced treatment of high-ammonia, low C/N wastewater.

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