Achieving partial nitrification (PN) in low-strength wastewater is still a worldwide issue. In this study, conversion from nitrification to PN was successfully achieved with a self-sustained pH as low as 5.3 and a nitrite accumulation ratio (NAR) of 93.4 % by enriching novel acidic-tolerant functional flora. A strong positive correlation was observed between decreasing pH and NAR (R2 = 0.97). Even with 73.1 % reduction in influent ammonia (from 86.7 to 23.3 mg/L), high dissolved oxygen loading (4.5–5.3 mg/L), and extreme over-aeration, PN efficacy remained robust with the NAR consistently maintained at 90.6 ± 5.3 %. Over 180 days of continuous monitoring, novel ammonia-oxidizing bacteria (AOB) Candidatus Nitrosoglobus became the dominant nitrifying guild (1.65 %) with a specific growth rate of 0.091/day; however, traditional nitrifying bacteria exhibited impaired functionality and bacterial diversity was dramatically reduced. Amo abundance increased by 147 %, while Nxr in nitrifying bacteria dropped below detection limit, preventing complete nitrification. Upregulated electron transport chain genes enhanced electron flow, managing excess oxygen and effectively limiting harmful oxygen radical production, resulting in a desirable nitritation rate of 0.3 kg/m3·d with influent NH4+-N as low as 23.3 mg/L. These regulatory mechanisms boosted NH4+ oxidation efficiency, successfully unlocking scientific barriers associated with PN in ultralow-strength wastewater and laying the groundwork for future PN/A implementation.

中文翻译：

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解锁超低浓度废水中嗜酸微生物的部分硝化：长期研究和基因组见解


在低浓度废水中实现部分硝化（PN）仍然是一个世界性的问题。在本研究中，通过富集新型耐酸性功能菌群，成功实现了从硝化到PN的转化，自维持pH值低至5.3，亚硝酸盐积累率（NAR）达到93.4%。 pH 值下降和 NAR 之间存在很强的正相关性 (R2 = 0.97)。即使进水氨减少 73.1%（从 86.7 至 23.3 mg/L）、高溶解氧负荷（4.5–5.3 mg/L）和极端过度曝气，PN 功效仍然强劲，NAR 始终保持在 90.6 ± 5.3 %。经过180多天的连续监测，新型氨氧化细菌（AOB）Candidatus Nitrosoglobus成为硝化菌的优势菌群（1.65%），比生长率为0.091/天；然而，传统的硝化细菌表现出功能受损，细菌多样性急剧下降。 Amo 丰度增加了 147%，而硝化细菌中的 Nxr 降至检测限以下，阻止了完全硝化。上调的电子传递链基因增强了电子流，管理过量氧气并有效限制有害氧自由基的产生，从而实现理想的0.3 kg/m3·d的硝化率，进水NH4+-N低至23.3 mg/L。这些调节机制提高了 NH4+ 氧化效率，成功解锁了与超低浓度废水中 PN 相关的科学障碍，并为未来 PN/A 的实施奠定了基础。