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<p>The ammonium concentration in the biogas slurry after anaerobic digestion of municipal residual sludge is very high, it is difficult to be treated effectively by traditional methods. This study proposed a method for removing high concentrations of nitrogen via iron cycling driven by intermittent aeration (20&#xa0;min every 9&#xa0;days at 10 vvm (air volume/culture volume/min). Results demonstrated that Fe(II) in slurry decreased rapidly after aeration (3.4&#xa0;mg Fe(II)/(L·min)), then it rose again after stopping aeration, resulting in the cycle of indigenous iron of slurry. The product of Fe(II) oxidation during aeration was confirmed to be Fe(OH)<sub>3</sub> through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), which was the least crystalline and the most reactive Fe(III) (hydr-)oxide, enabling Fe(III)-ammonium oxidation (Feammox) effectively. The total nitrogen (TN, 302.6&#xa0;mg/L) removal efficiency reached 82.1% after 30&#xa0;days in the intermittent aeration group, significantly higher than that in the anoxic control group (30.1%) (<i>p</i> = 0.032). Microbial analysis revealed that iron-reducing bacteria, including <i>Pseudomonas</i> (5.1%), <i>Thiobacillus</i> (1.7%), and <i>Geobacter</i> (0.4%), were enriched in the aeration group, while nitrifying and Anammox bacteria (e.g., <i>Nitrospina</i>, <i>Nitrosospira</i>) were not detected. Additionally, compared to the control, the electron transfer capacity after experiment in the aeration group increased by more than 50%. Further experiments with higher TN (714.9 ± 12.1&#xa0;mg/L) validated the methods robustness, achieving 77.8% TN removal. The above results indicated that intermittent aeration can trigger the iron cycle, enrich iron-reducing bacteria and enhance nitrogen removal. This study highlighted intermittent aeration as a strategy for treating low C/N biogas slurry.</p> Graphical abstract <p></p>

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Study on the impact and mechanism of iron cycling induced by intermittent aeration on nitrogen removal in biogas slurry

  • 期刊论文

  • 发表日期：

    2025年12月11日

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  • Changhui Hu,
  • Xiangyu Huang,
  • Jihua Wang,
  • Xinyi Wu,
  • Dandan Yan,
  • Xiangshan Zeng,
  • Jinlai Yuan,
  • Hailei Su,
  • Luntao Wu,
  • Yang Wang,
  • Wanyu Yang,
  • Xiaotan Zhou,
  • Ping Xiang,
  • Yafei Yang

摘要

The ammonium concentration in the biogas slurry after anaerobic digestion of municipal residual sludge is very high, it is difficult to be treated effectively by traditional methods. This study proposed a method for removing high concentrations of nitrogen via iron cycling driven by intermittent aeration (20 min every 9 days at 10 vvm (air volume/culture volume/min). Results demonstrated that Fe(II) in slurry decreased rapidly after aeration (3.4 mg Fe(II)/(L·min)), then it rose again after stopping aeration, resulting in the cycle of indigenous iron of slurry. The product of Fe(II) oxidation during aeration was confirmed to be Fe(OH)3 through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), which was the least crystalline and the most reactive Fe(III) (hydr-)oxide, enabling Fe(III)-ammonium oxidation (Feammox) effectively. The total nitrogen (TN, 302.6 mg/L) removal efficiency reached 82.1% after 30 days in the intermittent aeration group, significantly higher than that in the anoxic control group (30.1%) (p = 0.032). Microbial analysis revealed that iron-reducing bacteria, including Pseudomonas (5.1%), Thiobacillus (1.7%), and Geobacter (0.4%), were enriched in the aeration group, while nitrifying and Anammox bacteria (e.g., Nitrospina, Nitrosospira) were not detected. Additionally, compared to the control, the electron transfer capacity after experiment in the aeration group increased by more than 50%. Further experiments with higher TN (714.9 ± 12.1 mg/L) validated the methods robustness, achieving 77.8% TN removal. The above results indicated that intermittent aeration can trigger the iron cycle, enrich iron-reducing bacteria and enhance nitrogen removal. This study highlighted intermittent aeration as a strategy for treating low C/N biogas slurry.

Graphical abstract