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<p>Sludge bulking is a major challenge in activated sludge systems, closely related to dissolved oxygen as well as sludge loading. By managing appropriate sludge loads (0.20–0.22&#xa0;kg COD/(kg MLSS·d)), this research explored the effects of dissolved oxygen (DO) regulation on the anoxic/oxic (A/O) process. The results demonstrated that low DO condition (0.09–0.45&#xa0;mg/L) led to sludge bulking and a reduction in NH<sub>4</sub><sup>+</sup>-N removal performance. The DSVI of sludge rose from 92.3&#xa0;mL/g to 210.1&#xa0;mL/g. The NH<sub>4</sub><sup>+</sup>-N removal performance was improved under high dissolved oxygen condition (1.60–4.13&#xa0;mg/L), but the sludge settling performance remained poor. The extracellular protein concentrations in low DO bulking sludge and high DO bulking sludge are significantly higher than that in non-bulking sludge. Tryptophan-like protein served as a major protein constituent of the EPS. Moreover, compared to non-bulking sludge, the filamentous bacteria abundance was significantly higher in low DO bulking sludge, including norank<i>_Saprospiraceae</i>, norank<i>_ Caldilineaceae</i>, and <i>Anaerolineaceae</i>. Slow changes in extracellular protein concentration and filamentous bacteria abundance are the main factors making it difficult for DO regulation to quickly improve sludge settleability.</p> Graphical Abstract <p></p>

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Effects of Increasing Dissolved Oxygen on Sludge Bulking and Nitrogen Removal Performance under High Sludge Loading Conditions

  • 期刊论文

  • 发表日期：

    2025年8月11日

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  • Zhaoming Zheng,
  • Jiaxi Wang,
  • Jun Li,
  • Zehao Zhang,
  • Peng Tang,
  • Yuxin Geng

摘要

Sludge bulking is a major challenge in activated sludge systems, closely related to dissolved oxygen as well as sludge loading. By managing appropriate sludge loads (0.20–0.22 kg COD/(kg MLSS·d)), this research explored the effects of dissolved oxygen (DO) regulation on the anoxic/oxic (A/O) process. The results demonstrated that low DO condition (0.09–0.45 mg/L) led to sludge bulking and a reduction in NH4+-N removal performance. The DSVI of sludge rose from 92.3 mL/g to 210.1 mL/g. The NH4+-N removal performance was improved under high dissolved oxygen condition (1.60–4.13 mg/L), but the sludge settling performance remained poor. The extracellular protein concentrations in low DO bulking sludge and high DO bulking sludge are significantly higher than that in non-bulking sludge. Tryptophan-like protein served as a major protein constituent of the EPS. Moreover, compared to non-bulking sludge, the filamentous bacteria abundance was significantly higher in low DO bulking sludge, including norank_Saprospiraceae, norank_ Caldilineaceae, and Anaerolineaceae. Slow changes in extracellular protein concentration and filamentous bacteria abundance are the main factors making it difficult for DO regulation to quickly improve sludge settleability.

Graphical Abstract