In this study, we investigated the sludge rising process during denitrification, especially its hydrodynamics, with both experiments and computational fluid dynamics (CFD) modeling. The rising process was observed and divided into three stages: bubble-forming, sludge particles rising with isolated bubbles, and sludge blanket rising. A new solid phase denoted as lighter sludge was introduced in the CFD simulation to bridge the gap between the simulation and the reality. We simulated the three-phase (wastewater, normal activated sludge, and lighter sludge) turbulent flow in the secondary clarifier. CFD simulation agreed with the experiments and math-model results. Lighter sludge dominated the effluent quality during the denitrification process. Sludge blanket rising started at scattered points in the bottom hopper. A 30-min window occurred between the rising of the sludge blanket and the worsening of effluent quality, which could be regarded as a critical time to prevent sludge from rising.

中文翻译：

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二级澄清池反硝化的污泥上升和临界时间预测：实验和计算流体动力学研究

在这项研究中，我们通过实验和计算流体动力学 (CFD) 模型研究了反硝化过程中的污泥上升过程，特别是其流体动力学。观察上升过程并将其分为三个阶段：气泡形成、污泥颗粒随孤立气泡上升和污泥层上升。在 CFD 模拟中引入了一种称为较轻污泥的新固相，以弥合模拟与现实之间的差距。我们模拟了二沉池中的三相（废水、普通活性污泥和较轻的污泥）湍流。CFD 模拟与实验和数学模型结果一致。在反硝化过程中，较轻的污泥支配着出水质量。污泥毯上升开始于底部料斗的分散点。