曝气策略对膜面剪切力的影响机制及其优化

曝气冲刷是浸没式MBR工艺不同于常规活性污泥法工艺的关键特征，然而现行规范的曝气系统设计与运行比较粗放，缺乏气泡尺寸模拟优化方法。以可直接观测的工程规模 (500 m³·d⁻¹) 膜生物反应器为研究对象，对穿孔管角度进行了优化研究，并用群体平衡模型(Population Balance Model，PBM)模型模拟污泥混合液不同粘度下的内部气泡分布情况。结果表明：穿孔管角度垂直向下、60°、45°、30°、垂直向上在膜面产生的平均剪切力分别为1.74、1.46、1.19、1.38、1.67 Pa，这表明曝气角度最优为垂直向下。0.3%、0.5%和0.8%浓度的羧甲基纤维素钠(Carboxymethyl cellulose, CMC)下产生的平均剪切力分别是1.51、1.92、2.24 Pa，气泡直径逐渐增大。且气泡尺寸越大、流速越大，分布越均匀。基于0.3%、0.5% CMC的速度实验结果与 PBM模拟结果基本吻合。该研究结果可为MBR技术的工艺优化和系统控制方法提升提供参考。

Effect mechanism and optimization of aeration strategy on membrane surface shear stress

Aeration flushing is a key feature of the submerged membrane bioreactor (MBR) process that is different from the conventional activated sludge process. However, the current aeration system design and operation guidance are relatively extensive, and there is a lack of bubble size simulation optimization methods. Based on a scale of 500 m3·d−1 MBR that can be directly observed as the research object, the angle of the perforated tube was optimized and the Population Balance Model ( PBM ) was used to simulate the internal bubble distribution of the solution at different viscosities. Results showed that the average shear forces generated by the perforated tube with angles vertically down at 90 °, 60 °, 45 °, 30 °, and 0 ° on the membrane surface were 1.74,1.46,1.19,1.38,1.67 Pa, respectively, which indicated that the optimal aeration angle was vertically downwards. The average shear forces generated at 0.3%, 0.5% and 0.8% concentrations of carboxymethyl cellulose sodium (CMC) were 1.51, 1.92 and 2.24 Pa, respectively, and the bubble diameter gradually increased. The larger the bubble size was, the faster the flow velocity was, and the more uniform the distribution was. The results of velocity experiments conducted on 0.3% and 0.5% of CMC were consistent with those simulated by the PBM.The research results can provide reference for MBR process optimization and system control method improvement.