In conventional activated sludge (CAS) systems and membrane bioreactors (MBR), aeration, mixing and filtration are affected by various properties of activated sludge (AS) and especially viscosity and morphological properties of flocs.

The aim of the present study was to understand the relationship between hydrodynamic conditions and AS floc size properties. Floc size distribution (FSD) measurements were performed in four systems showing different hydrodynamics: (i) a standard stirred reactor (SR), (ii) a pilot bubble column (BC), (iii) a full-scale aeration zone equipped with fine bubble diffusers, (iv) a full-scale filtration zone equipped with coarse bubble diffusers. The measurements were carried out on-site, using the mixed liquor from a full-scale MBR.

The FSD of the given activated sludge mainly depends on the average shear rate ($\dot{\gamma }$) and on the circulation time in the SR. To a lesser extent, local properties, such as maximal shear rate, also influence the FSD. In the same way, the main operating parameter governing the FSD in the BC was $\dot{\gamma }$. For a similar $\dot{\gamma }$, the flocs were slightly larger in the BC than in the SR. In addition, in the full-scale systems, for a similar $\dot{\gamma }$ estimated, the FSD characteristic diameters were lower in the filtration zone (with coarse bubbles) than in the aeration zone (with fine bubbles). The FSD in the aeration zone was well correlated with the FSD in the BC whereas the flocs were slightly smaller in the filtration zone than in the BC.

在常规的活性污泥（CAS）系统和膜生物反应器（MBR）中，曝气，混合和过滤会受到活性污泥（AS）的各种特性，尤其是絮凝物的粘度和形态特性的影响。

本研究的目的是了解流体动力学条件和AS絮体尺寸特性之间的关系。絮凝尺寸分布（FSD）测量在显示不同流体动力学的四个系统中进行：（i）标准搅拌反应器（SR），（ii）中试鼓泡塔（BC），（iii）配有精馏塔的全规模曝气区气泡扩散器，（iv）配备粗气泡扩散器的全尺寸过滤区。使用来自全尺寸MBR的混合液在现场进行测量。

给定活性污泥的FSD主要取决于平均剪切速率（$\dot{\gamma }$）以及SR中的循环时间。在较小程度上，局部特性（例如最大剪切速率）也会影响FSD。同样，控制卑诗省消防处的主要操作参数是$\dot{\gamma }$。对于类似$\dot{\gamma }$，在BC中，絮凝物比SR中的絮凝物稍大。另外，在满量程系统中，对于类似$\dot{\gamma }$据估计，FSD在过滤区（带有粗气泡）的特征直径要比曝气区（带有细气泡）的直径小。曝气区的FSD与BC的FSD相关性很好，而絮凝区的絮凝物比BC小。