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Porosity and structure of alum coagulation and activated sludge flocs.

机译：明矾凝结和活性污泥絮凝物的孔隙率和结构。

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Knowledge of floc porosity and structure is the basis for the study of floc permeability. This study determined the porosity and structure of alum coagulation and activated sludge flocs. The porosity of these flocs can be expressed in geometric and mass terms. Yet mass porosity can be 10 times higher than geometric porosity due to an underestimation of floc density in the settling test. Given the more reliable data expressed by geometric porosity, an experimental method for studying the geometric porosity of aggregates was developed.; The average geometric porosity was 9% for alum flocs and 8% for activated sludge flocs. Similar average geometric porosity and size of the primary particles in these two aggregates suggested similar permeability of these flocs, while the settling behaviour of these flocs suggested that activated sludge flocs were more permeable than alum flocs. This suggested that the floc permeability couldn't be estimated based on the average porosity of the floc.; Interpretation of the geometric porosity data using the concepts of fractal geometry enabled three pore populations---small, medium and large---to be identified within alum and activated sludge flocs. Small pores had a cross-sectional area smaller than 3 mum2. The medium pores of alum flocs were smaller than 10 mum2, and the medium pores of activated sludge flocs were smaller than 20 mum2. Activated sludge flocs are more permeable than alum flocs because the pores forming flow channels---medium and large---are bigger in activated sludge flocs than the corresponding pores in alum flocs.; Based on the size of pores, permeability and structural models were proposed for the flocs studied. In the activated sludge floc model flocculi were two times larger than the flocculi in alum flocs. The size of the flocculi determines the size of pores facilitating the internal flow; therefore, it should be incorporated in the floc permeability models.; This study makes two recommendations: (1) developing floc permeability models that do not require floc porosity estimate; (2) re-calculation of floc mass transfer and drag force predictions using an improved estimate of floc permeability.
机译：絮凝孔隙度和结构的知识是研究絮凝渗透性的基础。这项研究确定了明矾凝结物和活性污泥絮凝物的孔隙率和结构。这些絮凝物的孔隙率可以用几何和质量表示。然而，由于沉降测试中絮凝密度的低估，质量孔隙率可能比几何孔隙率高10倍。考虑到用几何孔隙率表示的更可靠的数据，开发了一种研究骨料几何孔隙率的实验方法。明矾絮状物的平均几何孔隙率为9％，活性污泥絮状物的为8％。这两种聚集体中相似的平均几何孔隙度和初级颗粒尺寸表明，这些絮凝物具有相似的渗透性，而这些絮凝物的沉降行为表明，活性污泥絮凝物比明矾絮凝物具有更高的渗透性。这表明不能根据絮凝物的平均孔隙度来估算絮凝物的渗透率。使用分形几何学概念对几何孔隙率数据进行解释，可以在明矾和活性污泥絮凝物中识别出三个孔种群-小，中和大。小孔的横截面积小于3 mum2。明矾絮状物的中孔小于10 mum2，活性污泥絮状物的中孔小于20 mum2。活性污泥絮凝物比明矾絮凝物更具渗透性，因为在活性污泥絮凝物中形成流道的孔（中等和较大）比明矾絮凝物中的相应孔大。根据孔的大小，提出了絮体的渗透性和结构模型。在活性污泥絮凝模型中，絮凝物比明矾絮凝物中的絮凝物大两倍。絮状物的大小决定了促进内部流动的孔的大小。因此，应将其纳入絮凝渗透模型中。这项研究提出了两项​​建议：（1）建立不需要絮凝孔隙度估算的絮凝渗透率模型； （2）使用改进的絮凝渗透率估算值重新计算絮凝物传质和阻力预测。

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