Abstract The analysis of particle size in suspensions carried out with use of the laser diffraction method enables us to obtain not only information about the size of particles, but also about their properties, shape and spatial structure, determined basing on fractal dimension. The fractal dimension permits the evaluation of the interior of aggregates, at the same time showing the degree of complexity of the matter. In literature, much attention is paid to the evaluation of the fractal dimension of flocs in activated sludge, in the aspect of control of single processes, i.e. sedimentation, dehydration, coagulation or flocculation. However, results of research concerning the size of particles and the structure of suspensions existing in raw and treated sewage are still lacking. The study presents optical fractal dimensions D3 and particle size distributions measured with use of laser granulometer in raw and treated sewage and activated sludge collected from six mechanical-biological wastewater treatment plants located in the Lower Silesian region. The obtained test results demonstrate that wastewater treatment plants that use both sequencing batch reactors and continuous flow reactors are more efficient at capturing suspension particles of a size up to 30 μm and are characterized by an increased removal of particles of a size ranging from 30 μm to 550 μm to the outflow. Additionally, in the case of samples of treated sewage and activated sludge collected at the same location, at short intervals, similar particle distributions were observed. As far as the analysis of fractal dimensions is concerned, particles contained in the raw sewage suspension were characterized by the lowest values of the fractal dimension (median equals 1.89), while the highest values occurred in particles of activated sludge (median equals 2.18). This proves that the spatial structure of suspension particles contained in raw sewage was similar to a linear structure, with a large amount of open spaces, while the structure of particles contained in the activated sludge suspension was significantly more complex in the spatial aspect.

中文翻译：

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原污水、处理污水和活性污泥中悬浮液的粒径和分形维数分析

摘要 使用激光衍射法对悬浮液中的粒径进行分析，使我们不仅能够获得关于颗粒尺寸的信息，而且能够获得基于分形维数确定的关于它们的性质、形状和空间结构的信息。分形维数允许评估聚集体的内部，同时显示物质的复杂程度。在文献中，对活性污泥中絮体分形维数的评价，在对沉降、脱水、混凝或絮凝等单一过程的控制方面非常重视。然而，关于原污水和处理后污水中存在的颗粒大小和悬浮液结构的研究结果仍然缺乏。该研究介绍了使用激光粒度仪在从位于下西里西亚地区的六个机械生物废水处理厂收集的未经处理的和处理过的污水和活性污泥中测量的光学分形维数 D3 和粒度分布。获得的测试结果表明，同时使用序批式反应器和连续流反应器的废水处理厂在捕获尺寸高达 30 μm 的悬浮颗粒方面更有效，并且其特征在于对尺寸范围为 30 μm 至550 微米到流出。此外，在同一地点收集的处理过的污水和活性污泥的样本中，在很短的时间间隔内，观察到类似的颗粒分布。就分形维数的分析而言，原污水悬浮液中所含颗粒的特征在于分形维数的最低值（中值等于 1.89），而最高值出现在活性污泥颗粒中（中值等于 2.18）。这证明原污水中悬浮颗粒的空间结构类似于线性结构，具有大量的开放空间，而活性污泥悬浮液中的悬浮颗粒结构在空间方面明显更为复杂。