In recent years, it has been recognized that the laser diffraction gives valuable information on particle size distribution for all types of dry inorganic or even organic materials. With use of the laser diffraction and the laser granulometer, this paper presents the changes occurring in the granulometric distribution of algal agglomerates and the changes in values of percentiles 10, 50 and 90%, determined basing on volume distribution. While assessing the granulometric composition, the existence of a proportional relationship between the diameter values corresponding to the percentile of 10, 50 and 90% was observed. What is more, the obtained results give insight into the possibility of application of the general Avrami equation to describe the granulometric composition of the algal suspension through the analogy of crystals formation from saturated solutions. The analysis shows that the model described by the modified Avrami equation adequately matched the regression to the experimental data on the granulometric composition of algal suspensions. The values of the correlation coefficients were close to 1, which proves that the regression model explained nearly all cases by the dependent variable V i = F(d i ).

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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 fl ocs in activated sludge, in the aspect of control of single processes, i.e. sedimentation, dehydration, coagulation or fl occulation. 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 D 3 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 fl ow reactors are more effi cient 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 outfl ow. 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 signifi cantly more complex in the spatial aspect.Brought to you by | MIT Libraries Authenticated Download Date | 5/11/18 5:22 PM