Analysis of particle size and fractal dimensions of suspensions contained in raw sewage, treated sewage and activated sludge

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 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

Analysis of Changes of Particle Size Distribution and Biological Composition of Flocs in Wastewater During the Growth of Algae

“…After reaching the stationary phase, flocs were retained on the pine bark filling, which resulted in a notable decrease of diameter of particles remaining in the volume of the treated sewage. This indicates that the size and shape of flocs has a significant effect on their properties and determines the method of their removal (Zhenhua et al 2001;Kuśnierz and Wiercik 2016;Huang et al 2010).…”

“…Together with other microorganisms, organic matter, and mineral matter, they form flocs which are characterised by multimodal size distribution and varied strength (Fettweis et al 2014). Determination of the size distribution of those particles in wastewater allows the choice of a suitable method of their removal (Bawiec et al 2017;Kuśnierz and Wiercik 2016;Huang et al 2010). That parameter, apart from density and porosity, is one of the factors in the estimation of the ability of flocs for sedimentation or flotation (Bawiec et al 2017;Wu and He 2012;Barbusiński and Kościelniak 1995).…”

“…However, they are complicated and time-consuming methods, and also require specialist knowledge in the field of phycology (Kuśnierz and Łomotowski 2015). Particle size distribution in the analysed material can be characterised on the basis of laser light dispersion with the use of a laser granulometer (Kuśnierz and Wiercik 2016). However, due to the geometric diversity of flocs, the use of a laser granulometer for the measurement of their size does not provide results as accurate as those obtained by means of a microscope (Jennings and Parslow 1988).…”

A New Method for the Process Division and Effect Evaluation of Coagulation Based on Particle Size Fractal Dimension

“…To achieve fine regulation of the coagulation process, scholars have attempted to divide the coagulation process. Sweeping current detector (SCD) analysis [11], small-angle laser light scattering [12], and average floc size measurements have been used to identify the stage in which flocs start to grow, but the relevant parameters in these methods could not accurately reflect the changes in the flocs at later stages in the coagulation process. He et al [13] found that the fractal dimension of flocs provided a new way of studying the coagulation process, as the process of floc growth could be described with a fractal dimension model and divided into two distinct phases.…”

“…To optimize coagulants and coagulation conditions, Margaritis et al [19] and Amjad et al [20] compared the fractal dimension of flocs and the distribution of fractal dimension, and on this basis, they studied the coagulation mechanism in water treatment. Kuśnierz and Wiercik [11] further used particle size and fractal dimensions to measure the effects of coagulation in wastewater treatment.…”