Experimental and modeling investigation of sewage solids sedimentation based on particle size distribution and fractal dimension

Abstract

Sewage solids are usually characterized by non-specific parameters such as suspended solids. The suspended solids has been shown to be an inadequate index for advanced water treatment processes. In this study, the sewages solids particle size distribution was used to provide more detailed information on sewage characteristic. It is hoped that, by introducing particle size distribution, the mechanism of sewage solids sedimentations can be better understood. The particle size distribution of the domestic sewage was measured by the Malvern® laser scattering technique to link to its settlement efficiency. Experimental results show that 77 % of particle volume was removed during the 90 min settling, of which 71.2 % of particle volume was removed in the initial 30 min. The submicron particles were found to be removed by co-settling with large particles. The fractal dimensions of sewage solids could also be derived from the laser scattering measurement. The fractal dimension could also provide useful information on the shape and density of sewage solids. A mathematical model considering the particle sizes, shapes and density changes was then constructed to simulate the settlement of raw sewage particles. Comparison of the modeling results based on discrete and flocculant settling theory shows that settlement can be better predicted by considering the fractal nature of particles. The particle size distribution and fractal dimension data measured by Malvern® laser scattering technique have been shown to be valuable data for in-depth understanding of the mechanisms of sewage solids sedimentation.

The fate and behavior of selected endocrine disrupting chemicals in full scale wastewater and sludge treatment unit processes

“…They are also among the most estrogenic components of domestic sewage effluent (Jobling et al, 1998;Ternes et al, 1999a;Birkett and Lester 2003;Wu and He, 2010). The natural and synthetic estrogens are excreted primarily as a variety of inactive glucuronide or sulphate conjugates by the human population (Ternes et al, 1999b;D'Ascenzo et al, 2003;Gong et al, 2009;Fouial-Djebbar et al, 2010).…”

Particle associated polycyclic aromatic hydrocarbons in the atmospheric environment of urban and suburban residential area

“…Consequently, SPM has been recognized as a potent air pollutant in urban areas of Japan and considered as a criteria pollutant to be routinely monitored in ambient air. SPM pollution has been linked to bear remarkable effect on global climate change, too (Jacobson, 2002;Bandyopadhyay and Chattopadhyay, 2007;Feng et al, 2009;Wu and He, 2010). Although there is still a fundamental lack of understanding of the underlying mechanisms of their toxicity, one of the widely accepted hypotheses is that particulate toxicity not only depends on their size but also on their composition (Harrison and Yin, 2000;He et al, 2011).…”

Mathematical simulation on the oil slick spreading and dispersion in nonuniform flow fields

“…The random walk particle tracking (RWPT) are applied to describe the oil droplet's movement within the water column. In this method, each particle represents a fraction of the total oil and the two-dimensional movements are simulated by taking into account the effects of the physicochemical processes on the fate of the particles (Brovchenko et al, 2002;Elliot, 2004;Wu and He, 2010). Also, some models which developed from these methods are used to simulate the oil spreading under ice.…”