Equation for fitting dispersed systems gravity and centrifuge settling data

Liquid phase accumulation kinetics during sedimentation and centrifugation serves as a source of information about the average settling properties of dispersed systems. A power order fitting function is proposed for describing the dependence of accumulated liquid phase volume on settling time. The function validity was tested for numerous experimental settling data under gravitational and centrifugal forces for different dispersed systems. The obtained results give good correlation between experimental data and fitting curves even when settling displays a lag period. The main advantage of the proposed model is the possibility to fit the liquid phase accumulation kinetics in a wide range of settling time and solids concentration. The power order fitting function allows simulating the liquid phase accumulation in the case of limited experimental data.Fundação para a Ciência e a Tecnologia (FCT)FEDE

Simulation of liquid phase accumulation at centrifugal dewatering of activated sludge

Centrifugation of activated sludge is a frequently used dewatering process but there is a need for a fitting function for moderate and high sludge concentrations. In particular, liquid phase accumulation kinetics during centrifugation may be used as a source of information about sedimentation properties and governing mechanism of the cake formation. This will allow the obtention of the optimal parameters for the dewatering control and process optimisation. For this purpose, activated sludge at different concentrations was investigated on a laboratory centrifuge with centrifugation factor 2667. The following sludges were used in the experiments: 1) activated sludge from thickener (with and without floculant treatment); 2) sludge after industrial centrifuge decanter Flottweg Z62-4 collected from dumping pound; sludge (2) after anaerobic treatment; sludge (2) with a dispersed solid additive. Based on the obtained data, the following assumption was made: settling of the solid phase and cake compaction depends on the hindered settling velocity and sediment compression. Due to the applied centrifuge force, a primary cake skeleton from particular aggregates and flocs is formed. During this stage, free water is displaced from the space between aggregates/flocs with a further transition to the compaction of the sediment with the water being displaced from the pores of the flocs by a filtration mechanism until an equilibrium condition is reached. The liquid volume V vs. time t at hindered settling and sediment dewatering can be represented in the form Vα tⁿ, where n ≤1.0. Therefore, in log-log coordinates, the kinetics of liquid accumulation have a linear dependence lg(V ) α n lg(t) in both settling and compaction stages. This assumption was confirmed for different types of activated sludge. Using asymptotical analysis in the function form F(t,V) , a dimensionless fitting function was obtained that describes the centrifugation of activated sludge. For highly concentrated sludge, it was found that the dewatering occurs as cake compression. Analysis of deformation models leads to the conclusion that for the compressible cake it is necessary to introduce a parameter characterising the cake plasticity dependence on the centrifugation time. Developed model was used for fitting numerous experimental data. The main advantage of proposed model is the possibility to fit the liquid phase accumulation kinetics during centrifugation in a wide range of the activated sludge concentration, from suspension up to structured and paste-like cake consistency. The extension of this model to other slurries requires further investigation

Porous media, applications in biotechnology

After describing the main characteristics of porous media (porosity, tortuosity, permeability, and diffusivity), the role of porous media in mass transfer is analyzed with the help of numerical examples. Significant differences between the behavior of inert and biological porous media with respect to the response to external factors are considered. Current and prospective applications of porous media in biotechnology and biomedicine are highlighted.info:eu-repo/semantics/publishedVersio

Simulation of liquid phase accumulation for the centrifugal dewatering of activated sludge

Centrifugation of activated sludge is a frequently used dewatering process but, in spite of this, there is a need for a fitting function for moderate and high sludge concentrations. Liquid phase accumulation kinetics during centrifugation may be used as a source of information about the sedimentahon properties and the governing mechanism during cake formation. For this purpose, activated sludge at different concentrations was investigated on a laboratory centrifuge with a centrifugation factor of 2667. The following sludges were used in the experiments: 1. Activated sludge from a thickener (with and without flocculant treatment) 2. Sludge taken after an industrial centrifuge decanter, treated with Flottweg Z62-4 flocculant and collected from a dumping pound 3. Sludge (2) after anaerobic treatment 4. Sludge (2) with a dispersed solid additive. Using the experimental data for an asymptotical analysis, a dimensionless fitting function was obtained that adequately describes the dependence of liquid volume vs. time for the centrifugation of activated sludge. For the highly concentrated sludge it was found that the dewatering occurs through cake compression. Analysis of deformation models leads to the conclusion that for the compressible cake it is necessary to introduce a parameter characterising the cake plasticity dependence on the centrifugation time. The developed model was validated by fitting numerous experimental data. The main advantage of the proposed model is the possibility to fit the liquid phase accumulation kinetics during centrifugation over a wide range of activated sludge concentration values, from suspensions up to structured and paste-like cake consistency.Fundação para a Ciência e a Tecnologia (FCT).FEDER