Einfluss des hydraulischen Transportes auf die Konstitution, Erosion und Populationsdynamik aerober granularer Belebtschlammflocken
Final Report Abstract
In the present work, for better comprehension of the complexity of the biogranulation phenomena in an operating aerobic Sequencing Batch Reactor the process is studied, for the first time, from the fluid mechanical point of view. PIV investigations with video lamp present characteristic flow pattern in SBR during aeration phase. On the bottom large vortex exists, in the upper bioreactor part smaller eddies appear. Numerical investigations on the same system carried out simultaneously by Diez et al. (2007) depict identical flow characteristics. Analysing all PIV data it can be observed that fluid velocity increases with increasing vertical coordinate. Moreover, comparison of flow pattern in SBR at different moments of time and space indicates non stationary character of the analysed flow. Further investigations reveal strong influence of granules concentration on liquid velocity as well as flow pattern. Thereby, liquid velocity before wasting has significantly lower values than during wasting. This tendency is especially observed in the lowest bioreactor subdomain where granules concentration is the highest. Computed tangential and normal strain amount γ=28s-1 up to y=1 , ε=26s-1 which corresponds to dimensionless value of y=1 , ε=1, respectively. The latter seems to be crucial factor influencing granulation. As shown by Höfer et al. (2004) significant elongation of the floes appears already a ε=0.12. In the present work elongation rate is approximately ten times higher which means that normal strain rate affects substantially granulation process preventing the growth of fluffy floes as well as influencing their breakdown in early state of growth. Moreover, strain rate studies reveal increasing values of strain rate with increasing vertical coordinates. Similar tendency is shown by PIV studies with illumination provided by a video lamp as well as by He-Ne Laser. Moreover, the latter investigations enable more detailed analysis. Thereby, measurements for different wall interval indicate that liquid velocity as well as normal and shear strain rates increase with increasing wall distance. In contrast to liquid phase, the velocity of solid phase becomes lower with increasing vertical coordinate. Here, the concentration of granules affects the granula velocity, i.e. with increasing concentration, the velocity of dispersed phase decreases. This effect (similar as for liquid phase) is mainly caused by fractional interaction as well as collisions. Complementary to the field measurements (PIV) also one - point LDA studies are carried out. Also here an increasing tendency of axial velocity with rising aeration flow rate, increasing vertical coordinate and distance from SBR wall is noted. Concerning the latter, liquid velocity increases up to Z/D=0.10. Significant influence of granules and bubbles causes decrease of axial liquid velocity close to the SBR centre. Furthermore, comparing two and three phase flow, LDA measurements reveal big influence of third phase (granules) on flow pattern. As shown in the present work dimensionless mean axial velocity is higher for two phase flow. Additionally, the performed PSD analysis of the LDA signal indicates the existence of laminar flow. Kolmogorov -5/3 PSD slope law is not obeyed for different vertical coordinates as well as various wall intervals for two and three phase flow. Comparisons of PSD for two and three phase flow indicate that granules reduce velocity but do not change turbulence energy. In order to achieve an estimation of the overall load acting on the granulated sludge dimensional analysis of the fluid dynamical forces within the three phase flow in SBR is carried out. The dimensionless representation of the forces indicates buoyancy force as dominant one. Equivalent time averaged collisional force as well as drag force play also crucial role in SBR, however their dimensionless value are by one order of magnitude lower Fc/Fg=1.47x10-1 and Fd/Fg=1.31x10-1 than buoyancy force. Lift forces like Magnus Fm/Fg=2.43x10-2 and Saffman Fs/Fg=7.17x10-2 act also up to a certain extent on GAS. FG FG However, van der Waals force reaching the dimensionless value of Fw/Fg=2.69x10-1 is in fact Fc irrelevant for granules formation. Moreover, collisional forces play powerful role for granulation process. Basing on kinetic theory of gases as well as experimental investigations a decreasing tendency of particle - particle as well as particle - wall collision rate with increasing vertical coordinates is observed. Furthermore, microscopic analysis for different aeration flow rates clearly shows that granulation takes place only under appropriate hydrodynamic conditions. In the present study granules appear only for 4 l/min aeration rate, corresponding to SGV - 1.05 cm/s whereupon a lot of ciliates colonies live on GAS surface. Comparing granules occurrence for different aeration flow rates hydrodynamic selection of microorganisms as well as biomechanical fatigue effects are detected. Moreover, numeroexperimental and neuronumerical hybrid methods present a great benefit in save of the calculation time required for the prediction of the fluid flow and the granulation phenomena in the bioreactor. In the case of numeroexperimental hybrid the calculations cost up to 40% less time than the numerical prediction of the standard model without experimental data. Additionally, the convergence of the numerical simulation is improved and the results are much more similar to experimental observations. The acceleration with the factor 1.0E+05 is possible by using of the neuronumerical hybrid, which enables an estimation of ten characteristic parameters of the fluid flow. In comparison to CFD simulations, the neuronumerical hybrid estimates the characteristic parameters with an average relative error of 1.9%. The study of the results and the sensitivity analysis for each process parameter show significant influence of the air mass flow rate and the diameter of the air bubbles on the fluid flow and the granulation in the bioreactor. In the next perspective, the neuronumerical hybrid will be developed for prediction of complete velocity fields in a bioreactor.
Publications
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Diez L., Zima E., Kitsubun P., Hartmann C., Delgado A. 2005. Numerical Simulation of granula motion in Sequencing Batch Reactor (SBR). 11 th Workshop on Two-phase Flow Predictions, Ed. M. Sommerfeld, ISBN 3-86010-767-4
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Diez L., Zima B.E., Kowalczyk W., Delgado A. 2007 Investigation of multiphase flow in Sequencing Batch Reactor (SBR) by means of hybrid methods, Chemical Engineering Science, 67, 1803-1813
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Kowalczyk W., Zima B.E. Delgado A. 2007 A biocompatible seeding particle approach for m- PIV measurements of a fluid flow provoked by microorganisms, Experiments in Fluids, 43, 147- 150
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Zima B.E., Diez L., Kowalczyk W., Delgado A. 2006 Sequencing Batch Reactor (SBR) as optimal method for production of Granular Activated Sludge (GAS) - fluid dynamic investigations, Conference Biofilm Sytems VI, 24.-27.09.2006, Amsterdam, Niederlande
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Zima B.E., Diez L., Kowalczyk W., Delgado A. 2007 Optical in-situ techniques for investigations of a multiphase flow in Sequencing Batch Reactor, Lasermethoden in der Strömungsmesstechnik GALA 2007, 4.-6.09.2007, Rostock, Germany
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Zima B.E., Diez L., Kowalczyk W., Delgado A. 2007 Sequencing Batch Reactor (SBR) as optimal method for production of Granular Activated Sludge (GAS) - fluid dynamic investigations. Water Science and Technology, 55, 151-158
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Zima B.E., Kowalczyk W., Delgado A. 2006 Visualization of multiphase flow in Sequencing Batch Reactor (SBR) by Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV), Lasermethoden in der Strömungsmesstechnik GALA 2006, 5.-7.09.2006, Braunschweig, Deutschland
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Zima B.E., Kowalczyk W., Delgado A. 2007 Experimental investigations of multiphase flow in SBR, International Conference of Multiphase Flow, 9.-13.07.2007, Leipzig, Germany
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Zima B.E., Kowalczyk W., Hartmann C, Delgado A. 2005 Biologische Abwasserreinigung mittels Granula in einem Sequencing Batch Reaktor (SBR) - eine fluidmechanische Betrachtungsweise, Bremer Colloquium Produktionsintegrierte WasseWAbwassertechnik 2005 Innovative Verfahren zur industriellen Wasseraufbereitung, IUV und GVC/DECHEMA FG "SuPER", C59-C69, Bremen, Germany
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Zima B.E., Kowalczyk W., Hartmann C., Delgado A. 2005. Influence of velocity distribution in the multiphase flow on the building of aerobic granules in Sequencing Batch Reactor (SBR), Gesellschaft für Angewandte Mathematik und Mechanik (GAMM 2005), Luxembourg -, Proceedings in Applied Mathematics and Mechanics (PAMM), WILEY-VCH Verlag Weinheim, 5, 603-604
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Zima-Kulisiewicz B.E., Diez L., Kowalczyk W., Hartmann C., Delgado A. 2008 Biofluid mechanical investigations in Sequencing Batch Reactor (SBR). Chemical Engineering Science, 63, 599-608
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Zima-Kulisiewicz B.E., Kowalczyk W., Delgado A. 2007 Experimental and theoretical approach for analysis of a flow induced by microorganisms existing on a surface of Granular Activated Sludge, IUTAM Symposium on Advances in Micro- and Nanofluidics, 6.-8.09.2007, Dresden, Germany
