CFD as a Tool to Optimize Aeration Tank Design and Operation
Publication: Journal of Environmental Engineering
Volume 144, Issue 2
Abstract
In a novel development on previous computational fluid dynamics studies, the work reported here used an Eulerian two-fluid model with the shear stress transport – turbulence closure model and bubble interaction models to simulate aeration tank performance at full scale and to identify process performance issues resulting from design parameters and operating conditions. The current operating scenario was found to produce a fully developed spiral flow. Reduction of the airflow rates to the average and minimum design values led to a deterioration of the mixing conditions and formation of extended unaerated fluid regions. The influence of bubble-induced mixing on the reactor performance was further assessed via simulations of the residence time distribution of the fluid. Internal flow recirculation ensured long contact times between the phases; however, hindered axial mixing and the presence of dead zones were also identified. Finally, two optimization schemes based on modified design and operating scenarios were evaluated. The adjustment of the airflow distribution between the control zones led to improved mixing and a 20% improvement to the mass transfer coefficient. Upgrading the diffuser grid was found to be an expensive and ineffective solution, leading to worsening of the mixing conditions and yielding the lowest mass transfer coefficient compared with the other optimization schemes studied.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The research work of Dr. Anna M. Karpinska Portela was funded by the College of Engineering and Physical Sciences, University of Birmingham, U.K.
References
ANSYS version 17.0 [Computer software]. ANSYS, Sheffield, U.K.
Bokil, S. D., and Bewtra, J. K. (1973). “Influence of mechanical blending on aerobic digestion of waste activated sludge.” Advances in water pollution research, S. H. Jenkins, ed., Pergamon, Oxford, U.K., 421–438.
Bridgeman, J., Jefferson, B., and Parsons, S. (2008). “Assessing floc strength using CFD to improve organics removal.” Chem. Eng. Res. Des., 86(8), 941–950.
Cockx, A., Do-Quang, Z., Audic, J. M., Liné, A., and Roustan, M. (2001). “Global and local mass transfer coefficients in waste water treatment process by computational fluid dynamics.” Chem. Eng. Process., 40(2), 187–194.
Danckwerts, P. V. (1953). “Continuous flow systems. Distribution of residence times.” Chem. Eng. Sci., 2(1), 1–13.
Fayolle, Y., Cockx, A., Gillot, S., Roustan, M., and Héduit, A. (2007). “Oxygen transfer prediction in aeration tanks using CFD.” Chem. Eng. Sci., 62(24), 7163–7171.
Fogler, H. S. (1999). Elements of chemical reaction engineering, Prentice-Hall International, London.
Glover, G. C., Generalis, S. C., and Thomas, N. H. (2000). “CFD and bubble column reactors: Simulation and experiment.” Chem. Pap., 54(6A), 361–369.
Glover, G. C., Printemps, C., Essemiani, K., and Meinhold, J. (2006). “Modelling of wastewater treatment plants—How far shall we go with sophisticated modelling tools?” Water Sci. Technol., 53(3), 79–89.
Gresch, M., Armbruster, M., Braun, D., and Gujer, W. (2011). “Effects of aeration patterns on the flow field in wastewater aeration tanks.” Water Res., 45(2), 810–818.
Hibiki, T., and Ishii, M. (2000). “One-group interfacial area transport of bubbly flows in vertical round tubes.” Int. J. Heat Mass Transfer, 43(15), 2711–2726.
Higbie, R. (1935). “The rate of absorption of a pure gas into a still liquid during short periods of exposure.” Trans. AIChE, 31(2), 365–389.
Jesson, M. A., Bridgeman, J., and Sterling, M. (2015). “Novel software developments for the automated post-processing of high volumes of velocity time-series.” Adv. Eng. Software, 89, 36–42.
Karpinska, A. M., and Bridgeman, J. (2016). “CFD-aided modelling of activated sludge systems—A critical review.” Water Res., 88(Suppl C), 861–879.
Karpinska, A. M., and Bridgeman, J. (2017). “Towards a robust CFD model for aeration tanks for sewage treatment—A lab-scale study.” Eng. Appl. Comput. Fluid Mech., 11(1), 371–395.
Karpinska Portela, A. M. (2013). “New design tools for activated sludge process.” Ph.D. thesis, Faculdade de Engenharia, Univ. do Porto, Porto, Portugal.
Larsen, P. (1977). “On the hydraulics of rectangular settling basins, experimental and theoretical studies.”, Dept. of Water Resources Engineering, Lund Institute of Technology, Univ. of Lund, Lund, Sweden.
Le Moullec, Y., Gentric, C., Potier, O., and Leclerc, J. P. (2010). “CFD simulation of the hydrodynamics and reactions in an activated sludge channel reactor of wastewater treatment.” Chem. Eng. Sci., 65(1), 492–498.
Levenspiel, O. (1999). Chemical reaction engineering, Wiley, New York.
Menter, F. R. (1994). “Two-equation eddy-viscosity turbulence models for engineering applications.” AIAA J., 32(8), 1598–1605.
Mori, N., Suzuki, T., and Kakuno, S. (2007). “Noise of acoustic Doppler velocimeter data in bubbly flows.” J. Eng. Mech., 122–125.
Mueller, J. A., Boyle, W. C., and Pöpel, H. J. (2002). Aeration: Principles and practice, CRC Press, Boca Raton, FL.
Pereira, J. P., et al. (2012). “Activated sludge models coupled to CFD simulations.” Chapter 6, Single and two-phase flows in chemical and biomedical engineering, R. Dias, R. Lima, A. A. Martins, and T. M. Mata, eds., Bentham Science Publishers, Emirate of Sharjah, United Arab Emirates, 153–173.
Quasim, S. R. (1999). Wastewater treatment plants: Planning, design and operation, CRC Press, Boca Raton, FL.
Reardon, D. J. (1995). “Turning down the power.” Civ. Eng., 65(8), 54–56.
Roache, P. J. (1998). “Verification of codes and calculations.” AIAA J., 36(5), 696–702.
Samstag, R. W., et al. (2016). “CFD for wastewater treatment: An overview.” Water Sci. Technol., 74(3), 549–563.
Samstag, R. W., and Wicklein, E. (2012). “Application of CFD to activated sludge mixing analysis. CFD Workshop-presentation.” 3rd IWA/WEF Wastewater Treatment Modelling Seminar-WWTmod2012, International Water Association, London.
Talvy, S., Cockx, A., and Line, A. (2007). “Modeling of oxygen mass transfer in a gas-liquid airlift reactor.” AIChE J., 53(2), 316–326.
Tchobanoglous, G., Burton, F. L., Stensel, H. D., and Eddy, M. (2003). Wastewater engineering: Treatment and reuse, McGraw-Hill, New York.
VSA version 1.5.64 [Computer software]. Mike Jesson, Birmingham, U.K.
WEF (Water Environment Federation). (2009). Energy conservation in water and wastewater treatment facilities, McGraw-Hill, New York.
WPCF-ASCE (Water Pollution Control Federation and the American Society of Civil Engineers). (1988). “Aeration: A wastewater treatment process.”, ASCE, New York.
Yang, Y., et al. (2011). “Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model.” Water Res., 45(11), 3439–3452.
Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 144 • Issue 2 • February 2018
Copyright
©2017 American Society of Civil Engineers.
History
Received: Mar 28, 2017
Accepted: Jul 14, 2017
Published online: Nov 22, 2017
Published in print: Feb 1, 2018
Discussion open until: Apr 22, 2018
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.