Velocity Gradient Optimization in a Perforated Tray-Type Flocculator using OpenFOAM: CFD as a Tool in Water Treatment

Document Type : Regular Article

Authors

1 Department of Water Resources and Sanitation, Lavras Federal University, Postal Code 3037, Campus Universitario, Lavras, Brazil

2 Department of Mathematics and Applied Mathematics, Lavras Federal University, Postal Code 3037, Campus Universitario, Lavras, Brazil

10.47176/jafm.15.02.32372

Abstract

Analysis of the velocity gradient of flocculators through Computational Fluid Dynamics (CFD) simulation can be essential to the optimization of hydraulic conditions in Water Treatment Plants. This study aims to simulate the velocity field in the last tank of a perforated tray-type flocculator and quantify locally velocity gradient (G) through CFD. This stage of flocculation has a higher risk of flocs rupture when there are not adequate conditions. Thus, simulations occurred at the flocculator current operational flow rate (7 ls-1), and at full capacity (9 ls-1). An alternative cost-effective and easy to implement modification was tested by increasing the number of orifices in the flocculator trays. As result, the velocity field indicates the formation of dead zones at the edges of the tank for all simulations, which facilitates short circuit occurrences. This is an indicator of reductions in water treatment efficiency. After structural modifications, simulations indicate a reduction in dead zone areas. Plus, as the flow rate increases, the maximum G inside the structure increases considerably (184 to 266 s-1), causing a risk for floc rupture. However, changing the number of orifices from 22 to 33 creates conditions for the flocculator to operate at higher flow rates without increasing the velocity gradient.

Keywords


ABNT. (1992). NBR 12216: Project of water treatment plant for public supply, Brazilian Association of Technical Norms, Brasilia, Brazil.##
Alalm, M. G., M. Nasr and S. Ookawara (2016). Assessment of a novel spiral hydraulic flocculation/sedimentation system by CFD simulation, fuzzy inference system, and response surface methodology. Separation and Purification Technology 169, 137–150.##
Ansoni, J. L. and P. Seleghim (2016). Optimal industrial reactor design: Development of a multiobjective optimization method based on a posteriori performance parameters calculated from CFD flow solutions. Advances in Engineering Software, available.##
Bridgeman, J., B. Jefferson and S. A. Parsons (2009). Computational Fluid Dynamics Modelling of Flocculation in Water Treatment: A Review. Engineering Applications of Computational Fluid Mechanics.##
Bridgeman, J., B. Jefferson and S. A. Parsons (2010), The development and application of CFD models for water treatment flocculators. Advances in Engineering Software.##
Bridgeman, J., B. Jefferson and S. Parsons (2008). Assessing floc strength using CFD to improve organics removal. Chemical Engineering Research and Design.##
Camp, T. and P. Stein (1943). Velocity gradients and internal work in fluid motion. Boston Society of Civil Engineers.##
Castro, L. V., M. Rocha Vianna, C. de O. Ribeiro and L. S. Altair (2018). The influence of submerged orifice discharge coefficients in project of perforated tray-type hydraulic flocculator in water treatment plants. AIDIS Journal of Engineering and Environmental Sciences: Research, Development and Practice 11(1), 36–48.##
Holzmann, T. (2017). Mathematics, Numerics, Derivations and OpenFOAM. Configurable Distributed Systems, 1992. International Workshop On.##
Jarvis, P., B. Jefferson and S. Parsons (2004).The duplicity of floc strength. Water Science and Technology.##
Lira V. M. P. (2014) Numerical Modeling of a 90° Open channel Confluence Flow Using Openfoam CFD. M.Sc. dissertation, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.##
OpenFOAM (2021), The OpenFOAM Foundation Ltd, available at:  https://openfoam.org/version/7, Accessed 16.06.21.##
Richter, C. A. (2009). Água: Método e Tecnologia de Tratamento. São Paulo. Blucher.##
Salgado, A. L. (2006), Hydrodynamic Characterization of Chicaned Hydraulic Flocculators Through Three-Dimensional Numerical Simulation, M.Sc. Dissertation, Universidade Federal do Espírito Santo, Vitória, Brazil##
Samaras, K., A. Zouboulis, T. Karapantsios and M. Kostoglou (2010). A CFD-based simulation study of a large scale flocculation tank for potable water treatment. Chemical Engineering Journal 162, 208–216.##
Shah, M. S., J. B. Joshi, A. S. Kalsi, C. S. R. Prasad and D. S. Shukla (2012). Analysis of flow through an orifice meter: CFD simulation. Chemical Engineering Science 71, 400–309.##
Tambo, N. and H. Hozumi (1979). Physical aspect of flocculation process—II. Contact flocculation. Water Research 13(5), 441–448.##
Tambo, N. and H. Hozumi (1979). Physical characteristics of flocs—II. Strength of floc. Water Research.##
Vadasarukkai, Y. S., G. A. Gagnon, D. R. Campbell and S. C. Clark (2011). Assessment of hydraulic flocculation processes using CFD. Journal - American Water Works Association.##
Versteeg, H. K. and W. Malalasekera (2007). An introduction to computational fluid dynamics: the finite volume method. Actas Urologicas Espanolas.##
Vianna, M. R. (2019). Hydraulics Applied to Water Treatment Plant, 3i Editora Ltda, Belo Horizonte, Brazil.##
Vianna, M. R., L. V. Castro and C. Oliveira (2008). Perforated tray-type hydraulic flocculator for potable water treatment: concept and state of the art in Brazil. International Journal of Emerging Technology and Advanced Engineering 5 (3), 5–7.##
Wang, J., Y. Wu, H. Zhang and H. Jia (2014). Numerical and experimental investigation on integrated flocculation-membrane filtration process for the reactor configuration design and operational parameter optimization. Desalination.##
Zhang, J., A. E. Tejada-Martínez and Q. Zhang (2014), Developments in computational fluid dynamics-based modeling for disinfection technologies over the last two decades: A review. Environmental Modelling and Software##
 
Volume 15, Issue 2 - Serial Number 63
March and April 2022
Pages 387-397
  • Received: 14 November 2020
  • Revised: 16 August 2021
  • Accepted: 20 September 2021
  • First Publish Date: 30 January 2022