See discussions, stats, and author profiles for this publication at: https://www.researchgate.
net/publication/299380060
Hydrodynamic Modelling of an UASB Reactor
Conference Paper · November 2015
CITATION READS
1 232
4 authors, including:
Silvano Pereira Renato Carrhá Leitão
Universidade Federal do Ceará Empresa Brasileira de Pesquisa Agropecuária (Embrapa)
4 PUBLICATIONS 38 CITATIONS 62 PUBLICATIONS 474 CITATIONS
SEE PROFILE SEE PROFILE
Iran E Lima Neto
Universidade Federal do Ceará
50 PUBLICATIONS 293 CITATIONS
SEE PROFILE
Some of the authors of this publication are also working on these related projects:
Laboratory studies of bubble plumes in uniform and stratified environments View project
Medium chain carboxylic acids production by anaerobic fermentation View project
All content following this page was uploaded by Renato Carrhá Leitão on 23 March 2016.
The user has requested enhancement of the downloaded file.
Hydrodynamic Modelling of an UASB Reactor
S.P. Pereira1, R.C. Leitão2, I.E. Lima Neto3, and C.A.S. Paiva1
1
Companhia de Água e Esgoto do Ceará - CAGECE, Rua Tomás Lopes, 85, Fortaleza-CE, Brasil.
(E-mail: silvanopereira@terra.com.br; silvano.pereira@cagece.com.br)
2
Brazilian Agricultural Research Corporation, Tropical Agroindustry National Centre.
(E-mail: renato.leitao@embrapa.br)
3
Universidade Federal do Ceará - UFC
(E-mail: iran@ufc.br)
Abstract
A pilot scale UASB reactor was modelled in order to evaluate its hydrodynamic behavior. CFD simulations using
COMSOL Multiphysics were carried out with a constant influent flow rate of 0.66 L/s and a hydraulic retention time of
6 h. The proposed numerical solution can represent the fluid dynamic behavior of the reactor in terms of velocity fields.
In the sedimentation zone, the vertical velocity components remained approximately constant with low values (<1m/h).
However, in sludge blanket region, a change in the velocity components has been observed, with greater intensity near
the walls, where a preferential pathway and a recirculation zone occurred. Although the upflow velocity on the top of
the sludge blanket and on the sedimentation zone were according to the recommendation (0.8-1.0m/h), many regions
around the walls presented high velocities (>10m/h). Since this velocity is a critical design parameter, changes in
reactor geometry may help to improve this distribution, which can be readily tested with the computational tool in use.
Keywords
CFD; hydrodynamic; simulation; UASB; wastewater.
INTRODUCTION
The performance of a UASB reactor, in terms of chemical oxygen demand (COD) removal and
energy yield, is usually governed by two main interrelated factors: microbiological processes and
hydrodynamics (Ren et al., 2009). Sufficient mixing is important for distribution of microorganisms
and nutrition, inoculation of fresh feed, homogenizing of the material and for the removal of end
products of the metabolism (Thorin, 2012). Its hydrodynamics will drive the mass transfer rates,
resulting in changes in biological reactions and, consequently, affecting the distribution of biomass
in different reactor regions, depending on the type of flow imposed (Carvalho et al., 2008). In
addition, hydraulic short-circuiting and stagnant zones may impair the efficiency of the reactors due
to decreased net volume and the hydraulic retention time. This work presents the hydrodynamic
behavior of an UASB, obtained by mathematical modeling.
MATERIAL AND METHODS
We used Computational Fluid Dynamics (CFD) tools from COMSOL Multiphysics, a commonly
used software platform based on advanced numerical methods to model and simulate multiphysics
problems. For this, we used the k- turbulent flow model to solve the equations of continuity,
conservation of momentum and turbulence. The k- model is based on semi-empirical equations to
model the turbulent kinetic energy transport (k) and its dissipation rate (ε) (Launder and Spalding,
1972). Although a multiphase model was in use, involving liquid, solid and gaseous phases
simulation, in addition to the kinetics involved in anaerobic digestion, at this moment only the
results regarding the liquid phase hydrodynamics are presented and discussed. The UASB geometry
was specified following the Brazilian Standards recommendations (NBR 12209: 2011) and
Tchobanoglous (2014), for a flowrate of 0.66 L/s (300 equivalent inhabitants) and hydraulic
retention time of 6 h. This reactor is under construction and will be used for calibration and
validation of this model. A three-dimensional mesh was adopted with a total of 80,347 tetrahedral
elements (Figure 1).
Figure 1. UASB reactor geometry and mesh, scale in meter.
RESULTS
Figure 2 shows the intensity and direction velocity. The numerical solution represents well the fluid
dynamics behavior of the reactor in terms of velocity fields. In the sedimentation zone the vertical
velocity components were approximately constant with low velocity gradients (<1m/h). However,
in the sludge blanket region, we observed a change in the velocity components, with greater
intensity near the walls, where a preferential pathway and a recirculation zone occurred. Although
the upflow velocity on the top of the sludge blanket and on the sedimentation zone were in
agreement with the recommendation (0.8-1.0h), many regions around the walls presented relatively
high velocities (>10m/h) when we compare with Tchobanoglous (2014).
Figure 2. Velocity intensity (m/h) and vector direction (right).
ACKNOWLEDGEMENTS
CAGECE, CNPq (process 460460/2014-5), EMBRAPA and UFC.
REFERENCES
Carvalho, K.Q., Salgado, M.T., Passig, F.H. Pires, E.C. 2008. Avaliação hidrodinâmica de reator UASB submetido à
variação cíclica de vazão. Eng. Sanit. Ambient. 13(2), 226-235.
Launder, B.E., Spalding, D.B. 1974. The numerical computation of turbulent flows. Computer Methods in Applied
Mechanics and Engineering 2, 269-289.
Ren, T., Mu, Y., Ni, B., Yu, H. 2009. Hydrodynamics of upflow anaerobic sludge blanket reactors. Environmental and
Energy Engineering 55(2), 516-528.
Tchobanoglous, G., Stensel, H.D., Tsuchihashi, R., Burton, F.L. (2014). Wastewater Engineering: Treatment and
Resource Recovery, 5th ed., Metcalf & Eddy I AECOM, McGraw-Hill Book Company, New York.
Thorin, E., Nordlander, E., Lindmark, J., Dahlquist, E., Yan, J., Fdhila, R. B. 2012. Modeling of the biogas production
process - A Review. International Conference on Applied Energy – ICAE.
View publication stats
