A CFD model can simulate the hydrodynamics of a design before implementation: - Reducing lead-up times and costs - Ultimately lead to optimization of reactor configuration

1. Chemical Engineering Practice VI
Computational Fluid Dynamics
Carlos Teixeira – Paulo Ramos - Seyedali Emami
DEQ – FEUP 2011/2012

2. What is CFD?
The physical aspects of any fluid flow are governed by the
following three fundamental principles [1]:
 Mass is conserved; Continuity equation
 F = m·a (Newton’s second law); Momentum equation
 Energy is conserved. Energy equation
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3. Evolution of CFD applications:
Figure 1 - Mapping of the Evolution of Patent Figure 2 - Mapping of the Evolution of
Applications filing [2] Scientifics Articles over time [2]
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4. CFD Applications:
CFD can be used in [3]:
• Aerospace & Defense
• Automotive
• Construction
• Health care
• Energy
• Chemical Processing
• Etc.
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5. Application of CFD in water waste treatment
Activated sludge process (ASP) plants includes the following stages
[3]:
 Inlet works
 Primary settlement
 Activated sludge treatment
 Secondary settlement
 Tertiary treatment
CFD can be used to;
• Find capital cost savings,
• Achieve performance improvements,
• Energy savings.
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6. Application of CFD in water waste treatment [3]
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7. Company: Cambados WWTP
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8. Company : Cambados WWTP
• Working since 1985, this station was the first depuration station at
Oporto city. Despite being a potential user of CDF technology,
actually it isn’t.
• This WWTP receives the wastewater produced in several parishes
of Maia. The station have a capacity of 7040 m3 per day for a total
of 10000 habitants but it only use 1882 m3.
• This station treats wastewater from households and then they are
drained to river with an acceptable level of pollution through an
emissary.
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9. Company: Treatments
The wastewater
treatment process is
characterized by two
phases
Treatment Treatment of
of Liquid solid phase
phase
Mechanical
Thickening dehydration
Preliminary Biologic
treatment treatment
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10. Company: Treatments
• The decanted sludge is accumulated and then are returned
to the activated sludge tank. The decanted activated sludge,
when in excess, are send to a thickener tank to reduce the
moisture content. [4]
• After thickening, the sludge is dried, whose concentration
reaches 20% solids, and are destined for composing to the
Parada WWTP. [4]
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11. Current State of Design
Wastewater treatment vessels are sized according to required
pollutant removal: [5]
- Requires knowledge/assumptions of the flow regime (i.e.
hydrodynamics)
- Vessel configuration design to achieve flow type relies on
empirical correlations and heuristic techniques
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12. Hydrodynamics: Importance for Wastewater Treatment
The hydraulic behavior in an activated sludge tank, is of
fundamental importance for the efficiency of the process[6].
Hydraulic phenomena with negative effect on performance[6]:
-Short circuiting streams
-Dead volumes
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13. CFD: Alternatives
Models developed by the International Water Association are
useful tools for the process control. However, they are
unsuitable to model the influence of the reactor geometry; [7]
- Length/width ratio
- Presence of baffles
- Effluent inlet device
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14. CFD: Alternatives
Full-scale tracer tests are very informative when investigating
hydraulic situations in activated sludge tanks however [6];
-It claims a lot of personal
-And mean residence times are in order of days
So it becomes impracticable
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15. Why Design Using CFD in a WWTP?
A CFD model can simulate the hydrodynamics of a design before
implementation [8]:
- Reducing lead-up times and costs
- Ultimately lead to optimization of reactor configuration
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16. Why Design Using CFD in a WWTP?
Empty tanks in ETAR de Cambados
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17. Conclusions
• CFD modeling of wastewater processes is developing
• CFD design can lessen reliance on potentially
expensive trial-and-error methods
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18. Acknowledgments
We would like to thank to Eng. Atilia Silva for welcome us
at ETAR de Cambados.
ETAR de Cambados
Address:
Rua de Cambados
Vila Nova da Telha
Maia
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19. Question?
Thank
you
for
your
attention.
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20. References
[1] Anderson, Jr., John D.; Computational Fluid Dynamics. ISBN: 0-
07-113210-4
[2] Islabão, G. et al (2010). Technological Trends in CFD Applications.
Journal of Technologyl, Managment and Innovation, 76-83.
[3] http://www.ansys.com/
[4] http://www.ambiente.maiadigital.pt
[5] L. Benedetti et al (2006). Benchmarking of WWTP design by
assessing costs,. Water Science & Technology, 95–102.
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21. References
[6] Kjellstrand R. et al (2005) Short Circuiting in a Denitryfying
Activated Sludge Tank. Water Science & Technology, Vol. 52, No. 10-
11, pp 79-87, IWA
[7] Moullec, Y. L. (2010). CFD simulation of the hydrodynamics and
reactions in an activated sludge channel. Chemical Engineering
Science, 492 - 498.
[8] Brannock, Matthew (2003). Computational fluid dynamics tools
for the design of mixed anoxic wastewater treatment vessels PhD
Thesis, School of Engineering, The University of Queensland.
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