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Computational fluid dynamics in water waste treatment plants

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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

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Computational fluid dynamics in water waste treatment plants

  1. 1. Chemical Engineering Practice VI Computational Fluid Dynamics Carlos Teixeira – Paulo Ramos - Seyedali Emami DEQ – FEUP 2011/2012
  2. 2. What is CFD?The physical aspects of any fluid flow are governed by thefollowing three fundamental principles [1]: Mass is conserved; Continuity equation F = m·a (Newton’s second law); Momentum equation Energy is conserved. Energy equation 2
  3. 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] 3
  4. 4. CFD Applications:CFD can be used in [3]:• Aerospace & Defense• Automotive• Construction• Health care• Energy• Chemical Processing• Etc. 4
  5. 5. Application of CFD in water waste treatmentActivated sludge process (ASP) plants includes the following stages[3]: Inlet works Primary settlement Activated sludge treatment Secondary settlement Tertiary treatmentCFD can be used to;• Find capital cost savings,• Achieve performance improvements,• Energy savings. 5
  6. 6. Application of CFD in water waste treatment [3] 6
  7. 7. Company: Cambados WWTP 7
  8. 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. 8
  9. 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 9
  10. 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] 10
  11. 11. Current State of DesignWastewater treatment vessels are sized according to requiredpollutant removal: [5]- Requires knowledge/assumptions of the flow regime (i.e. hydrodynamics)- Vessel configuration design to achieve flow type relies onempirical correlations and heuristic techniques 11
  12. 12. Hydrodynamics: Importance for Wastewater TreatmentThe hydraulic behavior in an activated sludge tank, is offundamental importance for the efficiency of the process[6].Hydraulic phenomena with negative effect on performance[6]:-Short circuiting streams-Dead volumes 12
  13. 13. CFD: AlternativesModels developed by the International Water Association areuseful tools for the process control. However, they areunsuitable to model the influence of the reactor geometry; [7]- Length/width ratio- Presence of baffles- Effluent inlet device 13
  14. 14. CFD: AlternativesFull-scale tracer tests are very informative when investigatinghydraulic situations in activated sludge tanks however [6]; -It claims a lot of personal-And mean residence times are in order of daysSo it becomes impracticable 14
  15. 15. Why Design Using CFD in a WWTP?A CFD model can simulate the hydrodynamics of a design beforeimplementation [8]:- Reducing lead-up times and costs- Ultimately lead to optimization of reactor configuration 15
  16. 16. Why Design Using CFD in a WWTP? Empty tanks in ETAR de Cambados 16
  17. 17. Conclusions• CFD modeling of wastewater processes is developing• CFD design can lessen reliance on potentially expensive trial-and-error methods 16
  18. 18. AcknowledgmentsWe would like to thank to Eng. Atilia Silva for welcome usat ETAR de Cambados.ETAR de CambadosAddress:Rua de CambadosVila Nova da TelhaMaia 17
  19. 19. Question? Thank you for your attention. 17
  20. 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 byassessing costs,. Water Science & Technology, 95–102. 18
  21. 21. References[6] Kjellstrand R. et al (2005) Short Circuiting in a DenitryfyingActivated Sludge Tank. Water Science & Technology, Vol. 52, No. 10-11, pp 79-87, IWA[7] Moullec, Y. L. (2010). CFD simulation of the hydrodynamics andreactions in an activated sludge channel. Chemical EngineeringScience, 492 - 498.[8] Brannock, Matthew (2003). Computational fluid dynamics toolsfor the design of mixed anoxic wastewater treatment vessels PhDThesis, School of Engineering, The University of Queensland. 19

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