Examination Committee Dr. ir. Thomas Maere (Ghent University, Belgium) Prof. dr. ir. Miguel Peña (Universidad del Valle, Colombia) Prof. dr. ir. Jan Pieters (Ghent University, Belgium) Prof. dr. ir. Diederik Rousseau (HOWEST / Ghent University, Belgium) Prof. dr. ir. Marcos Von Sperling (Universidade Federal de Minas Gerais, Brazil)
Promotor Prof. dr. ir. Ingmar Nopens Department of Mathematical Modelling, Statistics and Bioinformatics BIOMATH Research Group: Model-based analysis and optimisation of bioprocess Faculty of Bioscience Engineering Ghent University
Co-Promotor Prof. dr. ir. Peter Goethals Department Applied Ecology and Environmental Biology Faculty of Bioscience Engineering Ghent University
Dean Prof. dr. ir. Guido Van Huylenbroeck
Rector Prof. dr. Paul Van Cauwenberge
Andrés Alvarado Martínez
Advanced Dynamic Modelling of
Wastewater Treatment Ponds
Thesis submitted in fulfilment of the requirements for the degree of Doctor (PhD) in Applied Biological Sciences
Dutch translation of the title: Geavanceerde dynamische modellering van afvalwaterzuiveringsbekkens
Please refer to this work as follows: Alvarado, A., 2013. Advanced dynamic modelling of wastewater treatment ponds. PhD thesis, Ghent University, Belgium.
ISBN: 978-90-5989-587-4 The author and the promoter give the authorisation to consult and to copy parts of this work for personal use only. Every other use is subject to the copyright laws. Permission for reproduce any material contained in this work should be obtained from the author.
Acknowledgements
I am writing these lines with a mixture of gratefulness and nostalgic feelings. Lots of memories surface: here and there (Cuenca, Ghent, Leuven…), working, enjoying and always commuting. Both in Ecuador and Belgium I was very fortunate to have the support of many people. These lines are devoted to all of them.
I would like to express my first and uppermost gratitude to my promotor Ingmar Nopens. I was very privileged to be part of his team at BIOMATH. I am very grateful for his timely and proficient reviews, discussions, ideas and solutions and also for his distinctive mentor character which boosted my motivation during the research. Even during my stays in Ecuador, I truly received a good support, supervision and encouragement to keep moving on. I honestly want to say that I had the guidance of an exceptional promotor.
My truthful thankfulness goes also to my co-promotor Peter Goethals for his reviews and advices during the research. I would like to offer my sincere thanks to the Flemish Inter-University Cooperation VLIR-UOS, which was the funding agency of this research. I am very grateful to Prof. Guido Wyseure, the coordinator of VLIR-UOS Programme who found a place for me at the Bioscience Faculty of Ghent University. I am also grateful for the help of Prof. Willy Bouwens, the Flemish coordinator of the Water Quality project and of Valerie Henrist, Elien and Piet, the scholar’s coordinators.
For the other members of BIOMATH, I only have words of gratitude. I really regret that my research did not allow me to stay in Ghent for longer periods so I could share much more with this extraordinary group of colleagues. My deepest thanks go to Sreepriya, Mehul and Youri for their skilful contribution to this research. Thanks also for your valuable help and support to Nicolás, Katrijn, Wouter, Wim, Thomas, Elena, Severine, Tinne, Timpe, Stijn, Giacomo, Karel, Webbey, and Abhishek.
I had the privilege to guide some excellent thesis students both in Ecuador as in Belgium. Thanks to Esteban E., Pablo, Sebastian, Magdalena, Esteban S. and Natascha.
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Acknowledgements
This research would not have existed without the support of the company ETAPA. I want to express my gratitude to all the directives. I am especially grateful to Galo Durazno, the chief of the Ucubamba waste stabilization pond system. He contributed to this research not only with the logistic support during the field works, but also with his expertise and knowledge of the WSP system. I am also sincerely thankful to Yolanda Torres, Mauro Pinos, Diego, María José, Cecilia, Rocío, Lenin, Ricardo, Sandra, Sebastián and to all the ETAPA workers who helped us during the field works at Ucubamba WSP.
During my long stays at Cuenca, I always found a place and the best working atmosphere at PROMAS. I am very grateful to Felipe Cisneros, director of PROMAS and the local coordinator of the VLIR-Water Quality project. A special gratitude is also expressed to the colleagues and members of the VLIR Project, Jorge Garcia, Juan Cisneros, Sandra Van Noten and Guillermina Pauta. My special thanks are also extended to Cristian, Vicente, Esteban, Diego, Juan Miguel, Anita, Eduardo, Pedro, Blanca, Gabriela, Yalo, Paul, Agustin, Sasha, Lucita, Andres, Juanito and all the colleagues of PROMAS. I would like to express my very great appreciation to the University of Cuenca directives and especially to the VLIR-Project coordinators, Fabián, Miguel and Arturo.
Muchas gracias a todos los colegas y amigos de la Universidad de Cuenca, estudiantes doctorales en Bélgica por el apoyo sincero en lo profesional y humano durante estos años.
Gracias infinitas a mi maravillosa familia, a mis padres Lauro y Margarita por su gran voluntad y energía para visitarme en este hermoso País. Su sabiduría, apoyo y cariño sin duda me dieron una gran motivación para culminar esta ardua pero satisfactoria etapa de mi vida. Gracias por cada palabra de aliento y cada oración a mis hermanos, sobrinos y sobrinas, cuñadas, cuñado, a mis suegros, tíos y tías. Gracias por su bendición Mamá Lolita y gracias a mis abuelit@s que agitan las nubes en este preciso instante sobre el Groot Begijnhof en Leuven para recordarme su inmenso cariño.
Finalmente quiero dedicar estas líneas a la persona que ha estado desde el empujón inicial de este viaje hasta su feliz culminación, siempre con todo el
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corazón en cada momento importante, en todas las tristezas, angustias y sacrificios y también en cada momento de felicidad y cada merecido descanso.
Gracias Osita por darme la inspiración para terminar esta etapa de mi vida. Gracias por tus sabios consejos, desayunos en bolsita para el tren, fiambres en lonchera, meriendas calientitas... Gracias por todo lo que me enseñaste en este camino, gracias por cuidar mi salud, gracias por las vitaminas contra mi voluntad y por arreglar mi escritorio, gracias por cada detalle, cada abrazo inmerecido.
Gracias por tu infinita paciencia, por todo el tiempo que me diste sacrificando tus tareas, gracias por tus desvelos y madrugadas para acompañarme.
Gracias a Dios que tengo la mejor esposa del mundo, sin ella no habría conseguido esto. Te amo mi Osita Vero.
Andrés
Ghent, February 2013
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Acknowledgements
iv
Table of Contents
CHAPTER 1. INTRODUCTION ...... 1 1.1 Background ...... 1 1.2 Objectives ...... 3 1.3 Thesis Outline ...... 4
CHAPTER 2. LITERATURE REVIEW ...... 7 2.1 Introduction ...... 7 2.1.1 Wastewater Treatment ...... 7 2.1.2 Why waste stabilization ponds? ...... 7 2.1.3 The conventional pond system ...... 9 2.1.4 Overview of main existing ponds ...... 10 2.1.4.1 Anaerobic Ponds ...... 10 2.1.4.2 Aerated Ponds ...... 11 2.1.4.3 Facultative Ponds ...... 11 2.1.4.4 Maturation Ponds ...... 11 2.2 Microbiological processes in waste stabilization ponds ...... 12 2.2.1 Anaerobic processes ...... 12 2.2.2 Aerobic processes ...... 12 2.2.2.1 Algal diversity ...... 14 2.2.2.2 Influence of environmental conditions ...... 16 2.2.3 Algal bioprocesses in waste stabilization ponds ...... 17 2.2.3.1 Algal growth ...... 17 2.2.3.2 Growth yield and maintenance energy requirement ...... 23 2.2.3.3 Oxygen production, respiration and photorespiration ...... 23 2.2.3.4 The Aqueous Carbonate System ...... 25 2.3 Hydraulics of waste stabilization ponds ...... 26 2.3.1 Tracer studies in ponds ...... 26 2.3.1.1 Tracer experiments set-up ...... 27 2.3.2 The Residence Time Distribution curve ...... 28 2.3.2.1 The pulse method ...... 29 2.3.2.2 The step method ...... 30 2.3.3 The Systemic models ...... 31 2.3.3.1 The dispersion model ...... 32
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Table of contents
2.3.3.2 Tanks-in-series modelling (TIS) ...... 35 2.4 Computational Fluid Dynamics models ...... 37 2.4.1 Introduction ...... 37 2.4.2 CFD models on Waste Stabilization Ponds ...... 37 2.4.3 Mathematical formulation ...... 41 2.4.3.1 Continuity and Momentum equations...... 41 2.4.3.2 Inert species transport...... 43 2.4.3.3 Turbulence ...... 43
CHAPTER 3. CFD MODELLING OF AERATED PONDS ...... 45 Abstract ...... 45 3.1 Introduction ...... 46 3.2 Materials and Methods ...... 49 3.2.1 The Waste Stabilization Pond System ...... 49 3.2.2 The Aerated Pond ...... 52 3.2.3 Experimental campaigns ...... 55 3.2.3.1 Velocities measurements ...... 55 3.2.3.2 Tracer Study ...... 55 3.2.4 Aerated pond operation ...... 57 3.2.5 CFD model specificities ...... 58 3.2.5.1 Geometry and discretization ...... 58 3.2.5.2 CFD code and submodels used ...... 59 3.2.5.3 Boundary conditions ...... 60 3.2.6 Modelling of propeller thrust ...... 61 3.2.7 Scenario Analysis ...... 62 3.3 Results and Discussion ...... 62 3.3.1 Single phase vs. two-phase CFD model ...... 62 3.3.2 CFD model validation ...... 65 3.3.3 CFD model vs. tracer experiment ...... 66 3.3.4 Scenario Analysis ...... 68 3.3.5 Oxygenation and energy consumption ...... 73 3.4 Conclusions ...... 74
CHAPTER 4. SLUDGE ANALYSIS IN FACULTATIVE PONDS ...... 77 Abstract ...... 77 4.1 Introduction ...... 78 vi
Table of contents
4.2 Methods...... 80 4.2.1 Description of the Facultative Ponds Studied ...... 80 4.2.2 Tracer experiment ...... 81 4.2.3 Sludge measurement ...... 81 4.2.4 CFD Modelling ...... 84 4.3 Results and Discussion ...... 86 4.3.1 Sludge accumulation rates ...... 86 4.3.2 Tracer Experiment vs. CFD ...... 88 4.3.3 RTD Analysis ...... 92 4.3.4 Liquid Flow Pattern by CFD ...... 92 4.3.5 CFD Sludge Accumulation Analysis ...... 94 4.4 Conclusions ...... 97
CHAPTER 5. DEVELOPING COMPARTMENTAL MODELS FOR SIMPLIFIED DESCRIPTION OF WSP HYDRAULICS ...... 99 Abstract ...... 99 5.1 Introduction ...... 100 5.2 Methods ...... 102 5.2.1 The Maturation pond studied ...... 102 5.2.2 Tracer Study...... 103 5.2.3 CFD Modelling ...... 103 5.2.4 Tanks-in-series modelling (TIS) ...... 105 5.2.5 Modelling of TIS and CM integrated with biokinetic model ...... 105 5.3 Results and Discussion ...... 106 5.3.1 CFD model simulation ...... 106 5.3.2 Compartmental model development ...... 108 5.3.2.1 Determination of different zones ...... 109 5.3.2.2 Determination of volume of different zones ...... 110 5.3.2.3 Determination of number of compartments per zone ...... 111 5.3.2.4 Determination of convective and exchange fluxes ...... 112 5.3.3 Tracer experiment vs. CFD ...... 113 5.3.4 Tanks-in-Series Analysis ...... 114 5.3.5 Compartmental model vs. tanks-in-series ...... 116 5.3.6 Coupled biological and hydrodynamic model analysis ...... 118 5.4 Conclusions ...... 119
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Table of contents
CHAPTER 6. BIOKINETIC MODELLING OF A WSP USING A SOUND HYDRAULIC MODEL ...... 121 Abstract ...... 121 6.1 Introduction ...... 122 6.2 Materials and Methods ...... 125 6.2.1 The pond and the compartmental model ...... 125 6.2.2 The biokinetic models ...... 125 6.2.2.1 The ALEX model...... 125 6.2.2.2 The SAH model ...... 126 6.2.3 Model implementation ...... 127 6.2.4 Influent data ...... 127 6.2.4.1 Fractionation models ...... 129 6.3 Results and Discussion ...... 130 6.3.1 Reconstruction of influent and effluent concentrations ...... 131 6.3.2 Performance of the ALEX and SAH models ...... 133 6.3.3 Comparison of coupled CM against TIS models ...... 139 6.4 Conclusions ...... 142
CHAPTER 7. CONCLUSIONS AND PERSPECTIVES ...... 143 7.1 General conclusions ...... 143 7.1.1 CFD models applied to waste stabilization ponds ...... 143 7.1.2 CFD models as decision support tools ...... 145 7.1.3 Compartmental models for simplified description of WSP hydraulics ...... 146 7.1.4 Coupling biokinetic models into a sound hydraulic model (CM) .. 147 7.1.5 Overall conclusion ...... 148 7.2 Perspectives and future work ...... 148
BIBLIOGRAPHY ...... 151 SUMMARY ...... 161 SAMENVATTING ...... 165 APPENDIX ...... 169 CURRICULUM VITAE ...... 183
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List of Symbols and Abbreviations a Platt’s coefficient [-] A Cross sectional area [m2] AL Aerated lagoon ASM Activated sludge model ASM1 Activated sludge model number 1 ASM2 Activated sludge model number 2 ASM3 Activated sludge model number 3 ATP Adenosine triphosphate -3 Ac Area under the concentration curve [kg.day.m ] b Platt’s coefficient [-] B Pond width [m] BC Boundary condition BOD Biochemical oxygen demand [g.m-3] BSM1 Benchmark simulation model number 1 C Actual concentration of dissolved oxygen [g.m-3] CFD Computational fluid dynamics CM Compartmental model COD Chemical oxygen demand [g.m-3] CSTR Continuous stirred tank reactor CWM1 Constructed wetland model number 1 -3 Ci Tracer concentration readings [kg.m ] -3 Cmax Maximum tracer concentration [kg.m ] -1 Cmin Minimum detectable tracer concentration [g.l ]
Ct Thrust coefficient [-] -3 CS Dissolved oxygen saturation concentration [g.m ]
C Turbulence model constant = 0.09 [-]
C1 Turbulence model constant = 1.44 [-]
C2 Turbulence model constant = 1.92 [-] d Dispersion number [-] D Longitudinal or axial dispersion coefficient [m2.day-1] DO Dissolved oxygen
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Symbols and Abbreviations
DS Dynamic simulation 2 -1 Dk Diffusion coefficient [m .s ] 2 -1 Dm Mass diffusion coefficient [m . s ]
Dp Propeller diameter [m]
Dt Diffusion coefficient [-]
fXCOD_VSS Ratio of particulate COD over VSS [-]
fXA Fraction of XA in particulate COD [-]
fXALG Fraction of XALG in particulate COD [-]
fXAMB Fraction of XAMB in particulate COD [-]
fXASRB Fraction of XASRB in particulate COD [-]
fXFB Fraction of XFB in particulate COD [-]
fXH Fraction of XH in particulate COD [-]
fXS Fraction of XS in particulate COD [-]
fXSTO Fraction of XSTO in particulate COD [-]
fSA Fraction of SA in soluble COD [-]
fSCH Fraction of SCH in soluble COD [-]
fSF Fraction of SF in soluble COD [-]
fSS Fraction of SS in soluble COD [-]
fi Limiting factors FAL Facultative aerated lagoon FM Fractionation model FSS Fixed suspended solids [g.m-3] GUI Graphical user interface -3 -1 GA-NH Algal growth on ammonia [g.m .d ] -3 -1 GA-NO Algal growth on nitrate [g.m .d ] h Length, depth [m] HRAP High rate algal pond HRT Hydraulic retention time [day] I Light intensity [E.m-2.s-1] -2 -1 I0 Light intensity at the water surface [μE.m .s ] k Turbulence kinetic energy [m2.s-2], -1 k1 Rate constant for Hydration CO [d ] -1 k2 Rate constant for Dissociation HCO [d ] x
Symbols and Abbreviations
KI Light saturation constant [E.m-2.s-1] -3 KCO2 Half saturation coefficient of CO2 for algal growth [mol.m ]. -2 -1 KI Light inhibition constant [μE.m .s ] -1 KL Interfacial transfer coefficient [m.day ]
KNHALG Saturation/inhibition factor of SNH [-]
KNOALG Saturation/inhibition factor of SNO [-]
KpH Half velocity constant [-]
Kr Dimensionless factor for tracer quantity [-] -3 KS Saturation coefficient of substrate “S” [g.m ]
K1 Dissociation constants for carbonate [-]
K2 Dissociation constants for bicarbonate [-] L Longitudinal length along the reactor, pond length [m] M Mass of tracer injected [kg] n Number of tanks -1 nrev Rotation speed of the propeller [rev.s ] NADPH Nicotinamide adenine dinucleotide phosphate-oxidase -3 NO2-N Nitrite-nitrogen concentration [g.m ] -3 NO3-N Nitrate-nitrogen concentration [g.m ]
OptpH Optimum pH for the algal culture [-]. p Pressure [Pa] pKeq1 Logarithmic acid dissociation constant for CO2-HCO3 equilibrium [-] P Mass fraction of pure tracer within tracer solution [-], PFD Photon flux density PFR Plug-flow reactor Pe Peclet number [-]
PD Applied engine power [W] q Constant load of tracer [kg.day-1] Q Flow rate [m3.day-1] Qr Recirculation flow [m3.s-1] R Reaeration through the air-water surface [g.m-3.day-1]; Recirculation flow [m3.s-1] RAE Relative Absolute Error
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Symbols and Abbreviations
RANS Reynolds-averaged Navier–Stokes RTD Residence time distribution RWQM1 River water quality model number 1 S Substrate concentration [g.m-3] SS Steady state SOD Sediment oxygen demand SRB Sulphate reducing bacteria SSE Sum of Squared Errors -3 SA Fermentation products as acetate [gCOD.m ] -3 SALK Soluble alkalinity component in ASM3 model [kg.m ] -3 SCH Soluble methane concentration [gCOD.m ] -3 SCO2 Mol concentration of CO2 [mol.m ] -3 SF Fermentable, readily biodegradable soluble COD [gCOD.m ] -3 SIC Total soluble inorganic carbon [kg.m ] -1 Sij Rate of deformation [m.s ]
SMx, SMy, SMz Sum of the body forces in the x, y, z direction respectively [N] -3 SNH Ammonia concentration [gN.m ] -3 SNO Nitrate concentration [gN.m ] -3 SS Soluble, readily biodegradable COD [gCOD.m ] t Time [day] T Temperature of the pond [oC] TIS Tanks-in-series TIS-BM TIS with recirculation flow from the last to the first tank TIS-R TIS with back mixing flow between all two adjacent tanks TSS Total suspended solids o T0 Reference temperature = 20 [ C] u Velocity components in x direction [m.s-1] -1 uavg Average flow velocity [m.s ] U Mean longitudinal velocity along the reactor [m.day-1] US Unsteady state U Mean velocity vector [m.s-1] v Velocity components in y direction [m.s-1] w Velocity components in z direction [m.s-1] V Volume of the reactor [m3] xii
Symbols and Abbreviations
VSS Volatile suspended solids [g.m-3] -1 v0 Maximum velocity at the face of the propeller [m.s ] vT Volume of tracer solution [litres] X Biomass concentration [g.m-3] -3 XA Autotrophs bacteria biomass [gCOD.m ] -3 XALG Algae biomass [gCOD.m ] -3 XAMB Acetotrophic methanogenic bacteria biomass [gCOD.m ] -3 XASRB Acetotrophic sulphur reducing bacteria biomass [gCOD.m ] -3 XFB Fermenting bacteria biomass [gCOD.m ] -3 XH Heterotrophs bacteria biomass [gCOD.m ] -3 XMI Mineral matter concentration [gCOD.m ] -3 XS Slowly biodegradable particulate COD [gCOD.m ] -3 XSTO Storage particulate COD [gCOD.m ] -3 XO Organic biomass concentration [g.m ] -1 ALG Temperature attenuation factor [d ] Density of tracer solution [kg.litre-1] Turbulence dissipation rate [m2.s-3] Insulation term in Dochain model [-]
k Scalar in transport equation [-] Light attenuation factor[m-1] -1 -1 3 p Extinction coefficient for algal biomass [m .gCOD .m ] -1 Extinction coefficient for water and colour [m ] -1 -1 3 Extinction coefficient for mineral matter [m .g .m ] -1 -1 3 Extinction coefficient for organic matter [m .g .m ] μ Specific growth rate of biomass [d-1] -1 μALG Growth rate of algae [d ] -1 μmax Maximum growth rate of biomass [d ]
μ Turbulent viscosity (eddy) Kinematic viscosity of the water [m2.day-1] Dimensionless time [-] Density of fluid [kg.m-3]
Turbulent Prandtl (Prt) number for = 1.3[-]
Turbulent Prandtl (Prt) number for k = 1.0 [-]
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Symbols and Abbreviations
σ Variance of RTD curve [day2] σ Dimensionless variance [-]
xx, yx, zx Viscous stresses acting in the x direction on a surface normal to the x, y, z direction respectively [Pa]
xy, yy, zy Viscous stresses acting in the y direction on a surface normal to the x, y, z direction respectively [Pa]
xz, yz, zz Viscous stresses acting in the z direction on a surface normal to the x, y, z direction respectively [Pa] Δx Distance between compartments [m]
I ̅ Light intensity mean value in Dochain model [μE.m-2 .s-1] ̅ Mean residence time [day]