ABSTRACT
 
Wastewater stabilization ponds (WSPs) have been identified and are used extensively to
provide wastewater treatment throughout the world. It is often preferred to the conventional treatment systems due to its higher performance in terms of pathogen removal, its low maintenance and operational cost. A review of the literature revealed that there has been limited understanding on the fact that the hydraulics of waste stabilization ponds is critical to their optimization. The research in this area has been relatively limited and there is an inadequate understanding of the flow behavior that exists within these systems. This work therefore focuses on the hydraulic study of a laboratory-scale model WSP, operated under a controlled environment using computational fluid dynamics (CFD) modelling and an identified optimization tools for WSP.A field scale prototype pond was designed for wastewater treatment using a typical residential institution as a case study. This was reduced to a laboratory-scale model using dimensional analysis. The laboratory-scale model was constructed and experiments were run on them using the wastewater taken from the university wastewater treatment facility.
The study utilized Computational Fluid Dynamics (CFD) coupled with an optimization
program to efficiently optimize the selection of the best WSP configuration that satisfy
specific minimum cost objective without jeopardizing the treatment efficiency. This was
done to assess realistically the hydraulic performance and treatment efficiency of scaled
WSP under the effect of varying ponds configuration, number of baffles and length to
width ratio. Six different configurations including the optimized designs were tested in the
laboratory to determine the effect of baffles and pond configurations on the effluent
characteristics. The verification of the CFD model was based on faecal coliform
inactivation and other pollutant removal that was obtained from the experimental data.
 The results of faecal coliform concentration at the outlets showed that the conventional
70% pond-width baffles is not always the best pond configuration as previously reported
in the literature. Several other designs generated by the optimization tool shows that both
shorter and longer baffles ranging between 49% and 83% for both single and multi-
objective optimizations could improve the hydraulic efficiency of the ponds with different
variation in depths and pond sizes. The inclusion of odd and even longitudinal baffle
arrangement which has not been previously reported shows that this configuration could
improve the hydraulic performance of WSP. A sensitivity analysis was performed on the
model parameters to determine the influence of first order constant (k) and temperature
(T) on the design configurations. The results obtained from the optimization algorithm
considering all the parameters showed that changing the two parameters had effect on the
effluent faecal coliform and the entire pond configurations.  
This work has verified its use to the extent that it can be realistically applied for the
efficient assessment of alternative baffle, inlet and outlet configurations, thereby,
addressing a major knowledge gap in waste stabilization pond design. The significance of
CFD model results is that water and wastewater design engineers and regulators can use
CFD to reasonably assess the hydraulic performance in order to reduce significantly faecal
coliform concentrations and other wastewater pollutants to achieve the required level of
pathogen reduction for either restricted or unrestricted crop irrigation.

TABLE OF CONTENTS
         Title page – – – i
         Declaration – – – – ii           
         Certification – iii
         Dedication – iv
         Acknowledgements – – – – – v
         Table of Contents – – viii
         List of Plates – – – xv
         List of Figures – – xvi
         List of Tables – xxiv
         Abbreviations and symbols – – – xxvii
         Abstract – – – – xxxii

Chapter 1:   
Introduction – – 1
11     Background to the study – 1
12     Problem statement – – – – 5     
13     Aim of the research – 6
14     Objectives – 6
15     Scope of study – – – 6
16     Justification of study – 7
17     Limitation of the work – – – – 7
 
Chapter 2: Literature review – 8
     21    The pressure on water demand 8
     22    Wastewater treatment systems in use – – – – 9
     23    Waste stabilization ponds – 11
231    Treatment units in Waste Stabilization Ponds – – – 12   
        232    Anaerobic ponds – 13
             232 1 Design approach for anaerobic pond15      
       233    Facultative ponds – – – – 17
             2

331 Design criteria for facultative pond – – – 17  
             2332 Surface BOD loading in facultative ponds – – – 19
        234 Model approaches for faecal coliform prediction in facultative pond – – 20
             2341 Continuous stirred reactor (CSTR) model approach21
                2342 Dispersed flow (DF) model approach – – – 23
        235 Maturation Pond24
    24 Waste Stabilization Ponds in Some Selected Institutions in Nigeria – 26
            241   Waste stabilization pond in University of Nssuka, Nigeria – 29
            242   Waste stabilization pond in Obafemi Awolowo University,  
                           Ile-Ife, Nigeria – 30
               243   Waste stabilization pond in Ahmadu Bello University, Zaria,  
                           Nigeria – 32
   25    Residence time-models in waste stabilization ponds – – – 35
                 251 Plug flow pattern – 35
                 252 Completely mixed flow pattern – – – – 37
                 253 Dispersed hydraulic flow regime – – – – 39
   26 Wind effect and thermo-stratification on hydraulic flow regime – 42
  27 Tracer experiment43
  28 Effects of baffles on the performance of waste stabilization – – 44
  29 Computational Fluid Dynamics Approach to Waste Stabilization Ponds – – – 48
  210 Laboratory scale ponds – – – – 56
  211 Optimization of waste stabilization pond design – – – 59  
  212 Summary of literature review – – – – 61
   
Chapter 3:
Methodology – – – 62
  31   Description of the study area – – – – 62
32   Collection of data on Water demand – – – – 65
  33   Estimation of wastewater generated – – – – 66
  34   Study of existing wastewater treatment system – – – 66
  35   Analysis of wastewater samples70
  36   Design of the laboratory-scale plant layout – – – – 70
                  361 Design Guidelines for the University, Ota – – – 73
                         3611 Temperature (T) – – – – 73
                         3612 Population (P) – – – – 73
                         3613 Wastewater generation (Q) and Design for 20 years period – 73
                         3614 BOD Contribution per capita per day (BOD) – – 73
                         3615 Total Organic Load (B) – – – 74
                         3616 Total Influent BOD Concentration (Li) – – – 74
                         3617 Volumetric organic loading (λv) – – – 74
                         3618 Influent Bacteria Concentration (Bi) – – 74
                         3619 Required effluent standards – – – 74
37    Waste stabilization pond design – 75
             371 Design of Anaerobic Pond – – – – 75
             372 Design of Facultative pond76
             373 Design of Maturation Pond77
38  Design of Laboratory scale model – – – – 79
             381 Modeling of the Anaerobic Laboratory-scale pond – – 79
                382 Modeling of the Facultative Laboratory-scale pond – – – 81
             383 Modeling of the Maturation Laboratory-scale pond – – – 82
 39 Laboratory Studies – – 85
            391 Construction of the laboratory-scale waste stabilization ponds – 85
            392 Materials used for the construction of the inlet and outlet structures – 86
            393 Design of inlet and outlet structures of the WSP – – – 91
            394 Operation of the Laboratory-Scale waste stabilization pond – – 94
            395 Sampling and data collection – – – 95
                 3951 Water temperature – – – 95
                 3952 Influent and effluent samples – – – 95
310    Laboratory methods – 95
           3101     Feacal coliform – 96
           3102     Chloride – 96
           3103     Sulphate – 96
           3104     Nitrate – – 96
           3105     Phosphate – 96
           3106     Total Dissolved Solids – – – – 96
           3107     Conductivity – 97
           3108     pH – 97
311    Tracer Experiment – – 97
              3111   Determination of First Order Kinetics (K value) for Residence time  
                        distribution (RTD) characterization – – – 99
              3112    The gamma extension to the N-tanks in series model approach – 101
312   Methodology and application of Computational Fluid Dynamics model – 103
           3121 Introduction 103
           3122 CFD Model Application – – – – 106
                      31221 Simulation of fluid mechanics fecal coliform inactivation 106
                      31222 Constants used in the application modes – – 109
                      31223 Mesh generation for the computational fluid dynamics model110
                          31224 Model test for the simulation of residence time distribution
                                     curve in the CFD – – – 113
                     31225 Model test for the simulation of faecal coliform inactivation in
                                     the unbaffled reactor – – – – 114
                     31226  Model test for the simulation of faecal coliform inactivation in
                                    the baffled reactors – – – 116
             3123 Application of segregated flow model to compare RTD prediction  
                      and the CFD predictions for feacal coliform reduction – 122  
           3124 Summary of the CFD model methodology – – – – 124
  3131 Optimization methodology and application – – – 125    
             31311 Integration of COMSOL Multiphysics (CFD) with  
                           ModeFRONTIER optimization tool – – – 125
31312 The workflow pattern – – – – 126
             31313 Building the process flow – – – 127
             31314 Creating the application script – – 128
             31315 Creating the data flow – – – – 129
             31316 Creating the template input – – – 130
             31317 Mining the output variables from the output files – 131
3132 Defining the goals – – – – 132
             31321 The Objective functions for the optimization loop – – 132
             31322 The constraints for the optimization loop – – – 133
             31323 Cost objective Optimization – – – – 133
             31324 The DOE and scheduler nodes set up136
             31325 Model parameterization of input variables – – – 137  
             31326 DOE Algorithm – 140
             31327 Simplex algorithm – 140
              31328 Multi-Objective Genetic Algorithm II (MOGA-II) – – – – 141
             31329 Faecal coliform log-removal for transverse and longitudinal  
                           baffle arrangements143
     3133 Sensitivity Analysis on the model parameters – – – 145      
     3134 Running of output results from modeFRONTIER with the CFD tool – – 146
     3135 Summary of the optimization methodology – – – – 146
 
Chapter 4: Modeling results and Analysis  
    41 Model results for the RTD curve and FC inactivation for unbaffled reactors – 147  
    42 Initial Evaluation of baffled WSP designs in the absence of Cost using CFD151
        421 Application of segregated flow model to compare the result of RTD  
                 prediction and the CFD predictions for feacal coliform reduction – 163  
   43 Results of the N-Tanks in series and CFD models – – – 166
       431 General discussion on the results of the N-Tanks in series and CFD
                Models – 173
   44 Results of some selected simulation of faecal coliform inactivation for 80%
            Pond-width baffle Laboratory- scale reactors – – – 176
45 Optimization model results – 181
       451 The single objective SIMPLEX optimization configuration results – 181
       452 The Multi-objective MOGA II optimization configuration results – 195  
       453 Scaling up of Optimized design configuration – – 216
                 4531 Scaling up of Anaerobic Longitudinal baffle arrangement – – 216
                 4532 Scaling up of Facultative Transverse baffle arrangement – 218
                 4533 Scaling up of Maturation Longitudinal baffle arrangement – 219
                 4534 Summary of results of scaling up of design configuration – 220
      454 Results of sensitivity analysis for Simplex design at upper and lower  
                boundary – 220
     455 Results of sensitivity analysis for MOGA II design at upper and lower  
                     boundary – 235
     456 Summary of the optimization model result – – – – 249
 
Chapter 5: Laboratory-Scale WSP post-modeling results and verification of the  
                   Optimized models – – – – 250
51 Introduction – 250
52 Microbial and physico-chemical parameters – – – 251  
     521 Feacal coliform inactivation in the reactors – – – 251
     522 Phosphate removal256
     523 Chloride removal – – – – 258
     524 Nitrate removal – – – – 259
     525 Sulphate removal – – – – 260
     526 pH variation265
     527 Total dissolved solids removal – – – 266
     528 Conductivity variation – – – – 266
     529 Summary of laboratory experimentation – – – 267
 
Chapter 6: Discussion of results – – – – 269
         61 Experimental results of Laboratory-scale waste stabilization ponds  
               in series – 269
62 Hydraulic efficiency of CFD model laboratory-scale waste stabilization
               ponds in series – 270
         63 Optimization of laboratory-scale ponds by Simplex and MOGA II  
              Algorithms – 274
         64 Summary of discussion – – – – 275
 
Chapter 7: Conclusions and recommendations for further work – 277
        71 Conclusions277
        72 Contributions to knowledge – – – 278
        73 Recommendation for further work – – – 279
 
References – 280
   
Appendix A – 298
  A1     COMSOL Multiphysics Model M-file for Transverse baffle  
          anaerobic reactor – – – – , – 298
  A2     COMSOL Multiphysics Model M-file for longitudinal baffle  
          anaerobic reactor – 302
  A3     COMSOL Multiphysics Model M-file for Transverse baffle  
           facultative reactor306
  A4     COMSOL Multiphysics Model M-file for longitudinal baffle  
             facultative reactor – – – – 310
  A5     COMSOL Multiphysics Model M-file for Transverse  
          Maturation reactor – – – – 314
  A6     COMSOL Multiphysics Model M-file for longitudinal
          Maturation reactor – – – – 318
 
Appendix B322
B1     Transverse baffle arrangement scripting – – – 322
B2     Longitudinal baffle arrangement scripting – – 324

List of Plates
Plate 31       Tanker dislodging wastewater into the treatment chamber – – 67
Plate 32       The water hyacinth reed beds showing baffle arrangement  
                      at opposing edges68
Plate 33       The inlet compartment showing gate valve – – 68
Plate 34       The Outfall waterway leading into the valley below the cliff – 69
Plate 35       Effluent discharging through the outfall into the thick  
                     vegetation valley – – – – 69
Plate 36       Front view of the laboratory-scale pond – 88
Plate 37        Areal view of the laboratory-scale pond close to source of sunlight – – 88
Plate 38        An elevated tank serving as reservoir – 89
Plate 39        Inlet-outlet alternation of laboratory-scale WSP – – 89
Plate 310      Laboratory-scaled anaerobic ponds – – – 90
Plate 311      Laboratory-scaled facultative ponds – – – 90
Plate 312      Laboratory-scaled maturation ponds – – – 91
Plate 313       Inlet and outlet structure of the laboratory-scale  
                       waste stabilization pond – – – 92
Plate 314     Two 25-mm PVC hoses linked with the T-connector – – 92
Plate 315     Control valves screwed to position for wastewater flow – 93
Plate 316     Outlet structures connected to two pieces of ½ inch hoses  
                     for effluent Discharge – – – – 93
Plate 317      Tracer experiment with Sodium Aluminum Sulphosilicate – – 97
Plate 318     Tracer chemical diluting with the wastewater before  
                     getting to the outlet – – – – 98
Plate 319      Improvement in wastewater quality along the units – – 98

List of Figures
Figure 21      Waste stabilization pond configurations                                                    12
Figure 22      Operation of the Anaerobic Pond                                                               14
Figure 23      Operation of the facultative pond                                                               23
Figure 31      Bar chart of staff and student population trend                                          63
Figure 32      Template for calculating the per-capita water use                                     65
Figure 33      A sketch of the laboratory-scale WSP and operating conditions               72
Figure 34      Configuration of the designed WSP for Covenant University                  79
Figure 35      Different baffle arrangements with 70% pond width  
                        anaerobic pond                                                                                         99
Figure 36       Different baffle arrangements with 70% pond width  
                       facultative pond                                                                                       100
Figure 37       Different baffle arrangements with 70% pond width
                        maturation pond                                                                                     100
Figure 38      Data conversion for reactor length to width ratio to N for
                       N-tanks in series model                                                                          102
Figure 39      Description of length to width ratio for the laboratory-scale  
                       model                                                                                                      102
Figure 310     Triangular meshes for the model anaerobic reactor                               111
Figure 311     Triangular meshes for the model facultative reactor                             111
Figure 312     Triangular meshes for the model maturation reactor                            112
Figure 313    Model Navigator showing the application modes                                  113
Figure 314    Correlation data of the predicted-CFD and observed effluent Faecal  
                       coliform counts in baffled pilot-scale ponds                                         115
Figure 315   General arrangements of conventional longitudinal baffles of  
                     different  lengths in the anaerobic pond                                                  117
Figure 316   General arrangements of conventional longitudinal baffles of  
                     different lengths in the facultative pond                                                  117
Figure 317   General arrangements of conventional longitudinal baffles of  
                     different lengths in the maturation pond                                                 118
Figure 318      Mesh structure in a 4 baffled 70% Transverse Anaerobic reactor            118     
Figure 319      Mesh structure in a 4 baffled 70% Longitudinal Anaerobic reactor         119
Figure 320      Mesh structure in a 4 baffled 70% Transverse Facultative                       119
Figure 321      Mesh structure in a 4 baffled 70% Longitudinal Facultative  
                         reactor                                                                                                       120
Figure 322      Mesh structure in a 4 baffled 70% Transverse Maturation  
                         reactor                                                                                                       120
Figure 323      Mesh structure in a 4 baffled 70% Longitudinal Maturation   
                         reactor                                                                                                       121
Figure 324      Workflow showing all links and nodes in the user application  
                         interface                                                                                                    127
Figure 325      Logic End properties dialogue interface                                                   128
Figure 326      Data variable carrying nodes and the input variable properties  
                         Dialogue interface                                                                                    129
Figure 327      Template for the calculator properties and JavaScript  
                         expression editor                                                                                      130
Figure 328      Output variable mining interface and input template editor                    131
Figure 329      DOS Batch properties and batch test editor for mined data                    132
Figure 330      Constraint properties dialogue in the workflow canvas                          135
Figure 331      Objective properties dialogue in the workflow canvas                           135
Figure 332     DOE properties dialog showing the initial population of designs           136
Figure 333     Scheduler properties dialog showing optimization wizards                    137
Figure 334     Designs table showing the outcomes of different reactor  
                       configurations                                                                                          144
Figure 335     History cost on designs table showing the optimized cost     &a