HYDRAULIC MODELING AND OPTIMIZATION OF WASTE STABILIZATION POND DESIGN FOR DEVELOPING NATIONS
By
DAVID OLATUNDE OLUKANNI, B.Eng, M.Eng, MNSE, COREN Reg. MATRIC NO: CUGP040109
Presented To
Department of Civil Engineering
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
1.1 Background to the study - .1
1.2 Problem statement - - - - .5
1.3 Aim of the research - ..6
1.4 Objectives - ..6
1.5 Scope of study - - - 6
1.6 Justification of study - ..7
1.7 Limitation of the work - - - - 7
Chapter 2: Literature review - ..8
2.1 The pressure on water demand ..8
2.2 Wastewater treatment systems in use - - - - ..9
2.3 Waste stabilization ponds - .11
2.3.1 Treatment units in Waste Stabilization. Ponds - - - .12
2.3.2 Anaerobic ponds - 13
2.3.2 .1 Design approach for anaerobic pond..15
2.3.3 Facultative ponds - - - - 17
2.3.3.1 Design criteria for facultative pond - - - ..17
2.3.3.2 Surface BOD loading in facultative ponds - - - 19
2.3.4 Model approaches for faecal coliform prediction in facultative pond - - 20
2.3.4.1 Continuous stirred reactor (CSTR) model approach..21
2.3.4.2 Dispersed flow (DF) model approach - - - .23
2.3.5 Maturation Pond..24
2.4 Waste Stabilization Ponds in Some Selected Institutions in Nigeria - ..26
2.4.1 Waste stabilization pond in University of Nssuka, Nigeria - ..29
2.4.2 Waste stabilization pond in Obafemi Awolowo University,
Ile-Ife, Nigeria - 30
2.4.3 Waste stabilization pond in Ahmadu Bello University, Zaria,
Nigeria - 32
2.5 Residence time-models in waste stabilization ponds - - - .35
2.5.1 Plug flow pattern - 35
2.5.2 Completely mixed flow pattern - - - - 37
2.5.3 Dispersed hydraulic flow regime - - - - 39
2.6 Wind effect and thermo-stratification on hydraulic flow regime - .42
2.7 Tracer experiment.43
2.8 Effects of baffles on the performance of waste stabilization - - .44
2.9 Computational Fluid Dynamics Approach to Waste Stabilization Ponds - - - 48
2.10 Laboratory scale ponds - - - - 56
2.11 Optimization of waste stabilization pond design - - - 59
2.