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ABSTRACT

 

Specific models for the design of pit latrines of different shapes and sizes are non-existent. What are
available are general design guides irrespective of the shape and size of latrine which may not give the
actual design parameters needed. Moreover, the physico-chemical and biological characteristics of pit
latrine sludge samples investigated by some researchers were limited and could not give the actual
situation in the pit latrines. The objectives of this research were to derive models for the rational design of
pit latrines of various shapes and sizes using data collected from 500 household pit latrines already filled
up, carry out laboratory analyses of sludge samples collected from fifteen (15) pit latrines for their
physico-chemical and biological characteristics and use the data to derive and verify the model for the pit
filling rate. It was therefore necessary that these models be derived and verified using both field and
experimental data as well as investigate the physico-chemical and biological characteristics of faecal
sludge samples from the pit latrines. In this research, models were derived for the design of various pit
latrine shapes and sizes using data obtained through the administration of designed questionnaire on 500
households having pit latrines. These models were calibrated and verified for the rational design of pit
latrines of various shapes and sizes using field data so collected. The regression coefficients for
calibration were 0.75, 0.65 and 0.50 and for verification were 0.97, 0.98 and 0.99 for square, circular and
rectangular pits respectively. Faecal sludge samples collected from fifteen (15) different pit latrines in the
study area were subjected to laboratory investigations for their physico-chemical and biological
characteristics. From the study, BOD, COD, total solids, suspended solids, volatile solids, moisture
contents and plate count showed decreasing trend throughout as the pit depth increased. On the other
hand, the pH presented double trends, increasing in some pits and decreasing in others. Temperature
presented double scenarios, increasing initially and decreasing afterwards. When BOD, COD, volatile
solids and temperature were measured against time and various pit layers, the Figures showed decreasing
trend in all the cases. The phosphorous content increased as the pit depth increased in all the 15 pit latrine
sludge samples analyzed. The biodegradability of faeces in all the pit latrines sampled in terms of COD
alone was 80.33% and 78.26% in terms of combined COD, BOD, total solids, volatile solids and
suspended solids. This attested for the reliability of this research. A model for the pit filling rate was
derived and verified using data obtained from laboratory analysis. The implication of this research is
availing of design models for the construction of various pit latrine shapes and sizes, increased knowledge
of physico-chemical and biological characteristics of faecal sludges in ordinary pit latrines and model for
pit filling rate. In conclusion, models have been derived and verified for the design of pit latrines of
various shapes. Pit filling rate model was also derived and verified. Better devices for measuring the
biodegradability of pit latrine sludges for COD and volatile solids as reference parameters should be
explored. Studies should be conducted on fresh pits of 1m3 to determine accurately, the time of filling.

 

TABLE OF CONTENTS

 

ITLE PAGE
CERTIFICATION i
DEDICATION ii
ACKNOWLEDGEMENT iii
ABSTRACT iv
LIST OF TABLES v
LIST OF FIGURES ix
LIST OF DIAGRAMS xi
CHAPTER ONE 1
INTRODUCTION `1
1.1 Background. 1
1.2 Relevance of This Research 3
1.3 Specific Objectives of This Research 3
1.4 Scope of Research 4
1.5 Limitations of this Research 4
1.6 Results 5
CHAPTER TWO 6
LITERATURE REVIEW 6
2.1 Types of Pit Latrine 6
2.2 Essential Components of a Pit Latrine 6
2.3 Functions of the Pit (the substructure) 6
xii
2.4 Pit Latrine Content 7
2.4.1 Description of Pit latrine Contents 7
2.4.1.1 Fresh Faeces and Solid Wastes 7
2.4.1.2:Higher Organics in Pit latrines 8
2.4.2Characteristics and Composition of human faeces. 8
2.4.3 Microbial composition of faeces 10
2.4.4 Pathogens in Excreta 10
2.4.5 Effect of Diet on Faecal Composition 11
2.4.6 Influence of Age on Faecal Composition 12
2.4.7 Daily Excretion of Urine and Faeces 12
2.5 Decomposition Processes of Faecal sludge In Pit Latrines 13
2.5.1 Type of Decomposition Process in Pit Latrine 14
2.5.1.1 Aerobic Decomposition 14
2.5.1.2 Anaerobic Decomposition 15
2.6 Oxygen Demand and Biochemical/Chemical oxygen demand 17
2.7. Factors Affecting the Efficiency of Faecal Decomposition Processes in Pit Latrine 19
2.7.1 Temperature. 19
2.7.2 Physical-Chemical Constituents 19
2.7.3 Nutrients 20
2.7.4 Phosphorus Conte nt 20
2.7.5 pH 21
2.7.6 Solids Content 21
2.7.6.1 Total Solids (TS) Content 21
xiii
2.7.6.2 Suspended Solids (SS) Content 23
2.7.6.3 Volatile Solids (VS) Content 23
2.7.6.4 Total Suspended Solids (TSS) Content 24
2.7.7 Collection Method 24
2.7.8 Climate 25
2.7.9 Moisture Content 25
2.7.10 Characteristics of the Surrounding Soil. 26
2.7.11 Topography of the Site 29
2.7.12 Contribution of Evapo-Transpiration 29
2.7.13WaterTable (WT) 30
2.7.14 Distances from Impermeable Layer and Groundwater Table 30
2.7.15Size/shape/dimensionsof the pit. 31
2.7.16 Microflora Present in the Pit 31
2.7.17 Inhibitory Substances 32
2.7.17.1Oxygen 32
2.7.17.2EffluentPurificationand Set-Back Distances 32
2.8 Treatment Targets 32
2.8.1 Pathogens in Faecal Sludge 33
2.8.2 Oil and Grease 33
2.9 Factors Affecting Filling Rates of Pit Latrines. 34
2.9.1 Design Factors 34
2.9.2 Toilet Usage 35
xiv
2.9.3 Storage Duration 35
2.9.4 Inflow and Infiltration 36
2.10 Stabilization 37
2.11 Sampling Procedures and Programmes 37
2.12 Theory and Design Considerations of Pit Latrine System 38
2.12.1 General Design Considerations 38
2.12.1.1 Design Population 38
2.12.1.2 Type of Anal Cleansing Materials Used 39
2.12.1.3Sludge Accumulation Ratio. 39
2.12.1.4 Expected Lifespan of the Pit 39
2.12.1.5 The Pit Volume 40
2.13 Previous Works on Pit Latrine Design Model 40
2.13.1 Characteristics of Pit Sludge 40
2.13.2 Existing Design Models for VIP Latrine 41
2.13.3 Ordinary Pit Latrine 42
2.13.4 Biological Degradation Processes of Faeces in Pit Latrine 43
CHAPTER THREE 44
RESEARCH METHODOLOGY 44
3.1 Description of Study Area 45
3.2 Site Visits 47
3.2.1 Questionnaire Administration in Households 47
3.2.2 Physical Field Measurements 48
xv
3.3 Analysis of the Data Obtained Using Questionnaire 48
3.4 Calibration and Verification 48
3.5 Determination of the Frequency/Duration of Defecation 49
3.6 Experimental Work 49
3.6.1 Samples Collection: 49
3.6.2. The Sampler 50
3.7 Laboratory Analyses of Faecal Sludges Collected 51
3.7.1 Reasons for Determining Faecal Sludge Parameters 51
3.7.1.1 Biochemical Oxygen Demand (BOD) 52
3.7.1.2 Chemical Oxygen Demand (COD) 52
3.7.1.3 pH 52
3.7.1.4 Plate Count 52
3.7.1.5 Suspended Solids (SS) 53
3.7.1.6 Total Solids 53
3.7.1.7 Volatile Solids 53
3.7.1.8 Phosphorus Content 53
3.7.1.9 Moisture Content 54
3.7.1.10 Temperature 54
3.8 Samples Preparation for Laboratory Analysis and Parameters Determination 55
3.8.1 Determination of pH Values 55
3.8.2 Determination of Plate Count 55
3.8.3 Determination of BOD 56
xvi
3.8.4 Determination of COD 56
3.8.5 Determination of Total Suspended Solids Content 56
3.8.6 Determination of Misture Content, Total solids and volatile Solids 56
3.8.7 Determination of Phosphate Content 57
3.8.8 Determination of Temperature 57
3.8.9 Laboratory Analysis of the Soils Encountered 59
CHAPTER FOUR 60
RESULTS AND DISCUSSION 60
4.1 Overview of Dicussion 60
4.2 Questionnaire Administration 60
4.2.1 Regression Equations 60
4.3 Variation of Frequency with Latrine Shapes 60
4.4 Variation of Frequency with Latrine Type 60
4.5 Variation of Frequency with Type of Anal Cleansing Materials 61
4.6 Variation of Pit Volume with Population of Households 63
4.7 Variation of Time Full with Population 64
4.8 Variation of Time Full with Volume 66
4.9 Variation of Sludge Accumulation Ratio with Population of Household 67
4.10 Variation of Sludge Accumulation Ratio with Time Full 69
4.11 Variation of Sludge Accumulation Ratio with Pit Volume 70
4.12 Variation of Time Full with Population/Unit Volume 71
4.13 Variation of Sludge Accumulation Ratio with population/Unit Volume 73
xvii
4.14 Comparison between Actual and Derived Pit Volumes 73
4.15 Correlation between Actual and Derived Pit Volumes 75
4.16 Calibration of Pit Design Models (Derived and other Models) 75
4.17 Variation of pH with Depth 77
4.18 Variation of BOD with Depth 81
4.19 Variation of BOD with Time 85
4.20 Variation of COD with Depth 87
4.21 Variation of COD with Time 92
4.22 Variation of Total Solids with Depth 93
4.23 Variation of Volatile Solids with Depth 97
4.24 Variation of Volatile Solids with Time 101
4.25 Variation of Moisture content with Depth 102
4.26 Variation of Plate count with Depth 107
4.27 Variation of Suspended Solids with Depth 110
4.28 Variation of Phosphorus Content with Depth 114
4.29 Variation of Temperature with Depth 118
4.30 Variation of Temperature with Time 122
4.31 Comparison of Mean values of Parameters Measured 124
4.31.1 Comparison of pH Data 124
4.31.2 Comparison of BOD Data 124
4.31.3 Comparison of COD Data 125
4.31.4 Comparison of Total Solids Data 126
xviii
4.31.5 Comparison of Volatile Solids Data 126
4.31.6 Comparison of Moisture Content Data 127
4.31.7 Comparison of Plate Count Data 128
4.31.8 Comparison of Phosphorus Content Data 128
4.31.9 Comparison of Suspended Solids data 129
4.31.10 Comparison of Temperature 130
4.32 Biodegradability of Faecal Sludge in Ordinary Pit latrine 130
4.33 Models Derivation 136
4.33.1 Regression Equations 136
4.33.2 Derivation of Pit Latrine Design Models 137
4.33.2.1 Square Pit Model Derivation 138
4.33.2.2 Circular Pit Model Derivation 138
4.33.2. 3 Rectangular Pit Model Derivation 139
4.34 Concept of Materials Balance in Pit Latrine 140
4.34.1 Derivation of Pit Filling Model 141
4.35 Models Verification 149
4.35.1 Verification of latrine Models 149
4.35.1.1 Verification of Square Pit latrine model 149
4.35.1.2 Verification of Circular Pit latrine Model 150
4.35.1.3 Verification of Rectangular Pit latrine Model 152
4.35.1.4 Determination of the Optimal section 153
4.35.2 Verification of Pit Filling Model 155
xix
4.35.3 Subsidence of Faecal Sludge in Pit Latrine 156
4.36 Reasons for the Variability of Data obtained in the Faecal Sludge samples Analyzed 157
CHAPTER FIVE 151
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 151
5.1 Summary 159
5.2 Conclusions 160
5.3 Recommendations 162
REFERENCES 165
APPENDICES: 187

Project Topics

 

CHAPTER ONE

INTRODUCTION
1.1 BACKGROUND.
Lack of access to basic sanitation and safe water supply facilities are major causes of diseases
and infant mortality in developing countries. Approximately 2.6 billion people worldwide lack
improved access to basic sanitation with the largest part residing in Africa and Asia. Safe
disposal of excreta has constituted one of the environmental problems facing mankind. Unsafe
disposal of excreta is one of the major sources of parasitic diseases causing untold hardship to
the populace both economically, socially and healthwise. Consequently around the world, there
is a drive to ensure the provision of safe and adequate sanitation and water supply facilities. In
line with this, MDG Objective Number 7 Target is to reduce the number of people without
access to basic sanitation by half by the year 2015. In developing countries, the number of people
with access to sanitation facilities has not substantially increased to match the growing
population. This has resulted in increased number of open defecation sites in both semi-urban
and rural communities.
The problem that has been bordering Engineers and others concerned in the provision of faecal
disposal facilities such as pit latrines has been that of deriving accurate models not only for the
fill-up rate and rate of degradation, but also the model for the rational design of pit latrines taking
into cognizance population, pit shape and dimensions, sludge accumulation rate, soil type and
conditions, etc. There have been limited attempts by researchers to derive these models but none
has been able to arrive at the desired result.
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Pit latrines when full often present some problems on the part of the users, maybe due to
economic reasons or lack of space to construct new ones. Theoretically, the rate of biological
conversion of large organic constituents to their simplest biological inert form or leaching
occurring within the pit should equal the filling rate. There is decreasing degradation rate as the
pit fills resulting in pits filling up faster than degradation occurs. Understanding of conditions
which affect the rates of biological degradation of pit latrine contents remains limited. Most of
the faecal disposal facilities in local community, Aku, for this research are pit latrines as shown
in the Figure 4.3.
As a contribution to providing improved basic and sustainable sanitation services especially to
households of semi-urban and rural areas, this research seeks to find solutions to the problems
attendant with latrine construction through the derivation of acceptable models using both field
and experimental data for the design. Such models will assist families to decide on a particular
latrine technology that will serve them for longer periods. This research will also go further to
derive accurate models for the fill-up rate and rate of degradation of pit latrine contents. This
research started with the administration of questionnaires to five hundred (500) households in the
study community to collect information on user population, user-behaviour, anal cleansing
materials, latrine types and dimensions, soil types and ground conditions, frequency of
defecation, soil-seal depths of filled latrines, age of pits, and reasons for pit latrine failure and
analysis of such information. The fifteen (15) household pit latrines sampled in this research
were scattered within the study area shown in Diagram 3.1. Subsequently, thorough laboratory
analyses of the physico-chemical and biological characteristics of the pit latrine faecal sludge
samples, collected with the aid of sampler at varying depths of the pit, were carried out using
standard methods of measurement in the laboratory (APHA, 1998).
3 | P a g e
1.2 RELEVANCE OF THIS RESEARCH
Worldwide and especially in the rural and semi-urban communities, pit latrines dominate the
other types of latrines in urban slums. Most people outside the metropolis in Nigeria now go for
pit latrines. From statistics, the most common form of low-cost sanitation is a pit latrine
(Wagner et al., 1958).
Many researches carried out earlier on pit latrines have not been able to come up with either the
acceptable models for the fill-up rate and rate of degradation of faeces in pit latrine or the real
models that will enable engineers design appropriately pit latrine volumes for both private and
public uses.
Based on the popularity of pit latrines attested by their increasing adoption in rural and semiurban
settlements, this research therefore is relevant as it seeks to derive more acceptable and
reliable models for the fill up rate and the rate of degradation of faeces in pit latrines as well as
models for the design of pit latrine volumes for different shapes of latrines for both rural and
semi-urban dwellers using data generated from the field and the laboratory.
1.3 SPECIFIC OBJECTIVES OF THIS RESEARCH
(1) To collect data from 500 households having existing several latrine types with respect to
their sizes and shapes, population of users, lifespan of already filled pits, soil-seal depth,
rate of degradation, soil type and ground conditions through physical examination, and
frequency of usage by household members. This questionnaire was administered in local
language to enable the interviewees understand the questions.
(2) To determine the physical, chemical and biological characteristics of pit latrine sludge
at different depths;
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(3) To derive expressions for the fill up rate and the rate of degradation of faeces in pit
latrine;
(4) To develop a model for designing pit latrines under different soil types and ground
conditions;
(5) To calibrate and verify the models derived using field/experimental data obtained in this
research.
1.4 SCOPE OF RESEARCH
This research was limited to the derivation of models that will aid the design of the capacity of
pit latrines of different shapes and dimensions for different population of users and under
different soil formations and ground conditions. It also sought to establish the rate of fill up of
faeces and the rate of degradation of faeces in pit latrines considering all the factors involved.
1.5 LIMITATION OF RESEARCH
The research was limited to the administration of questionnaires in five hundred (500)
households of Aku community; determination of the frequency of latrine usage and the period of
defecation by members of five (5) households for a period of 90 days in each household; and the
analysis of the data so generated. Data was collected from fifteen different filled-up pit latrines
and at different layers in each. The samples were analyzed to determine the degradability of the
faeces in pit latrines. The climax of this research was the derivation of a models for the design of
pit latrines for private and public use and their validation for real design and models for the fillup
rate and rate of degradation of faeces in pit latrines.
5 | P a g e
1.6 RESULTS
(1) Models were derived for the design of different shapes and sizes of pit latrines under
three different soil types and conditions for both private and public uses;
(2) Presentation of a model for the prediction of fill-up rate and rate of degradation of faeces
in pit latrines.
(3) Provision of a well-calibrated and verified model for rational design of pit latrine;
6 |

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