Modelling the Biodegradability of Sewage in Ordinary Pit Latrines.
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
TITLE 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 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
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
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
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 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
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
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 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
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
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
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 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 151
5.1 Summary 159
5.2 Conclusions 160
5.3 Recommendations 162
REFERENCES 165
APPENDICES: 187
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.
REFERENCES
Adhya, A.K, and Saha, S.K. (1986). Filling Characteristics of latrine Pits. In Water and Sanitation at Mid-Decade. Proc. Of the 12th WEDC Conference, Calcutta, 6-9 January (1986). WEDC, Loughborough. Pages 120-125.
Almeida, M.C; Butler, D and Friedler, E. (1999). At- Source Domestic Wastewater Quality. J. Urban Water. Vol.1 pp 49-45.
ALPHA (1998) Standard Methods for the Examination of Water and Wastewater. 20th Edition. American Public Health Association
APHA (2005). Standard Methods for the Examination of Water and Wastewater. American Public Health Association water quality Bulletin. 2005; Issue 46.
AL-Sa’ed, R. M. Y., Hithnawi, T.M. (2006). Domestic septage characteristics and co- treatment impacts of Albireh wastewater treatment plant efficiency. Dirasat Engineering Sciences 33(2), p.187-197.
Anderson G, Sallis P, Uyaniks S, eds. (2003). Anaerobic Treatment Processes. Handbook of Water and Wastewater Microbiology: Elsevier, N MDH, ed.
Anderson G, Donnelly T, Mckeown K. (1982). Identification and control of inhibition in the anaerobic treatment of industrial wastewater. Process Biochem.;17: 28 – 32.
Be the first to comment