Toxicological Studies on Organic Manures Derived from Municipal Solid Waste in Makindye, Rubaga and Kawempe Divisions of Kampala, Uganda

ABSTRACT The study was carried out to estimate the levels of contamination and marketability of organic compost manures, derived from Kampala municipal solid wastes (MSW), sold along roads in the various suburbs of Kampala. The organic composts were sampled from five locations: Kawempe (KWP); Bwaise (BWS); Kitebi (KTB); Wankulukuku (WKK) and Ggaba-Kansanga (GGK~. The overall quality of the compost manures was determined by investigating selected physicochemical, trace metals and fertilizing properties, via standard methods. The pH of the manure was found to be within the range of 5.27-8.30. The electrical conductivity (EC) of manure samples ranged from 3.07 to 7.13 ~is/c1m A strong negative correlation was found between pH and both EC and trace metals in such manures. The study was found out that, apart from Cu and Zn which were within the permissible limits, the concentration of Pb, Cd, and Cr in all five areas were higher than the permissible limits set by UNBS, 2017. The results ofANOVA (F: 5, 0.05) showed that the there was significant difference in the manure samples collected from the various locations (p < 0.05). The study results indicated that majority of these manures had medium fertilizing potential but did not meet certain control guidelines set by standard agencies and may pose specific risks to the environment. Composts of KTB, BWS, KWP, GKK and were of medium quality (Class D) and had medium fertilizing potential. They could be conveniently applied in small scale farms and gardens. However, WKK, which did not comply for heavy metals should not be allowed into the market. It may only be used for developing lawns/gardens (with single application) or for the rehabilitation of degraded land. Post-treatment of these compost manures was recommended to improve their quality before being utilized for agricultural purposes.

TABLE OF CONTENTS

DECL~TION

APPROVAL

DEDICATION

ACKNOWLEDGE~NT iv

TABLE OF CONTENTS

LIST OF FIGURES ix

LIST OF TABLE

LIST OF APPENDICES

LIST OF ACRONYMS

ABSTRACT

CHAPTER ONE 1

iNTRODUCTION 1

1.1 Background of the Study 1

1.1.1 Solid waste generation and compost use in Kampala 1

I .1 .2 Assessment of solid wastes 3

1.2 Problem statement 4

1.3 Objectives

1.3.1 General objective

1.3.2 Specific objective 5

1.4 Research questions

1.6 Scope of the study 6

1.6.1 Content scope 6

1.6.2 Geographical scope 6

1.7 Justification of the Study

1.8 Significance of the Study 7

CHAPTER TWO 8

LITERATURE REVIEW 8

2.1 Composting 8

2.2 Composting ofBiodegradable Waste 9

2.3 Compost Manure Quality Testing 11

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2.4 Compost Manure Standard .12

2.5 Processing Factors Governing Compost Quality 12

2.6.1 Type of Feedstock Utilised 13

2.6.2 Major Organic Sources and Transformations 18

2.6.3 Source Segregation 20

2.6.4 Seasonal Variations 20

2.6.5 Pre-processing and Post-Processing Methods 21

2.6.6 Biological Processing 22

2.6.7 The Maturation Stage 23

2.6.8 Storage 24

2.7 Compost Evaluating Quality 24

2.7.1 pH 24

2.7.2 Organic Mailer 25

2.7.3 Moisture Content 25

2.7.4 Ash Content 26

2.7.5 Electric Conductivity 26

2.7.6 Nutrient Content 27

2.8 Trace Metals 30

2.8.1 Occurrences of trace metals 30

2.8.2 Sources of trace metals 32

2.8.3 Toxicity of trace metals 33

2.8.4 Use of chelating agents 41

2.8.5 Complications 41

2.8.6 Toxicity of heavy metals in soil applied with compost manure 41

2.8.7 Effects of compost manure on plant growth and nutrient uptake 43

CHAPTER THREE 45

MATERIALS AND MET1-JOD 45

3.1 Research Design

3.1.1 Study area 45

3.1.2 Samples collection 46

3.2 Preparation of Reagents 47

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3.3 Preparation of Standard Solutions 49

3.4 Sample preparation for trace metals analysis 50

3.5 Methods for Physicochemical Characterization of Samples 51

3.5.1 Determination of phosphorus in organic manure 51

3.5.2 Determination of nitrates in organic manure 51

3.5.3 Determination ofpH (10%) 52

3.5.4 Determination of electrical conductivity (10%) 52

3.5.5 Determination of moisture content 52

3.5.6 Determination ofAsh content 53

3.5.7 Determination of total volatile organic content 53

3.6 Quality Control 54

3.7 Statistical Analysis 54

3.8 Fertility and Clean Indices of Compost Manure

CHAPTER FOUR 58

RESULTS AND DISCUSSION 58

4.1 Physicochemical Parameters 58

4.1.1 pH

4.1.2 Electrical conductivity 60

4,1.3 Moisture content 61

4.1.4 Ash content (°“~) 62

4.1.5 Total Organic Matter 62

4.1.6 Nitrate 63

4.1.7 Phosphorus (P205) 64

4.2 Trace Metals 64

4.2.1 Cadmium (Cd) 67

4.2.2 Copper (Cu) 67

4.2.3 Lead (Pb) 68

4.2.4 Zinc (Zn) 69

4.2.5 Chromium 69

4.3.1 Pearson’s correlation 70

4.3.2 Correlation of Trace Metals of individual sampling areas 71

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4.3.3 Analysis of Variance (ANOVA) ~

4.3.4 Post Hoc Test (Least Significant Difference, LSD) 74

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS 79

5. ~ Conclusions

5.2 Recommendations 80

REFERENCES 83

APPENDICES