Design And Use of A Model Constructed Horizontal Subsurface Flow Wetland For Treating Tannery Wastewater By Means of Aquatic Plants

– Design And Use of A Model Constructed Horizontal Subsurface Flow Wetland For Treating Tannery Wastewater By Means of Aquatic Plants –

Abstract

In this study, a Laboratory-scale Horizontal Subsurface Flow Constructed Wetland has been designed, and three replicas constructed, cultivated with selected locally available aquatic plants Phragmites australis, Polygonum salicifolium + Ipomoea carnea, respectively, with the third cell un-vegetated, and used to treat tannery effluent.

The capacity or treatment efficiency or performance of the laboratory-scale Constructed Wetland in reducing the levelof physicochemical parameters (Biological Oxygen Demand, Chemical Oxygen Demand, Nitrates, phosphates, suspended solids and chromium) under a 6day Hydraulic RetentionTime was evaluated.

Physicochemical parameters were analyzed using standard methods. The highest removal efficiency for BOD (97.9%), COD (94.2%), NO3(54.4%), PO4(44.1%) and Cr (98.4%) was observed in the wetland cell planted with Phragmites australis, while the highest removal efficiency for TSS (92.6%) was observed in cell panted with a mix ofPolygonum salicifolium + Ipomoea carnea.

The un- planted cell showed lesser removal efficiency across all the selected parameters. Generally, through the 60 days of operation, the vegetated or planted cells showed better removal efficiency over the un-vegetated cell indicating that the selected aquatic plants are potential candidates for large-scale tannery wastewater treatment in Horizontal Subsurface Flow Constructed wetlands.

However, evaluation of the system over a longer period is required before concluding whether these plants in the subsurface constructed wetland are efficient for the primary treatment of tannery wastewater.

TABLE OF CONTENTS

Cover Page i
Title Page ii
Declaration iii
Certification iv
Dedication v
Acknowledgments vi
Table of Contents vii
List of Figures x
List of Tables xi
List of Plates xii
List of Appendices xiii
Acronyms xiv
Abstract xv
CHAPTER ONE: INTRODUCTION
1.1 Background of Study 1
1.2 Statement of Research Problem 5
1.3 Justification of Study 6
1.4 Aim and Objectives 7
1.5 Scope of Study 8
CHAPTER TWO: LITERATURE REVIEW
2.1 Tanning and Characteristics of Tannery Wastewaters 9
2.2 The Sources of Chromium in Tannery Effluent 10
2.2.1 Toxicity and environmental impacts of chromium 11
2.3 Treatment Methods of Tannery Wastewater 14
2.3.1 Physicochemical methods 14
2.3.2 Biological treatment methods 14
2.3.3 Constructed wetland technology 16
2.3.4 Configuration, zones, and components of constructed wetlands 26
2.4 Waste Removal Mechanisms and Efficiency of a Horizontal Subsurface 27
Flow Constructed Wetland
2.4.1 Heavy metals removal by subsurface flow wetlands 28
2.4.2 Biological oxygen demand (BOD) and chemical oxygen demand (COD) 29

2.4.3 Nitrogen removal 31
2.4.4 Phosphate removal 32
2.4.5 Removal of suspended solids 33
2.4.6 Influence of non-biological (Physical and Chemical) factors in wetlands 34
2.5 Role of Plants in Constructed Wetlands 36
2.5.1 Selection of plants for wetlands 37
2.5.2 Characteristics of the wetland plant Phragmites australis 38
2.5.3 Other wetland plants considered 41
2.6 Types of Constructed Wetland Design and Design Parameters 43
2.6.1 Rule of thumb 44
2.6.2 First-order plug flow models 45
2.6.3 Hydraulic design consideration 45
2.6.4 Aspect ratio 47
2.6.5 Bed slope 47
2.6.6 Hydraulic retention time 47
2.6.7 Hydraulic loading rate (HLR) and organic loading rate (OLR) 48
2.6.8 Flow velocity and flow depth 49
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials 50
3.2 Methods 52
3.2.1 Tannery effluent collection site 52
3.2.2 Experimental set-up 53
3.2.3 Laboratory analysis 57
3.2.4 Design considerations and parameters determination 61
3.2.5 Management of wetland plants used 66
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 The Aquatic Plants and Model Constructed Wetlands 67
4.2 Wastewater Characteristics 68
4.3 Biological Oxygen Demand and Chemical Oxygen Demand Removal 69
4.4 Suspended Solids Removal 71
4.5 Nutrient Removal 74
4.6 Chromium Removal 77
CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions 80
5.2 Recommendations 82
REFERENCES 84
APPENDICES 103

INTRODUCTION

Background of Study

The quantity of freshwater resources on earth is diminishing rapidly as a result of the increasing World population and urbanization, especially in developing countries(Bruch et al.,2011).

Already, many developing countries are facing acute scarcities of water due to rapid and unplanned development. In many developing countries, industrial effluents, sewage, and municipal wastewaters are discharged directly into water bodies, and such indiscriminate discharges further intensify the shortage of water supply due to pollution of freshwater sources.

In developing countries, the situation has become more severe and critical because of the lack of adequate sanitation. According to (2009),1.5 million children die annually worldwide, from water-borne , especially diarrhea, as a result of lack of clean drinking water.

The scarcity of safe is more severe in Africa and South Asia, where more than 80%of children’s deaths each year occur due to diarrhea (WHO, 2008).

According to Mara (2004), wastewater is water supply after it has been used. Industrial activities produce large volumes of wastewater which is a major source of pollution to the surface and groundwater.

Industrial is one of the problems presently facing Nigeria. Effluents generated by the industries are the major sources of water pollution. Contaminated air, soil, and water by effluents from the industries are associated with a heavy disease burden.

Some heavy metals contained in these (either in free form or adsorbed in the suspended solids) have been found to be carcinogenic (Tamburlini et al.,2002); while other chemicals are equally present, are poisonous depending on the dose and exposure duration.

REFERENCES

Akobundu I.O. and Agyakwa C.W. (1998). A handbook of West African Weeds. InternationalInstitute of Tropical Agriculture, Ibadan, Nigeria 106p.
Alves, M. M., Gonzalez, C.G., Guedes De Carvalho, R., Castanheira, J.M., Sol Pereira, M.C.,Vasconcelos, L.A.T. (1993). Chromium Removal in Tannery Wastewaters:„Polishing‟, PinusSylvestris Bark.Water Research, 27(8), pp-1333-1338.
Anthony,D.C.(1997).ModernTanningChemistry,BritishSchoolofLeatherTechnology,Nene College of higher education, Boughton Green Road. Mountain Park Northampton, UKNN2 7AL.Chemical Society Review. pp. 111 – 126.APHA (1995). Standard methods. 19th Edition. American Public Health Association,Washington, DC; USA
Asaye, K. (2009).Evaluation of Selected Plant Species for the Treatment ofTannery Effluentin a Constructed Wetland System; (Unpublished Thesis), AAU, Addis Ababa. Available at:en.wikipidia.org/winki/ITRC
Badejo, M. A. (2012). Ecosystem Engineering as a concept: The Significance of functionalClassification of the true engineers. Environtropica, 8: 194 – 199.
Bajza, Z. and Vreck, I. V. (2001). Water Quality Analysis of Mixture Obtained FromTannery Waste Effluent.Ecotoxicology and Environmental Safety; pp 15 – 18.
Bavor, H. J. and Adcock P. W. (1994). Relating Phosphorous Distribution within Wetlands totheir long term Performance. Proceedings, 2nd Annual Conference, Soil and Water Managementfor Urban Development – Creative Storm-water Management, Sydney, Australia, September.

StudentsandScholarship Team.